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

Abstract

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.

A Multiyear Assessment of Irrigation Cooling Capacity in Agricultural and Urban Settings of Central Arizona

“…Average daily LST differences were reduced for the daytime (0800 to 1700 local time) from 3.2°C to 0.3°C over croplands and from 4.2°C to 1.4°C over urban areas. Furthermore, this shows that VIC-IRR can capture the evaporative cooling effect of irrigation in a means consistent with prior observations (Templeton et al 2018) and modeling work (Yang et al 2019). The evaporative cooling effect is also compared to the diurnal cycle of air temperature (T air ) obtained from the forcing product for each land cover type.…”

“…As such, a fruitful avenue of research is to incorporate remotely sensed products to determine the spatiotemporal patterns of vegetation conditions in evaluations of ICC in other regions with outdoor water use. The impacts of these dynamics should also be taken into account when considering the impact of irrigation on atmospheric conditions, for instance, through coupled land-atmosphere modeling (e.g., Xiang et al 2018;Yang et al 2019).…”

Interplay Between Urbanization and Irrigation on Summer Climate in the Huang‐Huai‐Hai Plain, China

“…This study utilizes a relatively simple calculation to determine the irrigation time and the fixed irrigation amount was used, which might be further refined in future studies. Second, the rapid urbanization might also result in an increased water consumption so as to maintain green space and mitigate heat stress (Y. Yang et al., 2019). Since this paper highlights the regional climate, urban irrigation was omitted, and we assumed that irrigation only happened on cropland.…”

“…Second, the rapid urbanization might also result in an increased water consumption so as to maintain green space and mitigate heat stress (Y. Yang et al, 2019). Since this paper highlights the regional climate, urban irrigation was omitted, and we assumed that irrigation only happened on cropland.…”

Updating intensity–duration–frequency curves for urban infrastructure design under a changing environment

“…Because a feasible reason is the exacerbation of convection by local UHI, especially at the start of the rainfall events. Yang et al (2019) analyzed the impacts of urban irrigation (i.e., irrigation for public greenspaces) on surface heat fluxes and precipitation in central Arizona using a high-resolution WRF model with or without an irrigation scheme. They found that urban irrigation had little impact on the average precipitation volume, but can significantly alter the spatial distribution of precipitation.…”