Assessing future water supply and demand under climate variability in an agricultural watershed

Authors: PHUNG, QUANG - University Of Missouri; THOMPSON, ALLEN - University Of Missouri; Baffaut, Claire; COSTELLO, CHRISTINE - Pennsylvania University; SADLER, EDWARD - Retired ARS Employee

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2022
Publication Date: 9/28/2022
Citation: Phung, Q., Thompson, A., Baffaut, C., Costello, C., Sadler, E.J. 2022. Assessing future water supply and demand under climate variability in an agricultural watershed. Journal of the American Water Resources Association. Paper No. JAWR-20-0128-P. https://doi.org/10.1111/1752-1688.13059.
DOI: https://doi.org/10.1111/1752-1688.13059

Interpretive Summary: Climate change and increasing population are increasing demand for water and causing severe water shortages in many watersheds across the US Midwest. Decision makers need to understand the impact that long-term climatic trends may have on water allocation, particularly for watersheds with significant agricultural activity. The Missouri Salt River Basin (SRB) was chosen for this study due to its soil characteristics, because it is dominated by agriculture, and because it contains a major reservoir, Mark Twain Lake, which is the regional source of drinking water. The soils in SRB have high runoff potential and they are sensitive to overly wet and dry conditions. Most agricultural production is rain-fed, making the area vulnerable to temperature increase and precipitation shortage during the growing season. The objective of this study was to evaluate future water supply and demand in the SRB watershed given projections of future climate and changing land management practices. Future climate data, along with soils, land cover, land management, and topography were input to a computer simulation model that estimated crop water shortages and calculated flows into the reservoir for the near future (2020-2039) and mid-century (2040-2059). Water allocation strategies were evaluated with another computer simulation model to identify potential conflicts among users through scenario-based approaches. Results indicated that future water shortages could become more frequent and severe in the SRB under projected climate conditions. The future average annual unmet water demand, which is the difference between water demand and supply, was projected to double as a consequence of rising temperatures and irregular precipitation, from 3 to 6 million m3. An irrigation expansion scenario in which irrigated cropland increased from 2.5% to 10% of the watershed cropland resulted in 38.5 million m3 of unmet water demand. However, allowing water withdrawals from Mark Twain for agriculture purposes would help alleviate the projected water shortages.

Technical Abstract: Climate change and population driven pressure are increasing demand for water and causing severe water shortages in many watersheds across the US Midwest. Therefore, the need exists to improve our understanding of the impact of climate variability and long-term trends on water allocation, particularly for watersheds with significant agricultural activity. The Missouri Salt River Basin (SRB) was chosen for this study due to its soil characteristics, agriculturally-dominated land use, and because it contains a major reservoir, Mark Twain Lake, which is the regional source of drinking water. The SRB is dominated by claypan soils that are sensitive to overly wet and overly dry conditions, and have high runoff potential. Most agricultural production is rain-fed, making the area vulnerable to temperature increase and precipitation shortage during the growing season. The objective of this study was to evaluate future water supply and demand in the SRB watershed given projections of future climate and changing land management practices. Future climate data, along with soils, land cover, land management, and topography were input to the Soil and Water Assessment Tool (SWAT), a process-based hydrologic simulation model, to evaluate hydrologic impacts for the near future (2020-2039) and mid-century (2040-2059). Evaluation of water allocation strategies was performed using the Water Evaluation and Planning (WEAP) model to identify potential conflicts among users through scenario-based approaches. Results indicated that future water shortages could become more prominent in the SRB under projected climate conditions. The future average annual unmet water demand, which is the difference between water demand and supply, was projected to double as a consequence of climate change, from 3 to 6 million m3. An irrigation expansion scenario in which irrigated cropland increased from 2.5% to 10% of the watershed cropland resulted in 38.5 million m3 of unmet water demand. However, permitting water to be withdrawn from Mark Twain Lake for agricultural purposes would help alleviate the projected water shortage problem.