Bridget Bittmann

How are Urbanization and Climate Affecting Irrigation Water Demand in the Lower Boise River Basin?

Abstract

Regions across the western US are rapidly urbanizing, causing substantial land use and land cover change in historically agricultural areas. In the Lower Boise River Basin of southwestern Idaho, this change in land use has caused subsequent shifts in irrigation water usage, resulting in water that was historically used to irrigate crops now being spread across lawns and parks. Simultaneously, climate change is producing rapid warming, variable changes in precipitation, prolonged drought, and increased rates of evapotranspiration. Water managers currently do not have the information as to how both land use change and climate variability is impacting the irrigation water demand in the Lower Boise River Basin, which limits their ability to plan for future irrigation seasons as population growth continues. The goal of this study was to analyze surface water irrigation diversions in the Lower Boise River Basin to inform water management on the extent that land use change and climate are impacting annual irrigation deliveries. We used a Generalized Linear Mixed Model to estimate the effect of urban area, precipitation, temperature, evapotranspiration, and reservoir storage water use on the amount of water discharging into irrigation canals from 1987 to 2020. Model results showed that climate affected diversion flows while urbanization did not have any impact on diversion flows, indicating that urbanization is not changing the amount of water people are using. Discussion with local water managers has been crucial to better understanding the drivers for potential change in irrigation water demand and to disseminate and validate the results of this study. Local managers may use these results to better plan for future water demand in the basin with ongoing growth and climate change.