Future Water Availability: Impacts of Climate Change and Water Demand

Global climate change can alter precipitation patterns and temperatures, impacting regional hydrologic cycles and river flows, potentially leading to supply deficits during peak use periods. Future water use patterns may shift due to increased demand for food and energy production driven by population growth. Anthropogenic activities, such as agriculture and power generation, can degrade water quality, affecting its availability for various uses. This study evaluates the impacts of climate change and water demand on water availability in the Kaskaskia River watershed, Illinois, USA. The Kaskaskia River, the second largest river in Illinois, flows southwest to its confluence with the Mississippi River. Lake Shelbyville and Carlyle Lake, the two principal reservoirs on the mainstem of the Kaskaskia River, serve as primary sources of water supply in the region. Both reservoirs, federally owned, are operated and managed by the United States Army Corps of Engineers (USACE) to meet water demand in the watershed, including water supply, flood control, navigation, and recreational needs. The land use of the Kaskaskia River watershed is primarily agricultural, with row crops covering more than 60 percent of the area. Two-thirds of the watershed soil has moderately low infiltration capacity. The region receives an average annual precipitation of 1,041 millimeters. A detailed hydrologic model of the Kaskaskia River watershed was developed, incorporating modifications to watershed process algorithms and implementing a daily target release method for the reservoirs, which significantly improved storage and outflow simulations. The modeling process involved developing four subwatershed models with HUC12 as their subbasins and further subdividing subbasins into hydrologic response units (HRUs) to enhance simulation granularity. The model also incorporated Lake Shelbyville and Carlyle Lake, along with point sources and water withdrawals. Calibration and validation across the models and reservoirs, involving sensitivity analysis and automatic calibration, yielded good performance metrics. The model accurately simulated streamflow and reservoir dynamics, providing reliable predictions. The calibrated models were integrated into a single Kaskaskia River watershed model, which was then applied to simulate future water use and climate scenarios, offering insights into potential hydrologic impacts. The findings revealed that climate change significantly impacts river flows and reservoir storages, while water use has minimal effects. Under RCP2.6, RCP4.5, and RCP8.5 scenarios, minimum storage volumes of both reservoirs are projected to decrease over the next 25 and 50 years, while maximum storage volumes are expected to increase. Future water yields of both reservoirs are anticipated to exceed current yields, underscoring the need for sustainable water resource management amidst climate variability and changing demands. The study highlights the importance of adaptive water resource management to mitigate climate change impacts and ensure long-term sustainability.