Patterns of Rainfall and Temperature and their Relationships with Potential Evapotranspiration rates over recent years (1981-2022) in Southwestern Uganda, East Africa.

Abstract Uganda in East Africa is experiencing highly variable rainfall that is exacerbated by temperatures warming at faster rates. This study analyzed rainfall and temperature patterns in comparison with the potential evaporation transpiration rates (PET) for southwestern Uganda for varying period from 1981-2022. For rainfall onset date (OD), threshold of 0.85 mm for a rainy day, rainfall of 20 mm accumulated over 5 days with at least 3 rain days and dry spell not exceeding 9 days in the next 30 days were used. The rainfall cessation dates (RCDs) is determined when Water Balance (WB) falls below 5 mm in 7 days in the last month of the expected season (May and December) for the first and second season respectively. Standardized rainfall anomaly was utilized to show seasonal and annual rainfall variability. Pearson’s correlation (r) coefficient was used to show the relationship between weather variables (rainfall, temperature) and PET at five rainfall stations. Results showed highly varied onset and cessation dates for March-May (MAM) seasonal rainfall compared to those of September-December (SOND). Results further revealed statistically significantly increasing trends in both maximum and minimum temperatures across the region, with the highest rate of increase of maximum temperature of 0.70oC and 0.65oC for minimum temperature per decade respectively. Moreover, the maximum temperature and PET showed strong positive correlation coefficient (r) that ranged from 0.82 to 0.90 across the regions, which likely contributes to excess evaporation from the surfaces, soil moisture deficits that negatively affect plants biomass production, low crop yields and food insecurity. We recommend water management and conservation practices such as mulching, zero tillage, planting drought-resistant crops, and using affordable irrigation systems during period of water deficit.