Regional Impacts of Urban Irrigation on Surface Heat Fluxes and Rainfall in Central Arizona

Rapid urbanization over Phoenix has resulted in increased water consumption for maintenance of green spaces and heat stress mitigation. The hydrometeorological impact of urban irrigation is not well understood and is the principal objective of this study. Our results are based on high-resolution numerical experiments using the Weather Research and Forecasting model. A simple irrigation scheme is implemented into the Weather Research and Forecasting model to represent changes in soil moisture due to irrigation. A monthlong simulation using the Weather Research and Forecasting model with irrigation shows improved model performance in representing the regional water and energy cycle. Comparisons of model simulations with and without irrigation highlight the regional impacts of urban irrigation on surface heat fluxes and rainfall variability over Phoenix. There is a strong modulation of irrigation on surface energy partitioning over both irrigated and nonirrigated areas. Irrigation increases (decreases) surface latent (sensible) heat fluxes by enhanced evapotranspiration over irrigated areas, with opposing changes presented over nonirrigated areas. Irrigation contributes little to the domain-average rainfall accumulation, but can noticeably modify its spatial distribution, with increased rainfall over the downwind mountainous regions and decreased rainfall over the irrigated areas. Irrigation-induced rainfall anomalies can be tied to strengthened thermal gradients and induced changes in surface pressure fields, which lead to perturbations on large-scale flow and its interactions with complex terrain. Our results shed light on the hydrometeorological impacts of increasing anthropogenic water use driven by urbanization and highlight the importance of accurate representations of land surface processes in better characterizing land-atmosphere interactions in arid/semiarid regions.