Impacts of Large-Scale Urbanization and Irrigation on Summer Convective Precipitation and Heat Stress
Urbanization and irrigation have significant impacts on the environment and human society by generating opposing perturbations in the boundary layer atmosphere. Urbanization is commonly associated with warmer and drier air, while irrigation tends to create cooler and moister conditions. However, their impacts on extreme weather events remain uncertain. This study investigates the effects of urbanization and irrigation in the United States east of the Rocky Mountains on summer convective precipitation and heat stress using convection-permitting regional model simulations with and without urbanization or irrigation. To assess the impact, a feature tracking algorithm is employed to identify different types of precipitation from mesoscale convective systems (MCSs), isolated deep convection (IDC), and non-convective systems. The results show that urbanization suppresses all three types of precipitation in the Mid-Atlantic region due to reduced water vapor content and convective available potential energy. Conversely, irrigation enhances IDC and non-convective precipitation while suppressing MCS precipitation. Further analysis of the MCS and IDC initiation locations reveals that irrigation hampers Mid-Atlantic region precipitation produced by MCSs initiated in the Great Plains and Midwest. Irrigation induces a mid-level cyclonic circulation anomaly centered in the Southeast, impeding the eastward propagation and development of MCSs originating from the Great Plains. Meanwhile we find that irrigation generally alleviates summertime heat stress, but its effectiveness varies by climate zone and the metrics used to define heat stress. Additionally, we explore the interplay between urbanization and irrigation effects on urban heat stress, highlighting the complexities in accurately interpreting their impacts.