Impacts of Climate Change and Land Use Change on the Groundwater Recharge in Siem Reap, Cambodia

Primarily driven by international tourism, Siem Reap of the Kingdom of Cambodia is of very high economic potential. However, along with the change in land use due to urbanization, climate change is also seen to reduce the flow along the Siem Reap River significantly. With the province already experiencing water supply deficit, groundwater becomes an important source of water. In light of sustainable groundwater management, this study assessed the impacts of climate and land use changes on the groundwater recharge (GWR) over Siem Reap under two shared socioeconomic pathways (SSP) - SSP2 as the middle of the road scenario and SSP5 as the fossil-fuel development scenario. Climate data from 7 CMIP6 GCMs were evaluated and among them, CanESM5, EC_Earth3, and MIROC6 captured the observed data best. Bias-corrected data show a general increase in precipitation, an average increase in maximum temperature of 0.024°C/year and 0.049°C/year under SSP2-4.5 and SSP5-8.5, respectively, and an average increase in minimum temperature of 0.025°C/year and 0.055°C/year under SSP2-4.5 and SSP5-8.5, respectively. Land use change analysis using global datasets showed that the urban area increased by 373% (4.95 to 23.4 km2) from 2004 to 2019 at the expense of forests and shrublands. Using DynaCLUE model, future land use maps were generated. And by using SWAT, the impacts of climate change and land use change on groundwater recharge were simulated. It was found that from the baseline GWR rate of 303 mm/year, future GWR could increase to 360 to 442 mm/year under SSP2-4.5 scenario and up to 375 to 434 mm/year under SSP5-8.5 scenario. Analysis using constant land use shows that GWR is higher when land use change is not considered, highlighting the importance of land use planning.