Assessing future water supply and demand under climate change in an agriculture-dominated watershed

Authors: PHUNG, QUANG - University Of Missouri; THOMPSON, ALLEN - University Of Missouri; Baffaut, Claire; COSTELLO, CHRISTINE - University Of Missouri; Sadler, Edward

Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: There is need to improve our understanding of the impact of climate variability and change on hydrologic processes at the watershed scale. This is important, particularly for land managers and policy makers, in making better-informed decisions to assess adaptation strategies and to ensure that all sectors and populations can meet projected water demand. The Missouri Salt River Basin was chosen for this study due to its unique soil and mixed land use. It is dominated by high clay content soils making it sensitive to changes in the hydrologic condition. While numerous studies have examined hydrologic processes around this region, only a few have analyzed linkages between climate and the consequence of these changes to water allocation. One of the greatest potentials to maintain viable crop and livestock economies is to continue making gains in production efficiency, particularly in the area of rain-fed crops with the potential of increasing irrigation. Therefore, the objective of this study is to evaluate projected future water supply and demand in this watershed given projections of future climate and changing land management practice. Temperature and precipitation projections for two representative concentration pathways (RCP 4.5 moderate CO2 level and RCP 8.5 high CO2 level) were obtained from twenty general circulation models and were statistically downscaled to better represent local conditions. These 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. Possible outcomes for the near (2020-2039) and far (2040 2059) future scenarios were determined. The RCP ensembles showed precipitation increased from 4% to 7% for both near and far future scenarios. Ensemble result from RCP 4.5 scenarios projected increased annual water yield (7%) in far future. Seasonal analysis for RCP 4.5 indicated water yield increased in spring (+25%) and fall (20%), and decreased in winter (26%), while summer showed minimal changes. Similar trends were observed for RCP 8.5. Using hydrologic output simulations from SWAT, evaluation of water allocation strategies will be performed using the water evaluation and planning (WEAP) model. By selecting priority water use strategies, WEAP enables review of potential conflicts among users through scenario-based approaches. Operating on the basic principle of water balance accounting, a range of inter-related water issues facing water users, including multiple surface/groundwater sources, sectoral demand analyses, water conservation, water allocation priorities, and general reservoir operations, are being evaluated. Based on USDA census data for 2012, irrigation area for crop and pasture, and livestock headcount were obtained. For this study, scenarios with different rate of irrigation expansion for crop and pasture areas will be evaluated. The Ag Census data from 1997, 2002, and 2007 were analyzed to obtain the highest reported number of livestock in each county. The historical maximum was then assumed to be the build-out inventory for 2060 to account for fluctuations due to unforeseen circumstances in the future. The outcome of this project could be used to develop guidelines for future water allocation planning.