Urban-enhanced precipitation in the Maritime Continent from a convection permitting model.

Urban-enhanced precipitation in the Maritime Continent from a convection permitting modelThis study quantifies the effect of urban areas on precipitation at local scales over the western Maritime Continent using a regional climate model operating at convection permitting spatial resolution. The Weather Research and Forecasting model coupled with an Urban Canopy Model was used to simulate the atmosphere of the region over a 5-year period at 2-km spatial resolution. Two separate simulations with and without urban areas were completed to investigate the influence of cities on rainfall. We analyze how urban areas modify the annual precipitation, as well as its diurnal cycle, which is a key feature of the Maritime Continent. Our results indicate that major cities intensify precipitation in the late afternoon. As a consequence, they strengthen the diurnal cycle and contribute to a significant increase in rainfall amounts. Examining urban-induced changes in temperature, humidity and wind provide an insight into the mechanisms that drive such effects. We found that the presence of cities modifies the local circulation. They constitute a source of heat at the surface, which destabilizes the atmosphere and brings moisture from the surroundings, especially from the ocean. Urban areas also reduce convective inhibition. Together, these processes increase near-surface moisture flux convergence and favor convective processes leading to an overall increase of precipitation over cities.