This collection comprises the data, codes, analyses and results for my thesis. See the thesis in USU Digital Commons for more information.

PUBLIC ABSTRACT

According to the United States Geological Survey, irrigation represents about 80% of the freshwater withdrawn in Utah. On average, Utah is the second driest state in the U.S., with drier conditions projected throughout the century. Periods fluctuating between drought and flood are typical in the region. Understanding what factors affect Utah’s largest water user can inform sustainable irrigation practices, which could lead to conservation of Utah’s vital surface and groundwater. National, regional, and state analyses have identified total irrigated acreages, more efficient irrigation technologies, and freshwater availability as significant factors of irrigation withdrawals. This study sought to bring these findings up to date in Utah, and validate them at state, sub-state, and county levels. Utilizing Kendall’s Tau-b correlation test, factor relationships were assessed between the survey’s irrigation withdrawal and acreage data, as well as water year, season, and monthly freshwater availability key indicators including natural stream flows, reservoir levels, precipitation, and ambient temperatures. At the state level, no significant correlations were found between total irrigation withdrawals and total, or sprinkler, irrigated acres. This could indicate that practices such as fallowing fields, or converting to sprinkler systems, may not significantly reduce irrigation withdrawals. Relatively few significant results were found between irrigation withdrawals and water year key indicators, suggesting that historical infrastructure and practices have been adequate at overcoming annual freshwater availability fluctuations. Total and surface irrigation withdrawals were significantly negatively correlated with ground withdrawals, suggesting that conjunctive management principles have played a key role mitigating annual freshwater availability fluctuations. Groundwater stores have been overdrawn in many areas of the state, and this practice may not be sustainable under projected drier conditions. With further analyses, some significant correlations between irrigation withdrawals, and early months and seasons’ precipitation and ambient temperatures may be utilized in irrigation demand projections. Though sub-state results were similar with statewide results, county results varied, demonstrating the importance of finer scales of analyses and localized decision making. It also highlights areas that may be more affected by freshwater availability, as well as the many unique irrigation withdrawal reduction opportunities that exist within areas of Utah.