Responses of Hydrological Processes to Future Climate Variability and Agricultural Land Afforestation in a Humid River Basin

Abstract

Changes in climate conditions and land‐use patterns exert significant influences on hydrological processes in agriculture‐dominated watersheds, with direct implications for regional water and food security. Although afforestation has been implemented in many agriculture‐dominated watersheds in the United States, the response of key hydrological processes to afforestation under future climate conditions remains poorly understood. In this study, we simulated the dynamics of three major hydrological variables–evapotranspiration (ET), groundwater recharge and water yield–in the Lower Mississippi Alluvial Valley (a humid river basin) using the SWAT+ model under 265 scenarios combining future climate conditions and afforestation levels. Our results show that, relative to the early 21st century (2000–2019), climate change alone is projected to decrease water yield by 1.4%–2.2% ( p  > 0.05) and groundwater recharge by 15.1%–21.3% ( p  < 0.001), while increasing ET by 7.2%–10.6% ( p  < 0.001) by the late 21st century (2080–2099). Afforestation is also expected to have significant impacts on watershed hydrological processes. For instance, a 20% expansion in forest cover is projected to decrease water yield by 7.2%, while ET and groundwater recharge are projected to increase by 3.6% and 6.2% under SSP245, respectively. These findings indicate that large‐scale afforestation in humid regions can significantly reduce water yield while increasing groundwater recharge to the shallow aquifer water storage. Afforestation planning should therefore be spatially targeted and coordinated with irrigation and groundwater management to balance recharge gains against reductions in water yield.