Agroclimatic analysis for reducing planting risks in Burkina Faso and Senegal

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Araya, P. K. Jha, I. A. Ciampitti, V. Sharda, P. V.V. Prasad This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7180722/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Dec, 2025 Read the published version in Theoretical and Applied Climatology → Version 1 posted 12 You are reading this latest preprint version Abstract This study was carried out in Burkina Faso and Senegal, West Africa. The purpose of the study was to (i) characterize the climate and assess the occurrence of meteorologically below average rainfall years, (ii) evaluate the rain onset, cessation, and length of growing period, and (iii) identify the optimal planting time for maize, sorghum, pearl millet and peanut. The study showed that there is a latitudinal difference in rainfall distribution and frequency from south to north in both Burkina Faso and Senegal. Over the past 40 years period (1981–2020), at least 6 years were identified as meteorologically drought years with a spatiotemporal variation in the severity. The most severe one occurred in 1983–84. Occurrence of below average rainfall substantially reduced after 1990 for both Burkina Faso and Senegal. The number of rainy days with rainfall values ≥ 5 or ≥ 10 mm for each growing seasons in both Burkina Faso and Senegal were highly correlated with the annual total rainfall. The lowest and highest rainfall values corresponded to northern and southern locations, respectively. Planting based on onset estimated by weekly cumulative rainfall probabilities in three out of four years meeting 50% weekly cumulative reference evapotranspiration enhanced yield and found to be suitable planting for sorghum, maize, millet and peanut in the south and central part of both countries. Yield followed the spatial rainfall and temperature gradient in both Burkina Faso and Senegal. The northern most locations were dry and thus it is not optimal to grow grain crops without irrigation. climate change onset planting date food security drought West Africa Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Climate variabilities remain a risk factor and challenge for agri-food systems. Agriculture is susceptible to climate variability and change. Agriculture in most of the semi-arid and arid countries, particularly in Africa, depends on rainfall (rainfed agriculture), which is influenced by climatic variability and seasonal weather changes (Maguèye and Ndao 2013 ). As such, with limited irrigation, technology adoption, and economic and institutional infrastructure, African agriculture is vulnerable to climate variability and changes (Sultan and Gaetani 2016; Sylla et al. 2018 ). Global surface temperatures increased between 0.95 and 1.2°C during the period 2010–2020 relative to the preindustrial era (1850–1900) (Arias et al. 2021 ) and are expected to increase under future scenarios (Sylla et al. 2016). Rainfall and seasonal temperature play a significant role in crop production, particularly in the length of the growing season (LGP) in West Africa (Roudier et al. 2011 ; Maguèye and Ndao 2013 ). Understanding the adverse effects of rainfall and temperature on the LGP, crop evapotranspiration, and optimal planting date would be critical and important for developing climate-resilient strategies and assisting farmers to understand the possible impacts and address the problem in a timely and cost-effective manner. Drought is one of the major challenges in West Africa, especially in the 1970s and 1980s (Dabiré et al. 2012 ; Dembélé and Zwart 2016 ; Sultan and Gaetani 2016). The north-central and northern Burkina Faso and Senegal are susceptible to climate variability and change (Defrance et al. 2020 ). Characterizing the rainfall that includes rainfall distribution, frequency, and the severity of meteorological drought could be useful to understand the impacts on crop production and develop crop suitability for a region. In this study, meteorological drought refers to a season during which the received sum of rainfall falls below normal when compared to the long-term average (Harpold et al. 2017 ; Layne 2023 ). This was determined based on Z-score values (Jain et al. 2015 ). Climate characterization could help to identify the potential and risks, which could help researchers to understand existing limitations to cropping systems, as well as to plan for better short- and long-term adaptation strategies under various management and climatic conditions. Detailed climate characterization that integrates the occurrence of drought, rainfall frequency and distribution for the long-term growing season, probabilities of the rain onset, and optimized planting dates has not been adequately documented for Senegal and Burkina Faso; thus, it needs attention. Maize ( Zea mays L.), pearl millet ( Pennisetum glaucum L. R. Br.), sorghum ( Sorghum bicolor L. Moench), and peanut ( Arachis hypogaea L.) are the major crops in Senegal and Burkina Faso. The yield of these crops has been reduced partly due to climate variability (Araya et al. 2022 ). Crop failure due to climate risk can be minimized using various agronomic and water management techniques (Araya and Stroosnijder 2010 ; 2011 ; Araya et al. 2019 ; Araya et al. 2021 ). Resource-scarce farmers in Africa require efficient water management strategies to mitigate climatic risk (Silungwe et al. 2018 ). Erratic rainfall distribution during the growing season (dry spells) could reduce crop productivity in the region (Araya and Stroosnijder 2011 ; Araya et al. 2012 ). Knowledge of the number of rainy days, rain onset, and the length of the growing season is important to make strategic decisions for optimal management of resources and to reduce the risk of crop failure (Araya and Stroosnijder 2011 ; Araya et al. 2012 ). There are many techniques for evaluating the onset and cessation of rainfall for a given location; among others, the FAO ( 1980 ) approach has been used by many researchers. The difference in rain onset and optimal planting dates varies by location, crop, and cultivar characteristics. Crop simulation models help in optimizing planting dates for different locations and crops. We hypothesize that optimal planting dates could be evaluated using a crop model based on three rainfall onset probabilities (30%, 50%, and 70%) of satisfying crop water demand developed from the relationship between rainfall and reference evapotranspiration. Thus, in this study, the method presented in FAO ( 1980 ) was further evaluated for assessing optimal planting dates using a crop simulation model at various onset occurrence probabilities for selected locations in Burkina Faso and Senegal. The specific objectives of this study were to (i) characterize the climate and assess the occurrence of meteorologically below-average rainfall years, (ii) evaluate the rain onset, cessation, and length of growing period, and (iii) study the optimal planting time for major crops such as maize, millet, and peanuts in Burkina Faso and Senegal. 2. Materials and methods 2.1 Study sites The study was conducted for selected 10 and 12 locations in Burkina Faso and Senegal, respectively (Fig. 1 a, b). The selection criteria for the locations consider the distances between them and rainfall gradient. The range of elevation for more than 80% of its area is between 250 and 300 m (Dembélé and Zwart 2016 ). The climatic seasons for Burkina Faso are classified as dry (October to April) and wet season (May to September). The annual rainfall ranges between 300 and 1200 mm, with the lowest and highest values corresponding to northern and southern Burkina Faso, respectively (Dembélé and Zwart 2016 ) (Fig. 1 a). The average baseline (1981–2020) maximum and minimum temperatures of the growing season for the selected locations in Burkina Faso range from 31.2 to 35.7°C and 22.2 to 24.2°C, respectively (Fig. S1 a). Agro-climatologically, Burkina Faso is classified into three regions: Sudanian (southern part, humid savannah, with rainfall > 900 mm), Sudano-Sahelian (central, arid savannah, rainfall 600 to 900 mm), and Sahelian (northern, rainfall < 600 mm) zones (Dabiré et al. 2012 ; Gaisberger et al. 2017 ). Similarly, Senegal is located in West Africa (Fig. 1 b) with an average elevation of 69 m ( https://www.worlddata.info/africa/senegal/index.php ). Like Burkina Faso, the months of October to April and May to September are the dry and wet seasons for Senegal, respectively. The annual rainfall ranges between 200 and > 1100 mm, with the lowest and highest values corresponding to northern and southern Senegal, respectively (Fig. 1 b). The mean highest and lowest temperatures for the chosen Senegalese areas during the growing season range from 32 to 37°C and 23 to 25°C, respectively, based on the average baseline (1981–2020). Senegal's mean growing season high and low temperatures are displayed in Fig. S1 b. Senegal shares the same agro-climatic zones as Burkina Faso, with similar rainfall patterns, despite the fact that the northern half of Senegal is drier than the northern part of Burkina Faso. 2.2 Climate data and analysis Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) provided the daily rainfall data for 1981–2020 (Funk et al. 2014 ; 2015 ; Dinku et al. 2018 ). Figures 1 a and b show the annual rainfall in Senegal and Burkina Faso. The number of wet days with rainfall values of ≥ 5 and ≥ 10 mm was calculated for the long-term growth seasons (1981–2020). The rainy days with rainfall values ≥ 5 and ≥ 10 mm were presented on a weekly basis for the period 1981–2020, analyzed, and plotted at three probability exceedance levels (30, 50, and 70%). In addition, anomalies of annual rainfall variabilities and Z scores were analyzed and plotted, and meteorologically below-average rainfall years were evaluated for both Burkina Faso and Senegal. Z scores of below − 1 were considered as meteorological drought years (Jain et al. 2015 ). 2.3 Rain onset, cessation and length of growing period The weekly sum of rainfall and reference evapotranspiration for the period 1981–2020 was calculated. Three exceedance probability levels of weekly rainfall (30%, 50%, and 70%) were calculated and plotted along with the weekly sum of reference evapotranspiration to generate three onsets of rain (hereafter mentioned as P1 for 30%, P2 for 50%, and P3 for 70%) based on FAO ( 1980 ). The relationships of the cumulative weekly rainfall and reference evapotranspiration were used for estimating the onset and cessation of rain because (i) most of the soils in both Burkina Faso and Senegal are dominantly coarse-textured, which might cause substantial water stress if any time longer than a week is used; and (ii) it was set up to onset week rather than onset date because onset week is more reliable than onset date. However, some crops in some locations might require earlier planting, such as those dry planting practices in northern Ethiopia (Araya et al. 2012 ). Therefore, for comprehensive analysis, the onset of rainfall under three rainfall probabilities of exceedance (30, 50, and 70%) was evaluated and presented. The time at which the weekly rainfall total under the three probabilities (P1, P2, and P3) equals or exceeds 50% of the weekly reference evapotranspiration is considered the start (onset) of rain. On the other hand, the week at the end of the growing season when half of the weekly reference evapotranspiration falls below the weekly rainfall is known as the cessation date. According to FAO ( 1980 ), LGP is the difference between the dates of the beginning and end of the growing season. For Burkina Faso and Senegal, onset, cessation, and LGP were thus geographically depicted. Early, normal, and late onset of rain, respectively, would result from adopting onset based on P1, P2, and P3. However, the Decision Support System for Agrotechnology Cropping System Model (DSSAT) version 4.75 was used to assess the best planting based on the three onset probabilities that produced a high yield (Hoogenboom et al. 2019 ). The days to maturity (dm) and crop evapotranspiration changes were calculated by subtracting the baseline from the future, dividing by the baseline, and multiplying by 100 (Eq. 1). dm = \(\:\left[\frac{\text{F}\text{m}-\text{B}\text{m}}{\text{B}\text{m}}\right]\text{*}100\) Eq. 1 dm, is days to maturity deviation; Fm, future days to maturity; Bm, baseline days to maturity. 2.4 Model simulation setup The DSSAT model (Hoogenboom et al. 2019 ) was used to simulate the yield of dominant crops in selected locations in Burkina Faso and Senegal. Selected crops for Burkina Faso were maize, pearl millet, sorghum, and peanut, whereas selected crops for Senegal were millet, sorghum, and peanut. The simulations were carried out based on prior calibrated and validated models for the cultivars as presented in Singh et al. ( 2014 ; 2018) and Jha et al. ( 2021 ) for sorghum (CSM-335) and millet (CIVT) genotypes and Sarr and Camara ( 2018 ) and Araya et al. ( 2022 ) for peanut cultivar (Virginia 897). The soil types used for Burkina Faso and Senegal are presented in Tables S1 and S2. The soil information for Burkina Faso was obtained from Nyamekye et al. ( 2018 ). Similar soils in the DSSAT database were obtained (IBSB 910009, IBSB 910017, and IUBF 9701110) and used in this study (Table S1 ). Similarly, a dominant soil for Senegal from the DSSAT database (IBML910001) was used as presented in Araya et al. ( 2022 ). The management includes application of 68 kg N/ha based on prevalent practices (Jha et al. 2021 ; Araya et al. 2022 ). Optimal planting by crop type and yield simulations based on three rain onset probabilities (P1, P2, and P3) were evaluated. In addition, in order to understand the impacts of rain on the performance of crops, growing season rainfall (planting to harvest) was regressed against simulated maize yield. Only maize was selected for the analysis due to its sensitivity to water stress. 2.5 Spatial analysis The yield for each location was simulated, averaged, and presented spatially across Burkina Faso and Senegal. Spatial analysis was done at the country level for the start and end of the growing season, length of the growing period, and rainy days with more than 5 and 10 mm of rain, as well as yield, using the kriging interpolation method in ArcGIS version 10.8. 3. Results and Discussion 3.1 Rainfall characteristics for Burkina Faso and Senegal The annual rainfall for Burkina Faso and Senegal decreases northwards (Fig. 1 a, b). There is unimodal rainfall with rainy periods ranging from May to September, with August as the wettest month. The southwesterly moist air mass from the Atlantic Ocean dominates and brings rain to the region in the summer, while the dry air mass from the high-pressure system above the Sahara Desert is the main air mass from November to February ( https://eros.usgs.gov/westafrica/node/157 ). The Intertropical Convergence Zone (ITCZ) moves northwards and southwards during the boreal and austral summer, respectively (Nicholson et al. 2013; Biasutti 2019 ). The ITCZ influences the rainfall intensity and duration in both countries. The ITCZ is a region of low pressure where two opposing winds—the northeasterly winds, which are dry from the Sahara, and the southwesterly winds, which are moist from the Atlantic Ocean—converge to produce rain due to thermal instability. ( https://www.earthobservatory.nasa.gov/images/703/the-intertropical-convergence-zone ). Tropical Africa experiences wet and dry seasons as a result of the ITCZ's northward movement, which reaches its northernmost point at roughly 15° N in July before moving southward in September and reaching roughly 5° S in January ( https://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03 . https://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03 ). This study showed that the rainfall amount difference in the west–east direction is smaller than in the north–south direction (Fig. 1 a, b). The annual rainfall for the northern part of Burkina Faso (440 mm) is higher than that of northern Senegal (< 215 mm). The annual rainfall in southern Burkina Faso and Senegal could reach above 1050 and 1150 mm, respectively (Fig. 1 a, b). The major reason for the decrease in rainfall from south to north is that the ITCZ stays a shorter time in the north, resulting in fewer rainy days and smaller total annual rainfall. Nicholson et al. (2013) explained that the monsoon characteristics of West Africa are a result of thermodynamic gradients (contrasts) of wind circulation between the land and ocean, which the southwesterly flow from the Atlantic Ocean brings the moisture into the continent during the boreal summer, where a heat low is developed. Rainfall variability in West Africa is associated with North-South movement of the “rain belt” (ITCZ) and intensification or weakening of the “rain belt” (ITCZ). This is controlled by changes in circulation patterns associated with the Tropical Easterly Jet, the African Easterly Jet, the low-level African Westerly Jet, and the Saharan Heat Low (Nicholson et al. 2013). Most importantly, temperature and pressure conditions over the Atlantic and the intensity of the Tropical Easterly Jet over West Africa are considered as major contributors. Nicholson and Grist ( 2003 ) and Nicholson et al. (2013) reviewed the circulation features of the West African monsoon, including the upper-level Tropical Easterly Jet, the mid-level African Easterly Jet, and low-level southwesterly flow. 3.2 Meteorologically below average rainfall years For Burkina Faso, meteorological below-average rainfall occurred in the 1980s (1981–1987) (Figs. S2a-j, S3a-j). The severity of these years in Burkina Faso slightly varied by location (Figs. S2, S3). Of the 1980s meteorologically below-average rainfall years, the most severe and common among all locations was the meteorological drought that occurred in 1983–84 (Figs. S2a-j, S3a-j). In Burkina Faso, the most severe drought occurred in the years 1972 to 1973 and 1984 to 1985, which caused the death of animals and people (Dembélé and Zwart 2016 ). The 1980s drought severity was more pronounced in already drier locations like Diro and Djibo. The reduction in annual rainfall and rainy days above 5 mm for most locations ranged between 25 and 35% (Figs. S2a-j, S3a-j). This annual rainfall reduction in the 1980s was above 1.5 standard deviations for most of the locations (Fig. S3a-j). Nicholson et al. (2013) reported major droughts occurred in the 1970s and 1980s in West Africa. These droughts were associated with changes in sea surface temperatures (Biasutti 2019 ). After the 1980s drought, rainfall in the region recovered, but the pattern became more intense and wet towards the late rainy season (Biasutti 2019 ). Burkina Faso and Senegal's recovered rainfall annual totals were displayed in Figs. S2-3, which depicted rainfall anomalies. Though there were a few moderate droughts (below normal) in the 1990s and 2000s as well, the 1980s drought was more severe than the decades that followed. For example, some locations in Burkina Faso experienced different levels of severity (severe to mild) in 1990, 1992, 1993, 1996, and 1997. This analysis demonstrated that following the 1990s, there were fewer years with rainfall that was below average. After 2000, only a small number of years that differed by location were observed. For Burkina Faso, mild to severe meteorologically below-average rainfall years (meteorological drought years) were observed in at least 6 out of 40 years, or 15% (with substantial spatial variation) of the years during the period 1981–2020. Studies indicated that rainfall after the 1980s has increased, although intraseasonal dry spells might have occurred, which could reduce yields (Roudier et al. 2011 ; Sylla et al. 2016; Sultan and Gaetani 2016). Senegal and Burkina Faso both experienced years with rainfall that was below average. The severity of these years varied by location, but for the most part, the 1980s were also severe in Senegal, as in Burkina Faso. The annual rainfall reduction was more than 25% for most of the locations. The severity was also much more pronounced in the north than in the south, as the rain was already climatologically drier than the south. The years 1983–84 were the driest of all. Location-specific variations in the severity of the years with rainfall below average included 1981–1986, 1990–1992, and 1996–1998 (Figs. S4a-j, S5a-j). The years 1993–1995 were normal or above average years. In addition, the years 2006–2007, 2014, 2017, and 2019 were meteorologically below average rainfall years for the majority of the locations, although the severity varied by location. Overall, for the past 40-year period, at least 6 years (15%) were taken as meteorological drought years whose severity (mild to severe) could vary depending on the location and year. The years between 2000 and 2020 were more normal and above normal years with few years of mild meteorological drought (Figs. S4a-j, S5a-j). 3.3 Rainy days of above 5 and 10 mm The probabilities of exceedance of the number of rainy days with rainfall values ≥ 5 and ≥ 10 mm rainfall for the different locations varied substantially (Fig. 2 a-d; Figs. S6a, b and 7a, b). There were large differences between the number of rainy days with rainfall values ≥ 5 and ≥ 10 mm for 30 and 70% probabilities of occurrences. In most locations, the probabilities of occurrence of rainy days with rainfall values ≥ 5 or ≥ 10 mm based on 50 and 70% probabilities were not different. This shows that in three out of four years, the number of rainy days with rainfall values ≥ 5 and ≥ 10 mm were stable for each station (especially after 1990, the number of rainfall events and amount received in the locations were stabilized). In the case of Burkina Faso, the lowest was observed for Djibo, which is in the north, while the highest was observed for Gaoua and Bonfora, which are in the south of Burkina Faso (Fig. 2 a, b; Figs. S6a, b). For Burkina Faso, the average number of rainy days with rainfall values ≥ 5 and ≥ 10 mm ranged between 30 to 72 and 15 to 39 days, respectively (Fig. 2 a, b; Fig. S6a, b). Similarly, for Senegal, the lowest number of rainy days with rainfall values ≥ 5 and ≥ 10 mm were found in northern Senegal (i.e., Podor and Dagana), while the highest were found in southern Senegal (i.e., Kold and Keudougou) (Fig. 2 c, d; Figs. S7a, b). The number of rainy days with rainfall values ≥ 5 and ≥ 10 mm ranged from 15 to 72 and 7 to 45 days, respectively (Fig. 2 c, d; Figs. S7a, b). The number of rainy days with rainfall values ≥ 5 or ≥ 10 mm for each growing season in both Burkina Faso and Senegal was well correlated with the annual total rainfall (Figs. S8a-i). The number of rainy days decreased during the drought and increased during wet years (not shown). In both countries, the number of rainy days increases from north to south. 3.4 Onset, cessation of rain and LGP Time of rain onset represents the start of the growing (rainy) season, although sometimes there could be risks of dry spells (that could cause germination failure due to false start) (Araya et al. 2012 ). Three rain onset probabilities were assessed in this investigation (Fig. S9a-h): (i) weekly cumulative rainfall probabilities in one out of three years meeting 50% weekly cumulative reference evapotranspiration (P1); (ii) weekly cumulative rainfall in one out of two years meeting at least 50% weekly cumulative reference evapotranspiration (P2); and (iii) weekly cumulative rainfall probabilities in three out of four years meeting 50% weekly cumulative reference evapotranspiration (P3). Considering P2, the earliest and latest rain onset for Burkina Faso corresponded to standard weeks 17 to 23 and 25 to 27, respectively (Fig. S10a). The locations with the later cessation of rain were those with the earliest beginning (Fig. S10a, b), which are found in the south, while places with late rain onset corresponded to early rain cessation, which are found in the northern part of the country (Fig. S10a, b). For Senegal, the earliest onset ranged between standard weeks 22 and 24 (Fig. S10c), which is slightly later than Burkina Faso. Pre-onset for the Sahel for the period 1968–1990 occurred around the middle of May (Sultan and Janicot 2003 ). Early planting has some challenges, such as failure of germination due to longer dry spells (Araya et al. 2012 ). The second option is the 70–75% onset (P3) (probability of onset occurrence in three out of four years), which could be more reliable for seedling germination than P2 (Fig. 3 a, c) because it is based on meeting criteria that the cumulative rain be equal to or above the corresponding 50% weekly cumulative reference evapotranspiration in three out of four years. According to this onset strategy, Burkina Faso onset corresponded to standard weeks 20 to 23.9 in the south, 24 to 27.6 in the center, and 27.7 to 29.5 in the north, respectively (Fig. 3 a). Whereas the cessation ranged from standard week number 38–40 in the north, 40–41 in the center, and 41–43 in the south (Fig. 3 b). Similarly, for Senegal, the 70–75% onset could range from week number 24–25.5 in the south, 25.6–28.5 in the center, and 28.6–33 in the north (Fig. 3 c). The cessation for both Burkina Faso and Senegal is presented in Fig. 3 b and d. The advantage with this strategy is that replanting due to germination failure could be reduced, but the disadvantage is that it could further shorten the growing period in locations where their rainy periods are already short, like northern Burkina Faso and Senegal, which could lead to total crop loss or significant yield reduction. In addition, some late-maturing or drought-tolerant crops might require earlier planting to give high yield, which might be another disadvantages of this approach. Waongo ( 2015 ) reported a dry spell of 7 days was greater in northern than in southern Burkina Faso, with a relatively higher risk of occurrence in May (> 20%). The risk of a dry spell > 10 days in July decreases to less than 20% (Waongo 2015 ). In this study, the optimal planting time is the period when yield is maximized as simulated using the crop model. The crops gave a relatively higher yield at onset derived based on rainfall probabilities of an exceedance level of 70%. According to Sultan and Janicot ( 2003 ), there was no correlation among the pre-onset dates, onset dates, and seasonal sum of rainfall for the Sahel for the climatic period 1968 to 1990, but it is more related to shifts in the ITCZ. As defined above, the LGP in this study is the difference between the onset and cessation of seasonal rainfall during the growing season. Assuming onset (P2, 50% probability), the LGP for both Burkina Faso and Senegal increases from north to south with a maximum of 170 days for Burkina Faso and 133 days for Senegal (Fig. 4 a and b). The LGP result for Burkina Faso strongly agreed with Waongo ( 2015 ). The LGP for central and northern Burkina Faso ranged from 100 to 135 and 63 to 99 days, respectively (Fig. 4 a). The corresponding LGP values for central and northern Senegal were 74 to 113 days and 14 to 73 days, respectively (Fig. 4 b). The northern most part of Senegal received a maximum of 25 rainy days of above 5 mm with a maximum LGP of 53 days, which could make it difficult to grow crops under this climate condition unless supplemented with irrigation (Fig. 4 b). Assuming onset (P3, 70% probability), the LGP for Burkina Faso and Senegal ranged from 60 to 157 days and 21 to 126 days, respectively (Fig. 4 c, d). The shortest and longest LGP corresponded to the northern and southern parts of the countries, respectively. The LGP for northern Burkina Faso and Senegal ranged from 60 to 76 and 21 to 39 days, respectively. Based on the analysis of the growing period, northern Senegal is not suitable for rainfed agriculture, while some drought-resistant, short-maturing cultivars might be grown in northern Burkina Faso. 3.5 Evaluation of optimal planting date In this study, we used yield as a measure of optimal planting. Yields of the major crops across the different locations were simulated based on three levels of onset probability exceedance (P1, P2, and P3) (Fig. S11a-d). Results showed that the large majority of southern Burkina Faso and Senegal gave better yields under 70% (P3) when compared to 50% (P2) or 30% (P1) onset probabilities. The optimal planting date for maize, peanuts, and millet corresponded to P3 (Fig. S11a-c). In contrast, the optimal planting date for sorghum corresponded to P1 (Fig. S11d). The 70% onset probabilities were more reliable for growing water-stress-sensitive crops such as maize, which could reduce possibilities of crop failure at germination. In addition, the LGP matches well with the growing cycle of the selected crops, although the LGP shortens under P3 compared to P2. The length of the growing season shortened from a maximum of 170 days under 50% probabilities of onset to 157 days under 70% probabilities (Fig. 4 a and c). Based on the planting strategies, planting should start earlier in southern Burkina Faso and Senegal than the rest of each country, and planting based on P3 (70% probabilities of onset) gave higher yield. Waongo et al. (2013) reported the optimal planting date for Burkina Faso varied by location, with the earliest and latest planting for southern and northern Burkina Faso, respectively. The spatial yield levels for maize, peanuts, millet, and sorghum across Burkina Faso are presented in Fig. 5 a-d. The yield level for the major crops follows the rainfall gradient across Burkina Faso. Yield level increased southwards, which could be due to a longer rainy period and a higher amount of rainfall in the south than in the north or central part of the country. The spatial yields for millet, peanut, and sorghum for Senegal are presented in Fig. 6 a-c. Like Burkina Faso, the yield level increases with rainfall gradient across the country (yield increases from north to south). Use of optimal planting dates is less costly, which could be used as an adaptation measure for enhancing yield in Western African countries. In this study, we found that planting maize, peanuts, and millet when the 70% probability of exceedance of rainfall crosses the 50% reference evapotranspiration would be optimal. The optimal planting date was reported to be between May 1 in the southwest and July 11 in northern Burkina Faso, which varies depending on location, although planting in May is considered risky (Waongo 2015 ). The growing period can be increased by using earlier planting. The optimal planting time for the northern part is when the ITCZ reaches its northernmost position, during which rainfall is intense (crop failure is less likely at the time of germination). Accordingly, our analysis shows that rainfall played a significant role in modifying yield across the two countries. The relationship between maize yield and precipitation from planting to harvest is presented in Fig. S12a-j. There were moderately weak (R² = 0.4 to 0.58) to strong (R² = 0.64 to 0.75) relationships between yield and precipitation. Although rainfall played a substantial role in maize yield, the influence of the rise in temperature on yield should not be underestimated. The shortening of crop growing period could reduce accumulation of assimilates and yield (Hasanuzzaman et al. 2013 ). Roudier et al. ( 2011 ) reported a larger yield decline because of temperature increase than rainfall changes. The rise in temperatures along with an increase in rainfall in the eastern Sahel and a decrease in rainfall in the western Sahel resulted in a decrease in agricultural production by 50 kg per capita (Defrance et al. 2020 ). Crop yield in West Africa could decline with a median decrease of 11% and more negative (-18%) results towards the north (Sudano-Sahelian) compared to the south (Guinea) (Roudier et al. 2011 ). Sultan and Gaetani (2016) projected yield reduction for West Africa. Agriculture in the Sudano-Sahelian zone of West Africa is expected to be impacted by climate change (Sultan and Gaetani 2016; Roudier et al. 2011 ). West Africa is vulnerable to climate risks because it depends on rainfed agriculture with little adaptation capacity (such as economic and institutional) (Sultan and Gaetani 2016). 4. Conclusions Most of the meteorological drought occurred in Burkina Faso and Senegal before 1992. At least 15% of the past 40 years (1981–2020) were meteorologically below-average rainfall years. The most severe meteorological drought occurred (in Senegal and Burkina Faso) in 1983–84. During the most severe drought years, annual rainfall for most locations decreased by more than 25% of the long-term mean. The probabilities of occurrence of rainy days equal to or above 5 mm for Burkina Faso and Senegal in one out of two years and in three out of four years were not different, indicating the rainfall was stable for the majority of the years after 1990. The average number of rainy days equal to or above 5 and 10 mm ranged between 30 and 72 and 15 and 39 days, respectively, for Burkina Faso and 15 and 72 and 7 and 45 days, respectively, for Senegal. The lowest and highest number of rainy days corresponded to northern and southern locations, respectively. It is risky to grow crops under rainfed conditions in northern Burkina Faso and Senegal, where rainy days above 5 mm are limited to less than 30 days. These areas might be more suitable for growing forage grasses (animal feed or crops that do not need to harvest grains) than for grain crops. For most locations (except the north), our results showed that P3 (onset generated based on weekly cumulative rainfall probabilities approximately in three out of four years meeting 50% weekly cumulative reference evapotranspiration) is more reliable than P2 (onset generated from weekly cumulative rainfall in one out of two years meeting at least the 50% weekly cumulative reference evapotranspiration) or P1 (onset generated based on weekly cumulative rainfall probabilities in one out of three years meeting 50% weekly cumulative reference evapotranspiration). However, it should be understood that P3 could shorten the growing period for late-maturing cultivars in locations that have short growing seasons, such as those in northern Burkina Faso and Senegal. For late-maturing cultivars, using P2 could be considered more suitable than P3 or P1. Using P3 has the advantage of reducing false starts/failures at germination or reduces replanting. However, in northern Burkina Faso and Senegal, the yield of all crops improved under P1 when compared to P2 or P3 because of the short LGP. On the other hand, sorghum yield was improved under P1 when compared to P2 or P3, attributed to its relative drought tolerance compared to other crops. Declarations Statements Conflict of Interest All authors declared that no conflict or competing interest or personal relationships to influence the work in any way or form. All authors read and approved the submission of this manuscript. Author Contribution A. Araya: Conceptualization, Investigation, Methodology, Writing original draft; P.V.V. Prasad: Conceptualization, Methodology, Funding acquisition, Resources, Project administration, Visualization, Writing—review & editing; P.K. Jha: Investigation, Formal analysis, Visualization, Writing—review & editing; I.A. Ciampitti: Investigation, Resources, Writing—review & editing; V. Sharda: Writing—review & editing. All authors reviewed the manuscript. Acknowledgement We thank the Feed the Future Innovation Lab for Collaborative Research on Sustainable Intensification (Grant no. AID-OAA-L-14-00006) at Kansas State University funded by the United States Agency for International Development for supporting this activity. The contents of this publication are the sole responsibility of the authors and do not reflect the views of funding agencies and representing organizations. Contribution no. 25-190-J from the Kansas Agricultural Experiment Station. Data Availability Datasets used in this research are available upon reasonable request and time (please contact the corresponding author). References Araya A, Stroosnijder L (2011) Assessing drought risk and irrigation need in northern Ethiopia. Agric For Meteorol 151:425–436. https://doi.org/10.1016/j.agrformet.2010.11.014 Araya A, Stroosnijder L (2010) Effects of tied ridges and mulch on barley ( Hordeum vulgare ) rainwater use efficiency and production in Northern Ethiopia. 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Accessed on Aug. 2023 Maguèye M, Ndao ML (2013) Climate risk and food security in Senegal: Analysis of climate. WFP CCAF ANACIM IRI Nicholson SE (2013) The West African Sahel: A Review of recent studies on the rainfall Regime and its interannual variability. Hindawi Publishing Corporation ISRN Meteorol 453521:32. http://dx.doi.org/10.1155/2013/453521 Nicholson SE, Grist JP (2003) The seasonal evolution of the atmospheric circulation over West Africa and equatorial Africa. J Clim 16:1013–1030. https://doi.org/10.1175/1520-0442 Nyamekye C, Thiel M, Schönbrodt-Stitt S, Zoungrana B, Amekudzi L (2018) Soil and water conservation in Burkina Faso West Africa. Sustainability 10:3182. https://doi.org/10.3390/su10093182 Roudier P, Muller B, Aquino PD, Roncoli C, Soumaré MA, Batté L, Sultan B (2014) The role of climate forecasts in smallholder agriculture: Lessons from participatory research in two communities in Senegal. Clim Risk Manage 2:42–55. https://doi.org/10.1016/j.crm.2014.02.001 Roudier P, Sultan B, Quirion P, Baron C, Alhassane A, Traoré S, Muller B (2011) An ex-ante evaluation of the use of seasonal climate forecasts for millet growers in SW Niger. Int J Climatol 32(5):759–771. https://doi.org/10.1002/joc.2308 Sarr AB, Camara M (2018) Simulation of the impact of climate change on peanut yield in Senegal. Int J Physic Sci 13(5):79–89. https://doi.org/10.5897/IJPS2017.4710 Silungwe FR, Graef F, Bellingrath-Kimura SD, Tumbo SD, Kahimba FC, Lana MA (2018) Crop upgrading strategies and modelling for rainfed cereals in a semi-arid climate - a review. Water 10:356. https://doi.org/10.3390/w10040356 Singh P, Nedumaran S, Traore PCS, Boote KJ, Rattunde HFW, Prasad PVV, Singh NP, Srinivas K, Bantilan MCS (2014) Quantifying potential benefits of drought and heat tolerance in rainy season sorghum for adapting to climate change. Agricultural For Meteorol 185:37–48. https://doi.org/10.1016/j.agrformet.2013.10.012 Singh P, Boote KJ, Kadiyala MDM, Nedumaran S, Gupta SK, Srinivas K, Bantilan MCS (2017) An assessment of yield gains under climate change due to genetic modification of pearl millet. Sci Total Environ 601:1226–1237. https://doi.org/10.1016/j.scitotenv.2017.06.002 Sultan B, Roudier P, Quirion P, Alhassane A, Muller B, Dingkuhn M, Ciais P, Guimberteau M, Traore S, Baron C (2013) Assessing climate change impacts on sorghum and millet yields in the Sudanian and Sahelian savannas of West Africa. Environ Res Let 8:014040. https://doi.org/10.1088/1748-9326/8/1/014040 Sultan B, Janicot S (2003) The West African Monsoon Dynamics. Part II: The ‘‘Preonset’’ and ‘‘Onset’’ of the Summer Monsoon. 16. 2003 American Meteorological Society. FAO, 1980. Report on the Agro Ecological Zones Project. 48/4. Food and Agricultural Organization. Rome, Italy Sylla MB, Pal JS, Faye A, Dimobe K, Kunstmann H (2018) Climate change to severely impact West African basin scale irrigation in 2°C and 1.5°C global warming scenarios. Sci Rep 8:14395. https://doi.org/10.1038/s41598-018-32736-0 Waongo M (2015) Optimizing Planting Dates for Agricultural Decision-Making under Climate Change over Burkina Faso/West Africa. PhD dissertation. University of Augsburg. Germany Additional Declarations No competing interests reported. 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As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7180722","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":497890946,"identity":"4f90a9fa-13ba-4aae-b042-6145a19fd1ff","order_by":0,"name":"A. 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Prasad","email":"","orcid":"","institution":"Kansas State University","correspondingAuthor":false,"prefix":"","firstName":"P.","middleName":"V.V.","lastName":"Prasad","suffix":""}],"badges":[],"createdAt":"2025-07-21 20:38:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7180722/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7180722/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00704-025-05936-8","type":"published","date":"2025-12-05T15:58:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88816498,"identity":"531d0654-2d28-4b0c-8048-446e96851718","added_by":"auto","created_at":"2025-08-11 16:27:01","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":152267,"visible":true,"origin":"","legend":"\u003cp\u003eStudy locations and spatial ranges of annual rainfall for Burkina Faso (a) and Senegal (b)\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/9a8f7d2d28f3156a480f8174.png"},{"id":88816499,"identity":"44e691fe-20a6-4f0c-bda2-84ae589add38","added_by":"auto","created_at":"2025-08-11 16:27:01","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":276866,"visible":true,"origin":"","legend":"\u003cp\u003eAverage rain days above 5 mm (a) and rain days above 10 mm (b) for Burkina Faso locations and average rain days above 5 mm (c) and rain days above 10 mm (d) for Senegal locations based on climate data for the period of 1981–2020.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/cca39ca6af333bc2e16cb5d0.png"},{"id":88815168,"identity":"ca8676ae-6b2c-4dd3-b3a1-81225d56f3e7","added_by":"auto","created_at":"2025-08-11 16:11:01","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":216846,"visible":true,"origin":"","legend":"\u003cp\u003eAverage onset based on 70% rain onset (P3) (a) and cessation (b) for Burkina Faso locations; and P3 (c) and cessation (d) for Senegal based on climate data for the period of 1981–2020.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/4bb6d53b0335e88c2d039a62.png"},{"id":88815171,"identity":"1c15af9d-bc05-428f-93a7-e6a8f24b7730","added_by":"auto","created_at":"2025-08-11 16:11:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":248549,"visible":true,"origin":"","legend":"\u003cp\u003eAverage length of growing period (LGP) based on onset P2 (a) and P3 (c) for Burkina Faso and based on onset P2 (b) and P3 (d) for Senegal for the period of 1981–2020. Note that P2 is onset generated from weekly cumulative rainfall in one out of two years meeting at least the 50% weekly cumulative reference evapotranspiration. P3 is onset generated based weekly cumulative probabilities in three out of four years meeting 50% weekly cumulative reference evapotranspiration.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/1c804eec91c85832067345db.png"},{"id":88815556,"identity":"9d78f2a9-72db-4442-9755-12fc72829f4f","added_by":"auto","created_at":"2025-08-11 16:19:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":324012,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial yield of maize (a), millet (b), peanut (c) and sorghum (d) for different locations and regions in Burkina Faso.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/330109d73f32f022dedb18e3.png"},{"id":88816500,"identity":"7902b2a3-37ae-48a5-8a17-b5afb557d5f8","added_by":"auto","created_at":"2025-08-11 16:27:01","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":246440,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial yield of millet (a), peanut (b) and sorghum (c) for different locations and regions in Senegal.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/b87e4fa8215f6f354916c160.png"},{"id":97724214,"identity":"fd66bc93-5a1c-4a6f-873b-15f7d842d9cb","added_by":"auto","created_at":"2025-12-08 16:12:15","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1828698,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/820f3f6b-3b72-4b89-a035-8eea0a4bbd56.pdf"},{"id":88815553,"identity":"31b6274e-6b6b-4bdb-b8d7-1902ca0484b1","added_by":"auto","created_at":"2025-08-11 16:19:01","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1904044,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryTablesandFigures07212025.docx","url":"https://assets-eu.researchsquare.com/files/rs-7180722/v1/dc8a7c26251055f23f218d07.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Agroclimatic analysis for reducing planting risks in Burkina Faso and Senegal","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eClimate variabilities remain a risk factor and challenge for agri-food systems. Agriculture is susceptible to climate variability and change. Agriculture in most of the semi-arid and arid countries, particularly in Africa, depends on rainfall (rainfed agriculture), which is influenced by climatic variability and seasonal weather changes (Magu\u0026egrave;ye and Ndao \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). As such, with limited irrigation, technology adoption, and economic and institutional infrastructure, African agriculture is vulnerable to climate variability and changes (Sultan and Gaetani 2016; Sylla et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Global surface temperatures increased between 0.95 and 1.2\u0026deg;C during the period 2010\u0026ndash;2020 relative to the preindustrial era (1850\u0026ndash;1900) (Arias et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and are expected to increase under future scenarios (Sylla et al. 2016). Rainfall and seasonal temperature play a significant role in crop production, particularly in the length of the growing season (LGP) in West Africa (Roudier et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Magu\u0026egrave;ye and Ndao \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Understanding the adverse effects of rainfall and temperature on the LGP, crop evapotranspiration, and optimal planting date would be critical and important for developing climate-resilient strategies and assisting farmers to understand the possible impacts and address the problem in a timely and cost-effective manner.\u003c/p\u003e\u003cp\u003eDrought is one of the major challenges in West Africa, especially in the 1970s and 1980s (Dabir\u0026eacute; et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Demb\u0026eacute;l\u0026eacute; and Zwart \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Sultan and Gaetani 2016). The north-central and northern Burkina Faso and Senegal are susceptible to climate variability and change (Defrance et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Characterizing the rainfall that includes rainfall distribution, frequency, and the severity of meteorological drought could be useful to understand the impacts on crop production and develop crop suitability for a region. In this study, meteorological drought refers to a season during which the received sum of rainfall falls below normal when compared to the long-term average (Harpold et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Layne \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This was determined based on Z-score values (Jain et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Climate characterization could help to identify the potential and risks, which could help researchers to understand existing limitations to cropping systems, as well as to plan for better short- and long-term adaptation strategies under various management and climatic conditions. Detailed climate characterization that integrates the occurrence of drought, rainfall frequency and distribution for the long-term growing season, probabilities of the rain onset, and optimized planting dates has not been adequately documented for Senegal and Burkina Faso; thus, it needs attention.\u003c/p\u003e\u003cp\u003eMaize (\u003cem\u003eZea mays\u003c/em\u003e L.), pearl millet (\u003cem\u003ePennisetum glaucum\u003c/em\u003e L. R. Br.), sorghum (\u003cem\u003eSorghum bicolor\u003c/em\u003e L. Moench), and peanut (\u003cem\u003eArachis hypogaea\u003c/em\u003e L.) are the major crops in Senegal and Burkina Faso. The yield of these crops has been reduced partly due to climate variability (Araya et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Crop failure due to climate risk can be minimized using various agronomic and water management techniques (Araya and Stroosnijder \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Araya et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Araya et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Resource-scarce farmers in Africa require efficient water management strategies to mitigate climatic risk (Silungwe et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Erratic rainfall distribution during the growing season (dry spells) could reduce crop productivity in the region (Araya and Stroosnijder \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Araya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Knowledge of the number of rainy days, rain onset, and the length of the growing season is important to make strategic decisions for optimal management of resources and to reduce the risk of crop failure (Araya and Stroosnijder \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Araya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). There are many techniques for evaluating the onset and cessation of rainfall for a given location; among others, the FAO (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1980\u003c/span\u003e) approach has been used by many researchers. The difference in rain onset and optimal planting dates varies by location, crop, and cultivar characteristics. Crop simulation models help in optimizing planting dates for different locations and crops. We hypothesize that optimal planting dates could be evaluated using a crop model based on three rainfall onset probabilities (30%, 50%, and 70%) of satisfying crop water demand developed from the relationship between rainfall and reference evapotranspiration. Thus, in this study, the method presented in FAO (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1980\u003c/span\u003e) was further evaluated for assessing optimal planting dates using a crop simulation model at various onset occurrence probabilities for selected locations in Burkina Faso and Senegal.\u003c/p\u003e\u003cp\u003eThe specific objectives of this study were to (i) characterize the climate and assess the occurrence of meteorologically below-average rainfall years, (ii) evaluate the rain onset, cessation, and length of growing period, and (iii) study the optimal planting time for major crops such as maize, millet, and peanuts in Burkina Faso and Senegal.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Study sites\u003c/h2\u003e\u003cp\u003eThe study was conducted for selected 10 and 12 locations in Burkina Faso and Senegal, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, b). The selection criteria for the locations consider the distances between them and rainfall gradient. The range of elevation for more than 80% of its area is between 250 and 300 m (Demb\u0026eacute;l\u0026eacute; and Zwart \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The climatic seasons for Burkina Faso are classified as dry (October to April) and wet season (May to September). The annual rainfall ranges between 300 and 1200 mm, with the lowest and highest values corresponding to northern and southern Burkina Faso, respectively (Demb\u0026eacute;l\u0026eacute; and Zwart \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The average baseline (1981\u0026ndash;2020) maximum and minimum temperatures of the growing season for the selected locations in Burkina Faso range from 31.2 to 35.7\u0026deg;C and 22.2 to 24.2\u0026deg;C, respectively (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003ea). Agro-climatologically, Burkina Faso is classified into three regions: Sudanian (southern part, humid savannah, with rainfall\u0026thinsp;\u0026gt;\u0026thinsp;900 mm), Sudano-Sahelian (central, arid savannah, rainfall 600 to 900 mm), and Sahelian (northern, rainfall\u0026thinsp;\u0026lt;\u0026thinsp;600 mm) zones (Dabir\u0026eacute; et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Gaisberger et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSimilarly, Senegal is located in West Africa (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb) with an average elevation of 69 m (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.worlddata.info/africa/senegal/index.php\u003c/span\u003e\u003cspan address=\"https://www.worlddata.info/africa/senegal/index.php\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Like Burkina Faso, the months of October to April and May to September are the dry and wet seasons for Senegal, respectively. The annual rainfall ranges between 200 and \u0026gt;\u0026thinsp;1100 mm, with the lowest and highest values corresponding to northern and southern Senegal, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The mean highest and lowest temperatures for the chosen Senegalese areas during the growing season range from 32 to 37\u0026deg;C and 23 to 25\u0026deg;C, respectively, based on the average baseline (1981\u0026ndash;2020). Senegal's mean growing season high and low temperatures are displayed in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003eb. Senegal shares the same agro-climatic zones as Burkina Faso, with similar rainfall patterns, despite the fact that the northern half of Senegal is drier than the northern part of Burkina Faso.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Climate data and analysis\u003c/h2\u003e\u003cp\u003eClimate Hazards Group Infrared Precipitation with Stations (CHIRPS) provided the daily rainfall data for 1981\u0026ndash;2020 (Funk et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Dinku et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Figures\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea and b show the annual rainfall in Senegal and Burkina Faso. The number of wet days with rainfall values of \u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm was calculated for the long-term growth seasons (1981\u0026ndash;2020). The rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm were presented on a weekly basis for the period 1981\u0026ndash;2020, analyzed, and plotted at three probability exceedance levels (30, 50, and 70%). In addition, anomalies of annual rainfall variabilities and Z scores were analyzed and plotted, and meteorologically below-average rainfall years were evaluated for both Burkina Faso and Senegal. Z scores of below \u0026minus;\u0026thinsp;1 were considered as meteorological drought years (Jain et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Rain onset, cessation and length of growing period\u003c/h2\u003e\u003cp\u003eThe weekly sum of rainfall and reference evapotranspiration for the period 1981\u0026ndash;2020 was calculated. Three exceedance probability levels of weekly rainfall (30%, 50%, and 70%) were calculated and plotted along with the weekly sum of reference evapotranspiration to generate three onsets of rain (hereafter mentioned as P1 for 30%, P2 for 50%, and P3 for 70%) based on FAO (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1980\u003c/span\u003e). The relationships of the cumulative weekly rainfall and reference evapotranspiration were used for estimating the onset and cessation of rain because (i) most of the soils in both Burkina Faso and Senegal are dominantly coarse-textured, which might cause substantial water stress if any time longer than a week is used; and (ii) it was set up to onset week rather than onset date because onset week is more reliable than onset date. However, some crops in some locations might require earlier planting, such as those dry planting practices in northern Ethiopia (Araya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Therefore, for comprehensive analysis, the onset of rainfall under three rainfall probabilities of exceedance (30, 50, and 70%) was evaluated and presented.\u003c/p\u003e\u003cp\u003eThe time at which the weekly rainfall total under the three probabilities (P1, P2, and P3) equals or exceeds 50% of the weekly reference evapotranspiration is considered the start (onset) of rain. On the other hand, the week at the end of the growing season when half of the weekly reference evapotranspiration falls below the weekly rainfall is known as the cessation date. According to FAO (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1980\u003c/span\u003e), LGP is the difference between the dates of the beginning and end of the growing season. For Burkina Faso and Senegal, onset, cessation, and LGP were thus geographically depicted. Early, normal, and late onset of rain, respectively, would result from adopting onset based on P1, P2, and P3. However, the Decision Support System for Agrotechnology Cropping System Model (DSSAT) version 4.75 was used to assess the best planting based on the three onset probabilities that produced a high yield (Hoogenboom et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe days to maturity (dm) and crop evapotranspiration changes were calculated by subtracting the baseline from the future, dividing by the baseline, and multiplying by 100 (Eq.\u0026nbsp;1).\u003c/p\u003e\u003cp\u003edm = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left[\\frac{\\text{F}\\text{m}-\\text{B}\\text{m}}{\\text{B}\\text{m}}\\right]\\text{*}100\\)\u003c/span\u003e\u003c/span\u003e Eq.\u0026nbsp;1\u003c/p\u003e\u003cp\u003edm, is days to maturity deviation; Fm, future days to maturity; Bm, baseline days to maturity.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Model simulation setup\u003c/h2\u003e\u003cp\u003eThe DSSAT model (Hoogenboom et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) was used to simulate the yield of dominant crops in selected locations in Burkina Faso and Senegal. Selected crops for Burkina Faso were maize, pearl millet, sorghum, and peanut, whereas selected crops for Senegal were millet, sorghum, and peanut. The simulations were carried out based on prior calibrated and validated models for the cultivars as presented in Singh et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; 2018) and Jha et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) for sorghum (CSM-335) and millet (CIVT) genotypes and Sarr and Camara (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Araya et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) for peanut cultivar (Virginia 897).\u003c/p\u003e\u003cp\u003eThe soil types used for Burkina Faso and Senegal are presented in Tables S1 and S2. The soil information for Burkina Faso was obtained from Nyamekye et al. (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Similar soils in the DSSAT database were obtained (IBSB 910009, IBSB 910017, and IUBF 9701110) and used in this study (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Similarly, a dominant soil for Senegal from the DSSAT database (IBML910001) was used as presented in Araya et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The management includes application of 68 kg N/ha based on prevalent practices (Jha et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Araya et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Optimal planting by crop type and yield simulations based on three rain onset probabilities (P1, P2, and P3) were evaluated. In addition, in order to understand the impacts of rain on the performance of crops, growing season rainfall (planting to harvest) was regressed against simulated maize yield. Only maize was selected for the analysis due to its sensitivity to water stress.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Spatial analysis\u003c/h2\u003e\u003cp\u003eThe yield for each location was simulated, averaged, and presented spatially across Burkina Faso and Senegal. Spatial analysis was done at the country level for the start and end of the growing season, length of the growing period, and rainy days with more than 5 and 10 mm of rain, as well as yield, using the kriging interpolation method in ArcGIS version 10.8.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Rainfall characteristics for Burkina Faso and Senegal\u003c/h2\u003e\u003cp\u003eThe annual rainfall for Burkina Faso and Senegal decreases northwards (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, b). There is unimodal rainfall with rainy periods ranging from May to September, with August as the wettest month. The southwesterly moist air mass from the Atlantic Ocean dominates and brings rain to the region in the summer, while the dry air mass from the high-pressure system above the Sahara Desert is the main air mass from November to February (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://eros.usgs.gov/westafrica/node/157\u003c/span\u003e\u003cspan address=\"https://eros.usgs.gov/westafrica/node/157\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). The Intertropical Convergence Zone (ITCZ) moves northwards and southwards during the boreal and austral summer, respectively (Nicholson et al. 2013; Biasutti \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The ITCZ influences the rainfall intensity and duration in both countries. The ITCZ is a region of low pressure where two opposing winds\u0026mdash;the northeasterly winds, which are dry from the Sahara, and the southwesterly winds, which are moist from the Atlantic Ocean\u0026mdash;converge to produce rain due to thermal instability. (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.earthobservatory.nasa.gov/images/703/the-intertropical-convergence-zone\u003c/span\u003e\u003cspan address=\"https://www.earthobservatory.nasa.gov/images/703/the-intertropical-convergence-zone\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Tropical Africa experiences wet and dry seasons as a result of the ITCZ's northward movement, which reaches its northernmost point at roughly 15\u0026deg; N in July before moving southward in September and reaching roughly 5\u0026deg; S in January\u003c/p\u003e\u003cp\u003e(\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03\u003c/span\u003e\u003cspan address=\"https://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03\u003c/span\u003e\u003cspan address=\"https://courseware.e-education.psu.edu/courses/earth105new/content/lesson07/03\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThis study showed that the rainfall amount difference in the west\u0026ndash;east direction is smaller than in the north\u0026ndash;south direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, b). The annual rainfall for the northern part of Burkina Faso (440 mm) is higher than that of northern Senegal (\u0026lt;\u0026thinsp;215 mm). The annual rainfall in southern Burkina Faso and Senegal could reach above 1050 and 1150 mm, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, b). The major reason for the decrease in rainfall from south to north is that the ITCZ stays a shorter time in the north, resulting in fewer rainy days and smaller total annual rainfall. Nicholson et al. (2013) explained that the monsoon characteristics of West Africa are a result of thermodynamic gradients (contrasts) of wind circulation between the land and ocean, which the southwesterly flow from the Atlantic Ocean brings the moisture into the continent during the boreal summer, where a heat low is developed. Rainfall variability in West Africa is associated with North-South movement of the \u0026ldquo;rain belt\u0026rdquo; (ITCZ) and intensification or weakening of the \u0026ldquo;rain belt\u0026rdquo; (ITCZ). This is controlled by changes in circulation patterns associated with the Tropical Easterly Jet, the African Easterly Jet, the low-level African Westerly Jet, and the Saharan Heat Low (Nicholson et al. 2013). Most importantly, temperature and pressure conditions over the Atlantic and the intensity of the Tropical Easterly Jet over West Africa are considered as major contributors. Nicholson and Grist (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) and Nicholson et al. (2013) reviewed the circulation features of the West African monsoon, including the upper-level Tropical Easterly Jet, the mid-level African Easterly Jet, and low-level southwesterly flow.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Meteorologically below average rainfall years\u003c/h2\u003e\u003cp\u003eFor Burkina Faso, meteorological below-average rainfall occurred in the 1980s (1981\u0026ndash;1987) (Figs. S2a-j, S3a-j). The severity of these years in Burkina Faso slightly varied by location (Figs. S2, S3). Of the 1980s meteorologically below-average rainfall years, the most severe and common among all locations was the meteorological drought that occurred in 1983\u0026ndash;84 (Figs. S2a-j, S3a-j). In Burkina Faso, the most severe drought occurred in the years 1972 to 1973 and 1984 to 1985, which caused the death of animals and people (Demb\u0026eacute;l\u0026eacute; and Zwart \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The 1980s drought severity was more pronounced in already drier locations like Diro and Djibo. The reduction in annual rainfall and rainy days above 5 mm for most locations ranged between 25 and 35% (Figs. S2a-j, S3a-j). This annual rainfall reduction in the 1980s was above 1.5 standard deviations for most of the locations (Fig. S3a-j). Nicholson et al. (2013) reported major droughts occurred in the 1970s and 1980s in West Africa. These droughts were associated with changes in sea surface temperatures (Biasutti \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). After the 1980s drought, rainfall in the region recovered, but the pattern became more intense and wet towards the late rainy season (Biasutti \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eBurkina Faso and Senegal's recovered rainfall annual totals were displayed in Figs. S2-3, which depicted rainfall anomalies. Though there were a few moderate droughts (below normal) in the 1990s and 2000s as well, the 1980s drought was more severe than the decades that followed. For example, some locations in Burkina Faso experienced different levels of severity (severe to mild) in 1990, 1992, 1993, 1996, and 1997. This analysis demonstrated that following the 1990s, there were fewer years with rainfall that was below average. After 2000, only a small number of years that differed by location were observed. For Burkina Faso, mild to severe meteorologically below-average rainfall years (meteorological drought years) were observed in at least 6 out of 40 years, or 15% (with substantial spatial variation) of the years during the period 1981\u0026ndash;2020. Studies indicated that rainfall after the 1980s has increased, although intraseasonal dry spells might have occurred, which could reduce yields (Roudier et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sylla et al. 2016; Sultan and Gaetani 2016).\u003c/p\u003e\u003cp\u003eSenegal and Burkina Faso both experienced years with rainfall that was below average. The severity of these years varied by location, but for the most part, the 1980s were also severe in Senegal, as in Burkina Faso. The annual rainfall reduction was more than 25% for most of the locations. The severity was also much more pronounced in the north than in the south, as the rain was already climatologically drier than the south. The years 1983\u0026ndash;84 were the driest of all. Location-specific variations in the severity of the years with rainfall below average included 1981\u0026ndash;1986, 1990\u0026ndash;1992, and 1996\u0026ndash;1998 (Figs. S4a-j, S5a-j). The years 1993\u0026ndash;1995 were normal or above average years. In addition, the years 2006\u0026ndash;2007, 2014, 2017, and 2019 were meteorologically below average rainfall years for the majority of the locations, although the severity varied by location. Overall, for the past 40-year period, at least 6 years (15%) were taken as meteorological drought years whose severity (mild to severe) could vary depending on the location and year. The years between 2000 and 2020 were more normal and above normal years with few years of mild meteorological drought (Figs. S4a-j, S5a-j).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Rainy days of above 5 and 10 mm\u003c/h2\u003e\u003cp\u003eThe probabilities of exceedance of the number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm rainfall for the different locations varied substantially (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-d; Figs. S6a, b and 7a, b). There were large differences between the number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm for 30 and 70% probabilities of occurrences. In most locations, the probabilities of occurrence of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 or \u0026ge;\u0026thinsp;10 mm based on 50 and 70% probabilities were not different. This shows that in three out of four years, the number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm were stable for each station (especially after 1990, the number of rainfall events and amount received in the locations were stabilized). In the case of Burkina Faso, the lowest was observed for Djibo, which is in the north, while the highest was observed for Gaoua and Bonfora, which are in the south of Burkina Faso (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b; Figs. S6a, b). For Burkina Faso, the average number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm ranged between 30 to 72 and 15 to 39 days, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b; Fig. S6a, b).\u003c/p\u003e\u003cp\u003eSimilarly, for Senegal, the lowest number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm were found in northern Senegal (i.e., Podor and Dagana), while the highest were found in southern Senegal (i.e., Kold and Keudougou) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d; Figs. S7a, b). The number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 and \u0026ge;\u0026thinsp;10 mm ranged from 15 to 72 and 7 to 45 days, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d; Figs. S7a, b). The number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 or \u0026ge;\u0026thinsp;10 mm for each growing season in both Burkina Faso and Senegal was well correlated with the annual total rainfall (Figs. S8a-i). The number of rainy days decreased during the drought and increased during wet years (not shown). In both countries, the number of rainy days increases from north to south.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Onset, cessation of rain and LGP\u003c/h2\u003e\u003cp\u003eTime of rain onset represents the start of the growing (rainy) season, although sometimes there could be risks of dry spells (that could cause germination failure due to false start) (Araya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Three rain onset probabilities were assessed in this investigation (Fig. S9a-h): (i) weekly cumulative rainfall probabilities in one out of three years meeting 50% weekly cumulative reference evapotranspiration (P1); (ii) weekly cumulative rainfall in one out of two years meeting at least 50% weekly cumulative reference evapotranspiration (P2); and (iii) weekly cumulative rainfall probabilities in three out of four years meeting 50% weekly cumulative reference evapotranspiration (P3). Considering P2, the earliest and latest rain onset for Burkina Faso corresponded to standard weeks 17 to 23 and 25 to 27, respectively (Fig. S10a). The locations with the later cessation of rain were those with the earliest beginning (Fig. S10a, b), which are found in the south, while places with late rain onset corresponded to early rain cessation, which are found in the northern part of the country (Fig. S10a, b). For Senegal, the earliest onset ranged between standard weeks 22 and 24 (Fig. S10c), which is slightly later than Burkina Faso. Pre-onset for the Sahel for the period 1968\u0026ndash;1990 occurred around the middle of May (Sultan and Janicot \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Early planting has some challenges, such as failure of germination due to longer dry spells (Araya et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe second option is the 70\u0026ndash;75% onset (P3) (probability of onset occurrence in three out of four years), which could be more reliable for seedling germination than P2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, c) because it is based on meeting criteria that the cumulative rain be equal to or above the corresponding 50% weekly cumulative reference evapotranspiration in three out of four years. According to this onset strategy, Burkina Faso onset corresponded to standard weeks 20 to 23.9 in the south, 24 to 27.6 in the center, and 27.7 to 29.5 in the north, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Whereas the cessation ranged from standard week number 38\u0026ndash;40 in the north, 40\u0026ndash;41 in the center, and 41\u0026ndash;43 in the south (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Similarly, for Senegal, the 70\u0026ndash;75% onset could range from week number 24\u0026ndash;25.5 in the south, 25.6\u0026ndash;28.5 in the center, and 28.6\u0026ndash;33 in the north (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). The cessation for both Burkina Faso and Senegal is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and d. The advantage with this strategy is that replanting due to germination failure could be reduced, but the disadvantage is that it could further shorten the growing period in locations where their rainy periods are already short, like northern Burkina Faso and Senegal, which could lead to total crop loss or significant yield reduction. In addition, some late-maturing or drought-tolerant crops might require earlier planting to give high yield, which might be another disadvantages of this approach. Waongo (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) reported a dry spell of 7 days was greater in northern than in southern Burkina Faso, with a relatively higher risk of occurrence in May (\u0026gt;\u0026thinsp;20%). The risk of a dry spell\u0026thinsp;\u0026gt;\u0026thinsp;10 days in July decreases to less than 20% (Waongo \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In this study, the optimal planting time is the period when yield is maximized as simulated using the crop model. The crops gave a relatively higher yield at onset derived based on rainfall probabilities of an exceedance level of 70%. According to Sultan and Janicot (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), there was no correlation among the pre-onset dates, onset dates, and seasonal sum of rainfall for the Sahel for the climatic period 1968 to 1990, but it is more related to shifts in the ITCZ. As defined above, the LGP in this study is the difference between the onset and cessation of seasonal rainfall during the growing season. Assuming onset (P2, 50% probability), the LGP for both Burkina Faso and Senegal increases from north to south with a maximum of 170 days for Burkina Faso and 133 days for Senegal (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and b). The LGP result for Burkina Faso strongly agreed with Waongo (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The LGP for central and northern Burkina Faso ranged from 100 to 135 and 63 to 99 days, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The corresponding LGP values for central and northern Senegal were 74 to 113 days and 14 to 73 days, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). The northern most part of Senegal received a maximum of 25 rainy days of above 5 mm with a maximum LGP of 53 days, which could make it difficult to grow crops under this climate condition unless supplemented with irrigation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAssuming onset (P3, 70% probability), the LGP for Burkina Faso and Senegal ranged from 60 to 157 days and 21 to 126 days, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec, d). The shortest and longest LGP corresponded to the northern and southern parts of the countries, respectively. The LGP for northern Burkina Faso and Senegal ranged from 60 to 76 and 21 to 39 days, respectively. Based on the analysis of the growing period, northern Senegal is not suitable for rainfed agriculture, while some drought-resistant, short-maturing cultivars might be grown in northern Burkina Faso.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Evaluation of optimal planting date\u003c/h2\u003e\u003cp\u003eIn this study, we used yield as a measure of optimal planting. Yields of the major crops across the different locations were simulated based on three levels of onset probability exceedance (P1, P2, and P3) (Fig. S11a-d). Results showed that the large majority of southern Burkina Faso and Senegal gave better yields under 70% (P3) when compared to 50% (P2) or 30% (P1) onset probabilities. The optimal planting date for maize, peanuts, and millet corresponded to P3 (Fig. S11a-c). In contrast, the optimal planting date for sorghum corresponded to P1 (Fig. S11d). The 70% onset probabilities were more reliable for growing water-stress-sensitive crops such as maize, which could reduce possibilities of crop failure at germination. In addition, the LGP matches well with the growing cycle of the selected crops, although the LGP shortens under P3 compared to P2. The length of the growing season shortened from a maximum of 170 days under 50% probabilities of onset to 157 days under 70% probabilities (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and c). Based on the planting strategies, planting should start earlier in southern Burkina Faso and Senegal than the rest of each country, and planting based on P3 (70% probabilities of onset) gave higher yield. Waongo et al. (2013) reported the optimal planting date for Burkina Faso varied by location, with the earliest and latest planting for southern and northern Burkina Faso, respectively.\u003c/p\u003e\u003cp\u003eThe spatial yield levels for maize, peanuts, millet, and sorghum across Burkina Faso are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d. The yield level for the major crops follows the rainfall gradient across Burkina Faso. Yield level increased southwards, which could be due to a longer rainy period and a higher amount of rainfall in the south than in the north or central part of the country. The spatial yields for millet, peanut, and sorghum for Senegal are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea-c. Like Burkina Faso, the yield level increases with rainfall gradient across the country (yield increases from north to south). Use of optimal planting dates is less costly, which could be used as an adaptation measure for enhancing yield in Western African countries. In this study, we found that planting maize, peanuts, and millet when the 70% probability of exceedance of rainfall crosses the 50% reference evapotranspiration would be optimal. The optimal planting date was reported to be between May 1 in the southwest and July 11 in northern Burkina Faso, which varies depending on location, although planting in May is considered risky (Waongo \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The growing period can be increased by using earlier planting. The optimal planting time for the northern part is when the ITCZ reaches its northernmost position, during which rainfall is intense (crop failure is less likely at the time of germination). Accordingly, our analysis shows that rainfall played a significant role in modifying yield across the two countries. The relationship between maize yield and precipitation from planting to harvest is presented in Fig. S12a-j. There were moderately weak (R\u0026sup2; = 0.4 to 0.58) to strong (R\u0026sup2; = 0.64 to 0.75) relationships between yield and precipitation. Although rainfall played a substantial role in maize yield, the influence of the rise in temperature on yield should not be underestimated. The shortening of crop growing period could reduce accumulation of assimilates and yield (Hasanuzzaman et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Roudier et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) reported a larger yield decline because of temperature increase than rainfall changes. The rise in temperatures along with an increase in rainfall in the eastern Sahel and a decrease in rainfall in the western Sahel resulted in a decrease in agricultural production by 50 kg per capita (Defrance et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Crop yield in West Africa could decline with a median decrease of 11% and more negative (-18%) results towards the north (Sudano-Sahelian) compared to the south (Guinea) (Roudier et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Sultan and Gaetani (2016) projected yield reduction for West Africa. Agriculture in the Sudano-Sahelian zone of West Africa is expected to be impacted by climate change (Sultan and Gaetani 2016; Roudier et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). West Africa is vulnerable to climate risks because it depends on rainfed agriculture with little adaptation capacity (such as economic and institutional) (Sultan and Gaetani 2016).\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eMost of the meteorological drought occurred in Burkina Faso and Senegal before 1992. At least 15% of the past 40 years (1981\u0026ndash;2020) were meteorologically below-average rainfall years. The most severe meteorological drought occurred (in Senegal and Burkina Faso) in 1983\u0026ndash;84. During the most severe drought years, annual rainfall for most locations decreased by more than 25% of the long-term mean. The probabilities of occurrence of rainy days equal to or above 5 mm for Burkina Faso and Senegal in one out of two years and in three out of four years were not different, indicating the rainfall was stable for the majority of the years after 1990. The average number of rainy days equal to or above 5 and 10 mm ranged between 30 and 72 and 15 and 39 days, respectively, for Burkina Faso and 15 and 72 and 7 and 45 days, respectively, for Senegal. The lowest and highest number of rainy days corresponded to northern and southern locations, respectively. It is risky to grow crops under rainfed conditions in northern Burkina Faso and Senegal, where rainy days above 5 mm are limited to less than 30 days. These areas might be more suitable for growing forage grasses (animal feed or crops that do not need to harvest grains) than for grain crops. For most locations (except the north), our results showed that P3 (onset generated based on weekly cumulative rainfall probabilities approximately in three out of four years meeting 50% weekly cumulative reference evapotranspiration) is more reliable than P2 (onset generated from weekly cumulative rainfall in one out of two years meeting at least the 50% weekly cumulative reference evapotranspiration) or P1 (onset generated based on weekly cumulative rainfall probabilities in one out of three years meeting 50% weekly cumulative reference evapotranspiration).\u003c/p\u003e\u003cp\u003eHowever, it should be understood that P3 could shorten the growing period for late-maturing cultivars in locations that have short growing seasons, such as those in northern Burkina Faso and Senegal. For late-maturing cultivars, using P2 could be considered more suitable than P3 or P1. Using P3 has the advantage of reducing false starts/failures at germination or reduces replanting. However, in northern Burkina Faso and Senegal, the yield of all crops improved under P1 when compared to P2 or P3 because of the short LGP. On the other hand, sorghum yield was improved under P1 when compared to P2 or P3, attributed to its relative drought tolerance compared to other crops.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eStatements Conflict of Interest\u003c/h2\u003e\u003cp\u003eAll authors declared that no conflict or competing interest or personal relationships to influence the work in any way or form. All authors read and approved the submission of this manuscript.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eA. Araya: Conceptualization, Investigation, Methodology, Writing original draft; P.V.V. Prasad: Conceptualization, Methodology, Funding acquisition, Resources, Project administration, Visualization, Writing\u0026mdash;review \u0026amp; editing; P.K. Jha: Investigation, Formal analysis, Visualization, Writing\u0026mdash;review \u0026amp; editing; I.A. Ciampitti: Investigation, Resources, Writing\u0026mdash;review \u0026amp; editing; V. Sharda: Writing\u0026mdash;review \u0026amp; editing. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank the Feed the Future Innovation Lab for Collaborative Research on Sustainable Intensification (Grant no. AID-OAA-L-14-00006) at Kansas State University funded by the United States Agency for International Development for supporting this activity. The contents of this publication are the sole responsibility of the authors and do not reflect the views of funding agencies and representing organizations. Contribution no. 25-190-J from the Kansas Agricultural Experiment Station.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eDatasets used in this research are available upon reasonable request and time (please contact the corresponding author).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAraya A, Stroosnijder L (2011) Assessing drought risk and irrigation need in northern Ethiopia. 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Germany\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"theoretical-and-applied-climatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"taac","sideBox":"Learn more about [Theoretical and Applied Climatology](https://www.springer.com/journal/704)","snPcode":"704","submissionUrl":"https://submission.nature.com/new-submission/704/3","title":"Theoretical and Applied Climatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"climate change, onset, planting date, food security, drought, West Africa","lastPublishedDoi":"10.21203/rs.3.rs-7180722/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7180722/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study was carried out in Burkina Faso and Senegal, West Africa. The purpose of the study was to (i) characterize the climate and assess the occurrence of meteorologically below average rainfall years, (ii) evaluate the rain onset, cessation, and length of growing period, and (iii) identify the optimal planting time for maize, sorghum, pearl millet and peanut. The study showed that there is a latitudinal difference in rainfall distribution and frequency from south to north in both Burkina Faso and Senegal. Over the past 40 years period (1981\u0026ndash;2020), at least 6 years were identified as meteorologically drought years with a spatiotemporal variation in the severity. The most severe one occurred in 1983\u0026ndash;84. Occurrence of below average rainfall substantially reduced after 1990 for both Burkina Faso and Senegal. The number of rainy days with rainfall values\u0026thinsp;\u0026ge;\u0026thinsp;5 or \u0026ge;\u0026thinsp;10 mm for each growing seasons in both Burkina Faso and Senegal were highly correlated with the annual total rainfall. The lowest and highest rainfall values corresponded to northern and southern locations, respectively. Planting based on onset estimated by weekly cumulative rainfall probabilities in three out of four years meeting 50% weekly cumulative reference evapotranspiration enhanced yield and found to be suitable planting for sorghum, maize, millet and peanut in the south and central part of both countries. Yield followed the spatial rainfall and temperature gradient in both Burkina Faso and Senegal. The northern most locations were dry and thus it is not optimal to grow grain crops without irrigation.\u003c/p\u003e","manuscriptTitle":"Agroclimatic analysis for reducing planting risks in Burkina Faso and Senegal","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-11 16:10:57","doi":"10.21203/rs.3.rs-7180722/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-20T17:13:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-19T20:29:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281990997298178068006426667773359362813","date":"2025-09-28T18:36:17+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-27T17:26:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"189148456292007056471941659717927278168","date":"2025-09-27T13:45:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-28T17:11:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"221899354987840348787042207294268439661","date":"2025-08-07T20:37:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"19386841300263296274499781782776085920","date":"2025-08-06T16:05:28+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-06T15:13:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-21T22:14:23+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-21T22:14:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Theoretical and Applied Climatology","date":"2025-07-21T20:36:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"theoretical-and-applied-climatology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"taac","sideBox":"Learn more about [Theoretical and Applied Climatology](https://www.springer.com/journal/704)","snPcode":"704","submissionUrl":"https://submission.nature.com/new-submission/704/3","title":"Theoretical and Applied Climatology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"cd2f0b1f-0032-4361-a1b6-c1bc9f8da664","owner":[],"postedDate":"August 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-08T16:08:06+00:00","versionOfRecord":{"articleIdentity":"rs-7180722","link":"https://doi.org/10.1007/s00704-025-05936-8","journal":{"identity":"theoretical-and-applied-climatology","isVorOnly":false,"title":"Theoretical and Applied Climatology"},"publishedOn":"2025-12-05 15:58:28","publishedOnDateReadable":"December 5th, 2025"},"versionCreatedAt":"2025-08-11 16:10:57","video":"","vorDoi":"10.1007/s00704-025-05936-8","vorDoiUrl":"https://doi.org/10.1007/s00704-025-05936-8","workflowStages":[]},"version":"v1","identity":"rs-7180722","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7180722","identity":"rs-7180722","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}