Influence of Urbanization and Climate on Surface Water Diversions in a Semi‐Arid Basin

ABSTRACT Irrigated lands in arid and semi‐arid regions are rapidly urbanizing and impacting water resource management in various ways. Here, we examined temporal trends in canal diversions to irrigation districts that have undergone varying degrees of urbanization using Bayesian autoregressive generalized linear mixed models in the Lower Boise River Basin (LBRB), located in southwest Idaho. We found that urbanization had a negative effect on total diversion volumes, while interannual variability in diversions was more correlated to climate variables than urbanization, which had no effect at that scale. Increased precipitation and temperature led to decreased irrigation diversions through time, but the effects were small, while increased evapotranspiration is associated with increased diversion volumes. The direction and magnitude of urban and climate effects varied from other urban water usage studies, which could stem from systematic or model structure differences, suggesting the need for further review across urban irrigation water usage studies. Leveraging different model structures enables exploration of relationships across scales and will allow us to align our modeling tools with scales relevant for decision‐making. Communicating how and why this heterogeneity and associated uncertainty are important to consider will be imperative for facilitating adaptive water management in times of rapid change.