Analyzing the Impact of Reservoir Incorporation, Changing Land Cover, and Future Climate Change on Basin Response Using a SWAT Model

In this study, the impact of the inclusion of storage structures like reservoirs on the hydrological model performance using the Soil and Water Assessment Tool (SWAT) is analyzed. Additionally, land use land cover (LULC) change over a span of two decades from 2001 to 2021 on the water balance components of the lower Columbia River basin is also studied. Among different scenarios, considering the best performing model as the base model setup, future climate change impact on the hydrological response of the basin has been investigated in terms of changes exhibited by water balance components of the basin. In the present study, an improvement in runoff and model performance was observed because of the inclusion of reservoirs. It was also found that over the past twenty years, urban areas, grasslands, and agricultural lands have expanded by 145.12 km2, 627.34 km2, and 541.18 km2, respectively. In contrast, forest cover, barren lands, and pastures have decreased by 1,067.24 km2, 31.74 km2, and 719.05 km2, respectively, between 2001 to 2021. After incorporating reservoirs in the model, changes in the water balance components are observed. The runoff and groundwater were reduced by 16.95% and 11.57%, respectively, while evapotranspiration increased by 74.37% from 1992 to 2022. In terms of future climate change impact, Coupled Model Intercomparison Project (CMIP) climate models, CMIP5 and CMIP6, (Hadley Centre global environmental models HadGEM2-ES and HadGEM3-GC31, respectively) were used for comparative analysis of the hydrological response of the basin, where the CMIP6 model predicts an increase in surface runoff by 14.39% toward the end of the century. It is hoped that this study will help the water managers and administrators to identify the hydrological response units that have undergone major LULC changes and caused subsequent variations in the runoff.