Impact of Submarine Groundwater Discharge, Climate Change, and Land Use on Korea’s Coast

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This study provides the first regional estimates of fresh SGD along the entire coast of the Korean Peninsula from 1980 to 2016, utilizing established water balance methods. Our results indicate that the western and southern coasts of South Korea experience higher fresh SGD rates due to greater net precipitation compared to the North Korean region. The impact of drainage length is evident when examining the East and West coasts. Notably, substantial tidal flats on the West coast, where tidal differences significantly influence high SGD rates, are particularly significant. Climate change affects fresh SGD variation, with South Korea's western and southern coasts showing rising trends in spring and winter, while North Korean coastal watersheds display a consistent increase across all seasons. Our findings highlight the vulnerability of Korean coastal regions to climate change and land use development, affecting 15% of the coastline. Specifically, the increased development and agricultural land in South Korean coastal catchments have exacerbated vulnerability by 38% since 1990, driven by economic growth, population expansion, and shifts in cultivated crops. Earth and environmental sciences/Hydrology Earth and environmental sciences/Climate sciences/Hydrology Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Submarine groundwater discharge (SGD) represents the subsurface flow of water entering the ocean 1,2 . SGD impacts the coastal environment in various ways, depending on factors such as discharge scale, groundwater quality, and human proximity to the discharge zone 3 . On the Korean Peninsula, groundwater extraction for agricultural, industrial, and domestic purposes is increasing, potentially impacting the SGD process in coastal aquifers 4,5,6 . Quantifying SGD estimates and examining their spatiotemporal variability are crucial. At a local scale, common field techniques for assessing of fresh SGD include seepage meters 7,8,9 , piezometers 10 , and the use of natural tracers such as radium and radon 11,12,13 . However, direct measurements are limited by spatial coverage constraints, posing significant challenges in quantifying fresh SGD due to its high heterogeneity. Computational methods provide a valuable tool for predicting fresh SGD at various spatial scales, from global (e.g., ref. 14,15) to regional perspectives (e.g., ref. 16,17,18). South Korea has been actively involved in calculating both local and regional SGD estimates, utilizing both direct seepage measurements and indirect isotopic methods 6,13,19,20,21 . However, there has been no attempt to estimate fresh SGD along the entire Korean Peninsula coast using the water balance approach in combination with advanced land surface models. Previous studies have applied land surface models to estimate SGD using the Global Land Data Assimilation System (GLDAS) to calculate water budgets for coastal aquifers and approximate net recharge rates on a coarse resolution 14,15,18 . Despite the improvements, GLDAS still struggles to capture the complex topography of coastal regions due to spatial limitations when applied to the Korean Peninsula. Previous assessments of fresh SGD have primarily focused on long-term averages, failing to provide the temporal evolution of fresh SGD rates or assess the impact of climate change on SGD variations across coastal catchments 14,15 . Recently, the Korea Land Data Assimilation System (KLDAS) has been developed within the NASA Land Information System framework 22 , benefiting from the incorporation of local precipitation forcing datasets and soil texture maps 23,24 . The KLDAS supports an effective hydrological monitoring system, providing continuous regional high-resolution water balance variables across the Korean Peninsula. In this study, we undertake a comprehensive analysis focusing on four key aspects. Firstly, we quantify fresh SGD rates along the entire coast of the Korean Peninsula using a water balance approach through KLDAS for the period 1980-2016. We investigate the spatial pattern of average fresh SGD rates, considering factors such as net precipitation and coastal drainage length across regions. Secondly, we assess the influence of climate change on fresh SGD rate variations over a 37-year model period. We analyze annual and seasonal trends using the Mann-Kendall trend test. Finally, we examine the susceptibility of coastal areas in South Korea to offshore contamination and saltwater intrusion, accounting for land use development over decades. Regional analysis of fresh SGD rates Korea comprises numerous small-sized islands, primarily located in the West Sea and South Sea, accounting for a significant portion at 43.6% of the total. Despite their substantial count, the SGD from these minor islands remains relatively small across all regions due to their limited drainage lengths (Extended Data Fig. 1). We exclude these minor islands to prevent potential statistical biases (Fig. 1). The topography of the Korean Peninsula significantly influences its annual rainfall patterns. The southwestern region, positioned on the windward side of high mountains, receives abundant rainfall, while the northeastern region, surrounded by mountains, experiences lower precipitation levels (Extended Data Fig. 1b). The drainage length, representing the average distance from any location in the coastal catchment to the shoreline, tends to be smaller in the southwestern region with small-sized islands (Extended Data Fig. 1c). Various land surface models were employed to calculate water budgets for coastal aquifers and estimate fresh SGD along the Korean Peninsula (Extended Data Table 1). The ensemble average for the entire domain was determined to be 279 m 2 /year, with the uncertainty in fresh SGD estimated at 16.3 m 2 /year. The patterns of fresh SGD are influenced by a combination of drainage geometry and climate conditions (Fig 2). In the North Korean region, including areas like Pyongan, Hwangnam, and Hamgyong, both net precipitation and fresh SGD exhibit lower values. Conversely, the western and southern coasts of South Korea experience higher levels of net precipitation and fresh SGD. The impact of drainage length becomes apparent when examining the East and West coasts. For instance, net precipitation levels are similar in the Chungman and Gangwon regions, but fresh SGD rates are approximately 47% greater in the Chungman region. This disparity can be attributed to the presence of extensive coastal drainage systems within complex terrains. Substantial tidal flats are present along the West coast, where tidal differences play a crucial role in influencing high SGD rates 5 . Additionally, the West coast is predominantly composed of sandy tidal flats, which can increase fresh SGD rates. The nutrient runoff via groundwater on large continental shelves affects potential ecological systems and needs continuous monitoring. Jeju Island exhibits notably high levels of SGD. Groundwater on the island originates from volcanic rock aquifers, primarily consisting of permeable basalts. The island's significant elevation changes and permeable volcanic bedrock, coupled with its limited river drainage infrastructure, contribute to the elevated rates of SGD. This aspect is particularly relevant as groundwater contamination plays a pivotal role in influencing coastal ecosystems and contributing to eutrophication. Impact of climate change on the fresh SGD rates SGD exhibits a rising trend across the entirety of the Korean Peninsula (Fig. 3a). This pattern aligns with the observed trend in net precipitation (Fig. 3b). Most regions in South Korea do not display statistically significant trends, either increasing or decreasing. However, discernible statistically significant trends are evident in the Incheon-Gyeonggi region and various areas within North Korea. Seasonal patterns in fresh SGD rates (Figs. 4a-4d) closely mirror the precipitation dynamics, exhibiting concentration predominantly during the summer months. Positioned within the temperate monsoon climate zone, the Korean Peninsula distinctly experiences the seasons of spring, summer, autumn, and winter. Spring and autumn are marked by clear and dry weather influenced by migratory high-pressure systems, while summer sees hot and humid conditions due to the impact of the North Pacific high-pressure system. Conversely, winter is characterized by cold and dry conditions influenced by the continental high-pressure system. Notably, during the summer season, rainfall constitutes 54% of the annual precipitation. This discernible trend is most conspicuous in the watersheds along the western and southern coasts of the Korean Peninsula during the summer (Fig. 4b). Conversely, watersheds along the eastern coast consistently exhibit low SGD rates throughout all seasons. The primary contributing factor to this phenomenon is the higher relative rainfall observed on the western and southern coasts compared to the eastern coast. Furthermore, the intricate coastline features in the western and southern seas, characterized by longer drainage lengths, make fresh SGD rates highly responsive to variations in precipitation. Examining the seasonal trends of fresh SGD rates (Figs. 4e-4h), notable distinctions between South and North Korea become apparent. Coastal watersheds in North Korea show a consistent trend of increasing fresh SGD rates across all seasons. In contrast, regions of South Korea, including the western and southern coasts and Jeju Island, distinctly exhibit rising trends in fresh SGD during both the spring (Fig. 4e) and winter (Fig. 4h), while trends observed during the summer (Fig. 4f) and fall (Fig. 4g) are subdued. The spring season is influenced by climate change, resulting in heightened rainfall in these areas. Additionally, reduced soil moisture freezing due to rising temperatures during winter leads to increased surface and subsurface water inflow. Impact of decadal land use changes on coastal vulnerability Fresh SGD estimates also reveal potential contamination threats to the ocean and fisheries, upon which coastal populations heavily rely (Fig. 5a). Our definition of vulnerability generally holds true when increases in onshore aquifer contaminant concentrations coincide with a higher fraction of developed land and when the coastal supply rate correlates with elevated fresh SGD rates. Coastal areas with above-average fresh SGD and land development are particularly vulnerable to groundwater-borne contamination, accounting for 15% of the entire coastline (Fig 5a). Vulnerable regions include the western and southern parts of the Korean Peninsula. Notably, almost all of the coastal catchments in the Jeju Island area are susceptible to contamination. According to the Land Cover Change Map between 1980 and 2010 from the Ministry of Environment of South Korea (https://egis.me.go.kr), developed and agricultural lands increased by 2% and 24%, respectively, in the Jeju Island area, which is situated along the coastline. This developmental expansion contributes to elevated nutrient loads in the groundwater. Given that Jeju Island is a volcanic island and heavily relies on groundwater for its water resources, and considering that a majority of its population resides along the coast, addressing this issue is crucial. The reliance of drinking water, agriculture, and industrial activities on freshwater derived from underground sources and surface runoff underscores the need for continuous monitoring of nutrient inputs from fresh SGD 21 . Fig. 5a also illustrates the vulnerability of coastal aquifers to saltwater intrusion. Saltwater intrusion can occur in areas where groundwater is discharged into the ocean through underground conduits as part of SGD. Vulnerability to saltwater intrusion is particularly high in the southwest regions (i.e., Jeolla and Gyeongnam) (Fig. 5a). Coastal aquifers in these areas cannot be directly used for agriculture, such as cultivating salt-sensitive crops. These regions are especially susceptible to excessive groundwater extraction and salinity damage during droughts caused by climate change. According to the 2022 Marine Infiltration Survey Report, compiled by the Korea Rural Community Corporation (https://www.groundwater.or.kr), a total of 225 in-situ gauges in South Korea show that 31% of gauges continuously decrease the level of coastal aquifers, and 38% of gauges continuously increase electrical conductivity. Furthermore, ongoing global warming trends contribute to a consistent rise in sea levels, which poses additional challenges to coastal lowland agricultural areas, such as an increasing risk of flooding and saltwater intrusion. The Korea Hydrographic and Oceanographic Agency (www.khoa.go.kr) conducted an analysis of sea level height data gathered from 21 coastal tide gauging stations. The findings also indicate that over the past 34 years (1989 to 2022), the sea level along the Korean coast has experienced a rise at a rate of 3.03 mm/year, culminating in a total average increase of approximately 10.3 cm. In Jeju Island, both the western and eastern regions are vulnerable to offshore contamination and saltwater intrusion. As mentioned earlier, these areas rely primarily on groundwater to meet their resource demands. If groundwater extraction reduces fresh SGD below a critical threshold, salinization can occur 25 . Fig. 5b illustrates the changes in developed and agricultural land in South Korean coastal catchments since 1990 and their corresponding impact on vulnerability to offshore contamination. Note that the North Korea region was excluded from the study due to limited access to datasets. The overall proportion of developed and agricultural land has consistently increased from 1990 to 2020. Specifically, the developed area has continuously expanded, while agricultural land has steadily decreased. These changes have exacerbated the vulnerability of offshore contamination-prone regions by 38% since 1990 with the issue notably concentrated in the western and southern coastal regions. The analysis of GRACE TWS anomalies 26 also reveals a decreasing pattern of groundwater across coastal catchments. Extended Data Fig. 2 depicts Fig. S2 depicts the anomalies in TWS (mm) over coastal catchments from GRACE during 2002–2016, along with their piecewise linear trends. TWS represents an integrated measure of the terrestrial water budget, encompassing groundwater, soil moisture, surface water, ice, snow, and water in vegetation. While TWS does not directly measure groundwater storage, changes in groundwater storage trends can be identified through TWS fluctuations. Coastal catchments do not contain streams, and TWS is more similar to groundwater storage compared to non-coastal catchments. The figure indicates no significant change until 2011, but from 2011 to 2016, a notable depletion of TWS (-0.79 mm/month) is evident. This issue primarily arises as domestic agriculture shifts towards high-value facility farming, leading to increased groundwater usage in these coastal areas. Implications for expanding the perspective The outcomes of this research provide a fundamental foundation and support for a nationwide coastal vulnerability monitoring system. Our regional LSMs enable the continuous assessment of regional recharge rates and provide land-derived SGD rates along the coast of the Korean Peninsula. To enhance the accuracy of SGD rates using LSM approaches, it is essential to integrate local meteorological forcing datasets and land surface parameters into our regional LSM. This integration will help derive hydrologic variables relevant to SGD and allow for more precise topography for improved delineation of coastal catchments. Additionally, incorporating groundwater flow models on a local scale is necessary to explicitly address lateral groundwater flow. Our LSM-based SGD estimations should be integrated into the existing groundwater measurement network. The Groundwater Information Management and Service Center (https://www.gims.go.kr) must carefully consider various SGD management factors. In addition to field measurements, satellite observational data and remote sensing techniques can complement proactive coastal vulnerability monitoring alongside the LSM 27 . GRACE data are valuable for providing groundwater storage anomalies across coastal catchments. The thermal infrared sensors of optical satellite missions can resolve the spatial variation of SGD rates and detect potential groundwater discharge areas along the coast of the Korean Peninsula. Methods Estimation of fresh SGD Coastal catchments for fresh SGD were identified by manipulating the HydroSHED 15-arc second product ( https://www.hydrosheds.org/ ). Note that the selected coastal catchments are designed to exclude streams by construction. Instead, they are situated between established stream-coast intersections. The coastlines were delineated through the extraction of polyline products utilizing feature type attributes. We derive the adjusted net recharge rate by averaging the infiltrating runoff from three LSMs: Noah v3.9 32,33 , Noah-MP v4.0.1 34,35 , and JULES v5.5 36,37 . The three LSMs encompass a blend of models featuring notable variations in parameterizations and model physics 38 . The LSMs were run using a 15-minute timestep over a 37-year period (1980–2016) at a spatial resolution of 1 km. The initial conditions for the simulation were established by running the LSMs from 1980 to 2016 twice, followed by a reinitialization in 1980. KLDAS was used as a driving force for the LSMs. The KLDAS encompasses the entirety of the Korean Peninsula, spanning from 33 to 44 degree north and 124 to 132 degree east. The KLDAS operates at a 1-km spatial resolution, incorporating local precipitation forcing datasets and soil texture maps. The recharge rate ( r ) for each grid cell was calculated as the average of daily infiltrating runoff, taking into account land cover types and including coastal catchments within the LSMs. The annual recharge volume for each coastal catchment was calculated by multiplying the catchment area ( A ) by the annual recharge closest to the catchment centroid. Finally, to derive the fresh SGD flux (m²/year), the annual recharge volume was divided by the corresponding coastline length ( L ). SGD (m 2 /year) = r (m/year) × A (m 2 ) / L (m) ( 1 ) We simplify our calculations by excluding groundwater contributions from upland catchments to coastal catchments, which may lead under-estimated fresh SGD. Additionally, human activities such as groundwater pumping (e.g., for irrigation and urban water supply) are neglected, which can lead to high estimation. Mann-Kendal trend test The Mann-Kendall test, a non-parametric technique applied to evaluate monotonic trends in environmental datasets such as climate or hydrological data 39 , employs the S statistic to determine the existence and extent of upward or downward patterns observed over time: $$S={\sum }_{k=1}^{n-1}{\sum }_{j=k+1}^{n}sign({x}_{j}-{x}_{k})$$ 2 where x represents the time series variable, with subscripts j and k denoting observation times. The \(sign({x}_{j}-{x}_{k})\) function yields values of + 1, 0, or -1, indicating increasing, no, and decreasing trends, respectively. The S values are scaled to a range of [-1, 1] for improved interpretability. The null hypothesis posits that there is no statistically significant trend in the data, with significance set at a level of 5% (or 95% confidence level). Estimation of coastal vulnerability to offshore contamination Following the ref. 14, we classified coastlines as susceptible to groundwater contamination when the proportion of developed and agricultural land surpassed the average (38.7%) and the fresh SGD flux exceeded the average (279 m 2 /year). Our vulnerability criteria generally apply if onshore aquifer contaminant concentrations increase alongside the fraction of developed land, and if coastal supply rates rise with fresh SGD rates, although multiple factors can influence contaminant flux to the coast. To determine the percentage of developed and agricultural land in South Korean coastal catchments, we utilized the 2010 Land Cover Map from the Ministry of Environment of South Korea (https://egis.me.go.kr), which categorizes land into seven major types at a 30-meter resolution. For North Korea, we extracted land fraction data using the Moderate Resolution Imaging Spectroradiometer (MODIS) Land Cover Type (MCD12Q1) V6.1 2010 dataset 36 . The MODIS MCD12Q1 provides annual global land cover maps at a 500-meter resolution from 2001 to the present. We converted the raster data to a polygon shapefile and calculated the total areas of developed and crop land within each catchment. Estimation of coastal vulnerability to saltwater intrusion To assess vulnerability to saltwater intrusion in South Korea, with the exception of Jeju, we utilized data from the 2010 Marine Infiltration Survey Report, compiled by the Korea Rural Community Corporation ( https://www.groundwater.or.kr ). This report relied on data collected from 107 in-situ gauges and categorized vulnerability into four stages (interest, attention, caution, and serious) based on parameters such as electrical conductivity, its variations, and changes in reservoir levels. Similarly, for the Jeju Island region, we sourced information from the 2022 Groundwater Monitoring Report, prepared by the Jeju Groundwater Research Center (https://water.jeju.go.kr). Note that we did not assess the vulnerability to saltwater intrusion in North Korea due to limited available data, and the in-situ gauges do not cover all coastal catchments in South Korea. Impact of decadal land use changes on coastal vulnerability to offshore contamination To evaluate the proportion of developed and agricultural land in South Korean coastal catchments over time, we analyzed four sequential datasets (1990, 2000, 2010, and 2020) from the Land Cover Map (Fig. 5b). This methodology mirrors the approach used for assessing offshore contamination vulnerability. We established specific thresholds for averaged fresh SGD flux corresponding to the year of SGD estimation. However, due to the study's timeframe, the 2020 data was beyond our scope. To address this, we utilized the 2012 SGD estimates as a proxy for the 2020 estimates, given the similarity in precipitation patterns and spatial distribution between 2012 and 2020. TWS anomalies over the coastal catchment We utilize three distinct GRACE products, which are provided monthly on 1° horizontal resolution grids by the University of Texas Center for Space Research, Jet Propulsion Laboratory, and German Research Centre for Geosciences. These products are derived from the RL06v04 spherical harmonics fields 37 . To extract TWS anomalies over the coastal catchments, we interpolated the GRACE datasets to fit the 1-km LSM grid and extracted the value closest to the catchment centroid. Declarations Data availability HydroSHED 15-arc second products were downloaded from the HydroSHED website (https://www.hydrosheds.org/). KLDAS datasets can be obtained by requesting them from the authors. The land cover map for South Korea was downloaded from the Ministry of Environment of South Korea (https://egis.me.go.kr). The MODIS MCD12Q1 V6.1 was obtained from the Land Processes Distributed Active Archive Center (https://lpdaac.usgs.gov/products/mcd12q1v061/). Gauge datasets for saltwater intrusion in South Korea are available from the Korea Rural Community Corporation (https://www.groundwater.or.kr). Saltwater intrusion observations for Jeju can be found at the Jeju Groundwater Research Center (https://water.jeju.go.kr). GRACE datasets were downloaded from NASA JPL GRACE Tellus (https://grace.jpl.nasa.gov). Code availability The three LSMs (Noah v3.9, Noah-MP v4.0.1, and JULES v5.5) are available via the NASA Land Information System (https://github.com/NASA-LIS/LISF). 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Supplementary Files Extendeddata.docx Cite Share Download PDF Status: Published Journal Publication published 14 Feb, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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-4558926","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":317462312,"identity":"0603a74d-7b32-4459-8048-082b30b1fee6","order_by":0,"name":"Yeosang Yoon","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYNCDDyTrYJxBshZmHmJUGRxvPvzh545aEOPYY9sddvb8DewXH+PTa3DmWJpk75njIEa6ce6Z5MQZB3iKjfFquZFjxsDbdgzMkM5tY05gOMCTJonPUwb33xh//AvTYtlWby9PUMsNHgNp3rYaiBbGtsOMGw6wH5PAF9qSZ9LSpGXbDvBIgj3Vdjxx42EeZgN8WviOHz788W1bnRwfMMQkfrZV28sdb3/4IAGPFoUDYOowD5TBAIodAzwaGBjkG8BUHYwBAuwP8GoZBaNgFIyCEQcAkxhRKgpaJuMAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-3095-1136","institution":"NASA Goddard Space Flight Center","correspondingAuthor":true,"prefix":"","firstName":"Yeosang","middleName":"","lastName":"Yoon","suffix":""},{"id":317462313,"identity":"bfe61df4-83df-48e1-93f0-267db28d787c","order_by":1,"name":"Hahn Chul Jung","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Hahn","middleName":"Chul","lastName":"Jung","suffix":""}],"badges":[],"createdAt":"2024-06-10 15:20:53","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4558926/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4558926/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-02084-9","type":"published","date":"2025-02-14T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":60876250,"identity":"4bf9e5ba-a737-4c5f-b7f5-a5c9ecf5c6ca","added_by":"auto","created_at":"2024-07-23 06:04:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":408419,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMap of fresh SGD rates along the coastline of the Korean Peninsula.\u003c/strong\u003e The average fresh SGD rate (m\u003csup\u003e2\u003c/sup\u003e/year) is calculated by multiplying the average annual net recharge, obtained from three land surface models, by the drainage length. Note that, minor islands, mainly located in the West Sea and South Sea, were excluded to prevent potential statistical biases. The sub-regions with the shaded relief map are shown as the background. As an example, three expanded views display coastal recharge zones colored according to the rate of fresh SGD.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/ea138bd3b96a75d07ca11e7b.png"},{"id":60876254,"identity":"12b97d6d-28a4-4219-b013-18472278e070","added_by":"auto","created_at":"2024-07-23 06:04:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":122978,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpatial analysis of the average rates of fresh SGD, net precipitation, and coastal drainage length across regions.\u003c/strong\u003e The color gradient corresponds to the fresh SGD values. Net precipitation is represented by the bar height, utilizing a radial axis spanning from 0 to 1200 kg/m\u003csup\u003e2\u003c/sup\u003e. The dot height conveys the coastal drainage length with a radial axis ranging from 0 to 1.2 km.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/9413f6d52e9b8d5bcd0e16f8.png"},{"id":60876749,"identity":"8380b7f8-347d-4edd-9a18-db32a5554f92","added_by":"auto","created_at":"2024-07-23 06:12:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":262021,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTrend analyses of fresh SGD and net precipitation rates usingthe Mann-Kendall trend test\u003c/strong\u003e. Maps illustrating the Mann-Kendall S-statistics for (a) SGD and (b) net precipitation (Net P) were generated across coastal catchments. (c) Time series analyses were performed to calculate the domain-averaged mean annual SGD and Net P for the years 1980-2016.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/3cc1f3519aeaaec7a6f6bbce.png"},{"id":60876252,"identity":"68890cfe-29c3-47ca-8372-e98f1b3a636c","added_by":"auto","created_at":"2024-07-23 06:04:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":368620,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSeasonal analyses of fresh SGD rates for the years 1980-2016\u003c/strong\u003e. Maps for fresh SGD rates in (a) spring, (b) summer, (c) fall, and (d) winter. Concurrently, Mann-Kendall S-statistic estimates for (e) spring, (f) summer, (g) fall, and (h) winter were calculated to assess trends in the seasonal variations of fresh SGD rates.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/c6045b2715ef271c127ddbe2.png"},{"id":60876748,"identity":"071643a1-62f7-4c96-9b7a-fd6efbb90ab7","added_by":"auto","created_at":"2024-07-23 06:12:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":156552,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAssessment of coastal vulnerability of the Korean Peninsula.\u003c/strong\u003e (a) Map of coastal vulnerability to offshore contamination and saltwater intrusion. Areas vulnerable to offshore contamination (indicated in dark blue) are identified where the rate of fresh SGD surpasses the average and the usage of developed or agricultural land exceeds the average. Vulnerability to saltwater intrusion (highlighted in orange) is identified in regions where low fresh SGD or high groundwater extraction may lead to complete saltwater invasion. Vulnerability to saltwater intrusion in North Korea was not assessed due to limited available data. Coastal areas indicated in light blue are susceptible to both offshore contamination and saltwater intrusion. (b) The impact of decadal land use changes in South Korean coastal catchments on vulnerability to offshore contamination is explored.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/b08e5d5f539918830465b2a6.png"},{"id":76345259,"identity":"b0e2938a-1d10-46b7-9f5f-2e3498d23b0e","added_by":"auto","created_at":"2025-02-15 08:05:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2083531,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/59913c1b-61e9-4ac4-9d49-d3030bf93087.pdf"},{"id":60876255,"identity":"42ece095-1996-4756-bb5f-afcaa1a6875c","added_by":"auto","created_at":"2024-07-23 06:04:34","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1214451,"visible":true,"origin":"","legend":"","description":"","filename":"Extendeddata.docx","url":"https://assets-eu.researchsquare.com/files/rs-4558926/v1/d652bbc4853022160bacc53a.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Impact of Submarine Groundwater Discharge, Climate Change, and Land Use on Korea’s Coast","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSubmarine groundwater discharge (SGD) represents the subsurface flow of water entering the ocean\u003csup\u003e1,2\u003c/sup\u003e. SGD impacts the coastal environment in various ways, depending on factors such as discharge scale, groundwater quality, and human proximity to the discharge zone\u003csup\u003e3\u003c/sup\u003e. On the Korean Peninsula, groundwater extraction for agricultural, industrial, and domestic purposes is increasing, potentially impacting the SGD process in coastal aquifers\u003csup\u003e4,5,6\u003c/sup\u003e. Quantifying SGD estimates and examining their spatiotemporal variability are crucial. At a local scale, common field techniques for assessing of fresh SGD include seepage meters\u003csup\u003e7,8,9\u003c/sup\u003e, piezometers\u003csup\u003e10\u003c/sup\u003e, and the use of natural tracers such as radium and radon\u003csup\u003e11,12,13\u003c/sup\u003e. However, direct measurements are limited by spatial coverage constraints, posing significant challenges in quantifying fresh SGD due to its high heterogeneity.\u003c/p\u003e\n\u003cp\u003eComputational methods provide a valuable tool for predicting fresh SGD at various spatial scales, from global (e.g., ref. 14,15) to regional perspectives (e.g., ref. 16,17,18). South Korea has been actively involved in calculating both local and regional SGD estimates, utilizing both direct seepage measurements and indirect isotopic methods\u003csup\u003e6,13,19,20,21\u003c/sup\u003e. However, there has been no attempt to estimate fresh SGD along the entire Korean Peninsula coast using the water balance approach in combination with advanced land surface models. Previous studies have applied land surface models to estimate SGD using the Global Land Data Assimilation System (GLDAS) to calculate water budgets for coastal aquifers and approximate net recharge rates on a coarse resolution\u003csup\u003e14,15,18\u003c/sup\u003e. Despite the improvements, GLDAS still struggles to capture the complex topography of coastal regions due to spatial limitations when applied to the Korean Peninsula. Previous assessments of fresh SGD have primarily focused on long-term averages, failing to provide the temporal evolution of fresh SGD rates or assess the impact of climate change on SGD variations across coastal catchments\u003csup\u003e14,15\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eRecently, the Korea Land Data Assimilation System (KLDAS) has been developed within the NASA Land Information System framework\u003csup\u003e22\u003c/sup\u003e, benefiting from the incorporation of local precipitation forcing datasets and soil texture maps\u003csup\u003e23,24\u003c/sup\u003e. The KLDAS supports an effective hydrological monitoring system, providing continuous regional high-resolution water balance variables across the Korean Peninsula. In this study, we undertake a comprehensive analysis focusing on four key aspects. Firstly, we quantify fresh SGD rates along the entire coast of the Korean Peninsula using a water balance approach through KLDAS for the period 1980-2016. We investigate the spatial pattern of average fresh SGD rates, considering factors such as net precipitation and coastal drainage length across regions. Secondly, we assess the influence of climate change on fresh SGD rate variations over a 37-year model period. We analyze annual and seasonal trends using the Mann-Kendall trend test. Finally, we examine the susceptibility of coastal areas in South Korea to offshore contamination and saltwater intrusion, accounting for land use development over decades.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRegional analysis of fresh SGD rates\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eKorea comprises numerous small-sized islands, primarily located in the West Sea and South Sea, accounting for a significant portion at 43.6% of the total. Despite their substantial count, the SGD from these minor islands remains relatively small across all regions due to their limited drainage lengths (Extended Data Fig. 1). We exclude these minor islands to prevent potential statistical biases (Fig. 1). The topography of the Korean Peninsula significantly influences its annual rainfall patterns. The southwestern region, positioned on the windward side of high mountains, receives abundant rainfall, while the northeastern region, surrounded by mountains, experiences lower precipitation levels (Extended Data Fig. 1b). The drainage length, representing the average distance from any location in the coastal catchment to the shoreline, tends to be smaller in the southwestern region with small-sized islands (Extended Data Fig. 1c). Various land surface models were employed to calculate water budgets for coastal aquifers and estimate fresh SGD along the Korean Peninsula (Extended Data Table 1). The ensemble average for the entire domain was determined to be 279 m\u003csup\u003e2\u003c/sup\u003e/year, with the uncertainty in fresh SGD estimated at 16.3 m\u003csup\u003e2\u003c/sup\u003e/year.\u003c/p\u003e\n\u003cp\u003eThe patterns of fresh SGD are influenced by a combination of drainage geometry and climate conditions (Fig 2). In the North Korean region, including areas like Pyongan, Hwangnam, and Hamgyong, both net precipitation and fresh SGD exhibit lower values. Conversely, the western and southern coasts of South Korea experience higher levels of net precipitation and fresh SGD. The impact of drainage length becomes apparent when examining the East and West coasts. For instance, net precipitation levels are similar in the Chungman and Gangwon regions, but fresh SGD rates are approximately 47% greater in the Chungman region. This disparity can be attributed to the presence of extensive coastal drainage systems within complex terrains. Substantial tidal flats are present along the West coast, where tidal differences play a crucial role in influencing high SGD rates\u003csup\u003e5\u003c/sup\u003e. Additionally, the West coast is predominantly composed of sandy tidal flats, which can increase fresh SGD rates. The nutrient runoff via groundwater on large continental shelves affects potential ecological systems and needs continuous monitoring. Jeju Island exhibits notably high levels of SGD. Groundwater on the island originates from volcanic rock aquifers, primarily consisting of permeable basalts. The island\u0026apos;s significant elevation changes and permeable volcanic bedrock, coupled with its limited river drainage infrastructure, contribute to the elevated rates of SGD. This aspect is particularly relevant as groundwater contamination plays a pivotal role in influencing coastal ecosystems and contributing to eutrophication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImpact of climate change on the fresh SGD rates\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSGD exhibits a rising trend across the entirety of the Korean Peninsula (Fig. 3a). This pattern aligns with the observed trend in net precipitation (Fig. 3b). Most regions in South Korea do not display statistically significant trends, either increasing or decreasing. However, discernible statistically significant trends are evident in the Incheon-Gyeonggi region and various areas within North Korea.\u003c/p\u003e\n\u003cp\u003eSeasonal patterns in fresh SGD rates (Figs. 4a-4d) closely mirror the precipitation dynamics, exhibiting concentration predominantly during the summer months. Positioned within the temperate monsoon climate zone, the Korean Peninsula distinctly experiences the seasons of spring, summer, autumn, and winter. Spring and autumn are marked by clear and dry weather influenced by migratory high-pressure systems, while summer sees hot and humid conditions due to the impact of the North Pacific high-pressure system. Conversely, winter is characterized by cold and dry conditions influenced by the continental high-pressure system. Notably, during the summer season, rainfall constitutes 54% of the annual precipitation. This discernible trend is most conspicuous in the watersheds along the western and southern coasts of the Korean Peninsula during the summer (Fig. 4b). Conversely, watersheds along the eastern coast consistently exhibit low SGD rates throughout all seasons. The primary contributing factor to this phenomenon is the higher relative rainfall observed on the western and southern coasts compared to the eastern coast. Furthermore, the intricate coastline features in the western and southern seas, characterized by longer drainage lengths, make fresh SGD rates highly responsive to variations in precipitation. Examining the seasonal trends of fresh SGD rates (Figs. 4e-4h), notable distinctions between South and North Korea become apparent. Coastal watersheds in North Korea show a consistent trend of increasing fresh SGD rates across all seasons. In contrast, regions of South Korea, including the western and southern coasts and Jeju Island, distinctly exhibit rising trends in fresh SGD during both the spring (Fig. 4e) and winter (Fig. 4h), while trends observed during the summer (Fig. 4f) and fall (Fig. 4g) are subdued. The spring season is influenced by climate change, resulting in heightened rainfall in these areas. Additionally, reduced soil moisture freezing due to rising temperatures during winter leads to increased surface and subsurface water inflow.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImpact of decadal land use changes on coastal vulnerability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFresh SGD estimates also reveal potential contamination threats to the ocean and fisheries, upon which coastal populations heavily rely (Fig. 5a). Our definition of vulnerability generally holds true when increases in onshore aquifer contaminant concentrations coincide with a higher fraction of developed land and when the coastal supply rate correlates with elevated fresh SGD rates. Coastal areas with above-average fresh SGD and land development are particularly vulnerable to groundwater-borne contamination, accounting for 15% of the entire coastline (Fig 5a). Vulnerable regions include the western and southern parts of the Korean Peninsula. Notably, almost all of the coastal catchments in the Jeju Island area are susceptible to contamination. According to the Land Cover Change Map between 1980 and 2010 from the Ministry of Environment of South Korea (https://egis.me.go.kr), developed and agricultural lands increased by 2% and 24%, respectively, in the Jeju Island area, which is situated along the coastline. This developmental expansion contributes to elevated nutrient loads in the groundwater. Given that Jeju Island is a volcanic island and heavily relies on groundwater for its water resources, and considering that a majority of its population resides along the coast, addressing this issue is crucial. The reliance of drinking water, agriculture, and industrial activities on freshwater derived from underground sources and surface runoff underscores the need for continuous monitoring of nutrient inputs from fresh SGD\u003csup\u003e21\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFig. 5a also illustrates the vulnerability of coastal aquifers to saltwater intrusion. Saltwater intrusion can occur in areas where groundwater is discharged into the ocean through underground conduits as part of SGD. Vulnerability to saltwater intrusion is particularly high in the southwest regions (i.e., Jeolla and Gyeongnam) (Fig. 5a). Coastal aquifers in these areas cannot be directly used for agriculture, such as cultivating salt-sensitive crops. These regions are especially susceptible to excessive groundwater extraction and salinity damage during droughts caused by climate change. According to the 2022 Marine Infiltration Survey Report, compiled by the Korea Rural Community Corporation (https://www.groundwater.or.kr), a total of 225 in-situ gauges in South Korea show that 31% of gauges continuously decrease the level of coastal aquifers, and 38% of gauges continuously increase electrical conductivity. Furthermore, ongoing global warming trends contribute to a consistent rise in sea levels, which poses additional challenges to coastal lowland agricultural areas, such as an increasing risk of flooding and saltwater intrusion. The Korea Hydrographic and Oceanographic Agency (www.khoa.go.kr) conducted an analysis of sea level height data gathered from 21 coastal tide gauging stations. The findings also indicate that over the past 34 years (1989 to 2022), the sea level along the Korean coast has experienced a rise at a rate of 3.03 mm/year, culminating in a total average increase of approximately 10.3 cm. In Jeju Island, both the western and eastern regions are vulnerable to offshore contamination and saltwater intrusion. As mentioned earlier, these areas rely primarily on groundwater to meet their resource demands. If groundwater extraction reduces fresh SGD below a critical threshold, salinization can occur\u003csup\u003e25\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFig. 5b illustrates the changes in developed and agricultural land in South Korean coastal catchments since 1990 and their corresponding impact on vulnerability to offshore contamination. Note that the North Korea region was excluded from the study due to limited access to datasets. The overall proportion of developed and agricultural land has consistently increased from 1990 to 2020. Specifically, the developed area has continuously expanded, while agricultural land has steadily decreased. These changes have exacerbated the vulnerability of offshore contamination-prone regions by 38% since 1990 with the issue notably concentrated in the western and southern coastal regions.\u003c/p\u003e\n\u003cp\u003eThe analysis of GRACE TWS anomalies\u003csup\u003e26\u003c/sup\u003e also reveals a decreasing pattern of groundwater across coastal catchments. Extended Data Fig. 2 depicts Fig. S2 depicts the anomalies in TWS (mm) over coastal catchments from GRACE during 2002\u0026ndash;2016, along with their piecewise linear trends. TWS represents an integrated measure of the terrestrial water budget, encompassing groundwater, soil moisture, surface water, ice, snow, and water in vegetation. While TWS does not directly measure groundwater storage, changes in groundwater storage trends can be identified through TWS fluctuations. Coastal catchments do not contain streams, and TWS is more similar to groundwater storage compared to non-coastal catchments. The figure indicates no significant change until 2011, but from 2011 to 2016, a notable depletion of TWS (-0.79 mm/month) is evident. This issue primarily arises as domestic agriculture shifts towards high-value facility farming, leading to increased groundwater usage in these coastal areas.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImplications for expanding the perspective\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe outcomes of this research provide a fundamental foundation and support for a nationwide coastal vulnerability monitoring system. Our regional LSMs enable the continuous assessment of regional recharge rates and provide land-derived SGD rates along the coast of the Korean Peninsula. To enhance the accuracy of SGD rates using LSM approaches, it is essential to integrate local meteorological forcing datasets and land surface parameters into our regional LSM. This integration will help derive hydrologic variables relevant to SGD and allow for more precise topography for improved delineation of coastal catchments. Additionally, incorporating groundwater flow models on a local scale is necessary to explicitly address lateral groundwater flow.\u003c/p\u003e\n\u003cp\u003eOur LSM-based SGD estimations should be integrated into the existing groundwater measurement network. The Groundwater Information Management and Service Center (https://www.gims.go.kr) must carefully consider various SGD management factors. In addition to field measurements, satellite observational data and remote sensing techniques can complement proactive coastal vulnerability monitoring alongside the LSM\u003csup\u003e27\u003c/sup\u003e. GRACE data are valuable for providing groundwater storage anomalies across coastal catchments. The thermal infrared sensors of optical satellite missions can resolve the spatial variation of SGD rates and detect potential groundwater discharge areas along the coast of the Korean Peninsula.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eEstimation of fresh SGD\u003c/h2\u003e \u003cp\u003eCoastal catchments for fresh SGD were identified by manipulating the HydroSHED 15-arc second product (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.hydrosheds.org/\u003c/span\u003e\u003cspan address=\"https://www.hydrosheds.org/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Note that the selected coastal catchments are designed to exclude streams by construction. Instead, they are situated between established stream-coast intersections. The coastlines were delineated through the extraction of polyline products utilizing feature type attributes.\u003c/p\u003e \u003cp\u003eWe derive the adjusted net recharge rate by averaging the infiltrating runoff from three LSMs: Noah v3.9\u003csup\u003e32,33\u003c/sup\u003e, Noah-MP v4.0.1\u003csup\u003e34,35\u003c/sup\u003e, and JULES v5.5\u003csup\u003e36,37\u003c/sup\u003e. The three LSMs encompass a blend of models featuring notable variations in parameterizations and model physics\u003csup\u003e38\u003c/sup\u003e. The LSMs were run using a 15-minute timestep over a 37-year period (1980\u0026ndash;2016) at a spatial resolution of 1 km. The initial conditions for the simulation were established by running the LSMs from 1980 to 2016 twice, followed by a reinitialization in 1980. KLDAS was used as a driving force for the LSMs. The KLDAS encompasses the entirety of the Korean Peninsula, spanning from 33 to 44 degree north and 124 to 132 degree east. The KLDAS operates at a 1-km spatial resolution, incorporating local precipitation forcing datasets and soil texture maps. The recharge rate (\u003cem\u003er\u003c/em\u003e) for each grid cell was calculated as the average of daily infiltrating runoff, taking into account land cover types and including coastal catchments within the LSMs. The annual recharge volume for each coastal catchment was calculated by multiplying the catchment area (\u003cem\u003eA\u003c/em\u003e) by the annual recharge closest to the catchment centroid. Finally, to derive the fresh SGD flux (m\u0026sup2;/year), the annual recharge volume was divided by the corresponding coastline length (\u003cem\u003eL\u003c/em\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eSGD\u003c/em\u003e (m\u003csup\u003e2\u003c/sup\u003e/year)\u0026thinsp;=\u0026thinsp;\u003cem\u003er\u003c/em\u003e (m/year) \u0026times; \u003cem\u003eA\u003c/em\u003e (m\u003csup\u003e2\u003c/sup\u003e) / \u003cem\u003eL\u003c/em\u003e (m) (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eWe simplify our calculations by excluding groundwater contributions from upland catchments to coastal catchments, which may lead under-estimated fresh SGD. Additionally, human activities such as groundwater pumping (e.g., for irrigation and urban water supply) are neglected, which can lead to high estimation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eMann-Kendal trend test\u003c/h2\u003e \u003cp\u003eThe Mann-Kendall test, a non-parametric technique applied to evaluate monotonic trends in environmental datasets such as climate or hydrological data\u003csup\u003e39\u003c/sup\u003e, employs the \u003cem\u003eS\u003c/em\u003e statistic to determine the existence and extent of upward or downward patterns observed over time:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$S={\\sum }_{k=1}^{n-1}{\\sum }_{j=k+1}^{n}sign({x}_{j}-{x}_{k})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003ex\u003c/em\u003e represents the time series variable, with subscripts j and k denoting observation times. The \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(sign({x}_{j}-{x}_{k})\\)\u003c/span\u003e\u003c/span\u003e function yields values of +\u0026thinsp;1, 0, or -1, indicating increasing, no, and decreasing trends, respectively. The \u003cem\u003eS\u003c/em\u003e values are scaled to a range of [-1, 1] for improved interpretability. The null hypothesis posits that there is no statistically significant trend in the data, with significance set at a level of 5% (or 95% confidence level).\u003c/p\u003e \u003c/div\u003e\u003cp\u003e\u003cstrong\u003eEstimation of coastal vulnerability to offshore contamination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFollowing the ref. 14, we classified coastlines as susceptible to groundwater contamination when the proportion of developed and agricultural land surpassed the average (38.7%) and the fresh SGD flux exceeded the average (279 m\u003csup\u003e2\u003c/sup\u003e/year). Our vulnerability criteria generally apply if onshore aquifer contaminant concentrations increase alongside the fraction of developed land, and if coastal supply rates rise with fresh SGD rates, although multiple factors can influence contaminant flux to the coast.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo determine the percentage of developed and agricultural land in South Korean coastal catchments, we utilized the 2010 Land Cover Map from the Ministry of Environment of South Korea (https://egis.me.go.kr), which categorizes land into seven major types at a 30-meter resolution. For North Korea, we extracted land fraction data using the Moderate Resolution Imaging Spectroradiometer (MODIS) Land Cover Type (MCD12Q1) V6.1 2010 dataset\u003csup\u003e36\u003c/sup\u003e. The MODIS MCD12Q1 provides annual global land cover maps at a 500-meter resolution from 2001 to the present. We converted the raster data to a polygon shapefile and calculated the total areas of developed and crop land within each catchment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEstimation of coastal vulnerability to\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003esaltwater intrusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo assess vulnerability to saltwater intrusion in South Korea, with the exception of Jeju, we utilized data from the 2010 Marine Infiltration Survey Report, compiled by the Korea Rural Community Corporation (\u003ca href=\"https://www.groundwater.or.kr\"\u003ehttps://www.groundwater.or.kr\u003c/a\u003e). This report relied on data collected from 107 in-situ gauges and categorized vulnerability into four stages (interest, attention, caution, and serious) based on parameters such as electrical conductivity, its variations, and changes in reservoir levels. Similarly, for the Jeju Island region, we sourced information from the 2022 Groundwater Monitoring Report, prepared by the Jeju Groundwater Research Center (https://water.jeju.go.kr). Note that we did not assess the vulnerability to saltwater intrusion in North Korea due to limited available data, and the in-situ gauges do not cover all coastal catchments in South Korea.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImpact of decadal land use changes\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eon coastal vulnerability to offshore contamination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo evaluate the proportion of developed and agricultural land in South Korean coastal catchments over time, we analyzed four sequential datasets (1990, 2000, 2010, and 2020) from the Land Cover Map (Fig. 5b). This methodology mirrors the approach used for assessing offshore contamination vulnerability. We established specific thresholds for averaged fresh SGD flux corresponding to the year of SGD estimation. However, due to the study\u0026apos;s timeframe, the 2020 data was beyond our scope. To address this, we utilized the 2012 SGD estimates as a proxy for the 2020 estimates, given the similarity in precipitation patterns and spatial distribution between 2012 and 2020.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTWS anomalies\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;over the coastal catchment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe utilize three distinct GRACE products, which are provided monthly on 1\u0026deg; horizontal resolution grids by the University of Texas Center for Space Research, Jet Propulsion Laboratory, and German Research Centre for Geosciences. These products are derived from the RL06v04 spherical harmonics fields\u003csup\u003e37\u003c/sup\u003e. To extract TWS anomalies over the coastal catchments, we interpolated the GRACE datasets to fit the 1-km LSM grid and extracted the value closest to the catchment centroid.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHydroSHED 15-arc second products were downloaded from the HydroSHED website (https://www.hydrosheds.org/). KLDAS datasets can be obtained by requesting them from the authors. The land cover map for South Korea was downloaded from the Ministry of Environment of South Korea (https://egis.me.go.kr). The MODIS MCD12Q1 V6.1 was obtained from the Land Processes Distributed Active Archive Center (https://lpdaac.usgs.gov/products/mcd12q1v061/). Gauge datasets for saltwater intrusion in South Korea are available from the Korea Rural Community Corporation (https://www.groundwater.or.kr). Saltwater intrusion observations for Jeju can be found at the Jeju Groundwater Research Center (https://water.jeju.go.kr). GRACE datasets were downloaded from NASA JPL GRACE Tellus (https://grace.jpl.nasa.gov). \u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe three LSMs (Noah v3.9, Noah-MP v4.0.1, and JULES v5.5) are available via the NASA Land Information System (https://github.com/NASA-LIS/LISF).\u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the National Research Foundation of Korea (NRFK) and funded by the Korean Government (2021R1A2C100578013) and Yonsei University Future-Leading Research Initiative (2023-22-0128). \u003c/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests. \u003c/p\u003e\n\n"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBurnett, W. C., Aggarwal, P. K., Aureli, A., Bokuniewicz, H., Cable, J. 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Res.\u003c/em\u003e \u003cstrong\u003e48\u003c/strong\u003e, W04531 (2012).\u003c/li\u003e\n\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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4558926/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4558926/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe impact of climate change on fresh submarine ground discharge (SGD) variation on the Korean Peninsula challenges coastal regions, making them susceptible to environmental degradation and economic impacts. This study provides the first regional estimates of fresh SGD along the entire coast of the Korean Peninsula from 1980 to 2016, utilizing established water balance methods. Our results indicate that the western and southern coasts of South Korea experience higher fresh SGD rates due to greater net precipitation compared to the North Korean region. The impact of drainage length is evident when examining the East and West coasts. Notably, substantial tidal flats on the West coast, where tidal differences significantly influence high SGD rates, are particularly significant. Climate change affects fresh SGD variation, with South Korea's western and southern coasts showing rising trends in spring and winter, while North Korean coastal watersheds display a consistent increase across all seasons. Our findings highlight the vulnerability of Korean coastal regions to climate change and land use development, affecting 15% of the coastline. Specifically, the increased development and agricultural land in South Korean coastal catchments have exacerbated vulnerability by 38% since 1990, driven by economic growth, population expansion, and shifts in cultivated crops.\u003c/p\u003e","manuscriptTitle":"Impact of Submarine Groundwater Discharge, Climate Change, and Land Use on Korea’s Coast","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-23 06:04:29","doi":"10.21203/rs.3.rs-4558926/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"12846b32-4cc8-4748-a5bd-ab0cae603123","owner":[],"postedDate":"July 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":33574460,"name":"Earth and environmental sciences/Hydrology"},{"id":33574461,"name":"Earth and environmental sciences/Climate sciences/Hydrology"}],"tags":[],"updatedAt":"2025-02-15T08:05:45+00:00","versionOfRecord":{"articleIdentity":"rs-4558926","link":"https://doi.org/10.1038/s43247-025-02084-9","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2025-02-14 05:00:00","publishedOnDateReadable":"February 14th, 2025"},"versionCreatedAt":"2024-07-23 06:04:29","video":"","vorDoi":"10.1038/s43247-025-02084-9","vorDoiUrl":"https://doi.org/10.1038/s43247-025-02084-9","workflowStages":[]},"version":"v1","identity":"rs-4558926","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4558926","identity":"rs-4558926","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}