Impacts of City Shape on Rainfall in Inland and Coastal Environments

Abstract

Abstract Urbanization manifests rainfall anomalies both in and around the city. While prior studies have assessed the effect of urban expansion as well as city size, little is known about the impact of city shape on rainfall. Here, idealized large eddy simulations coupled with the Weather Research and Forecasting model are conducted to bridge the knowledge gap. Results indicate differences in the timing for urban‐induced rainfall in the inland versus coastal environment. This is associated with contrasting diurnal cycles of vertical velocity and cloud water mixing ratio driven by the land‐sea breeze. The impact of city shape on rainfall is more evident in the coastal environment, as buoyancy flows arise from cities alter the interactions between urban‐rural circulation and sea breeze. A circular city shows nearly 22.0% larger rainfall accumulation and 78.6% greater rainfall intensity compared to a triangular city over urban surfaces. The rainfall anomaly is caused by different urban‐rural circulations over various city shapes. The strong low‐level convergence over circular cities favors efficient upward moisture transport and deep convection. Results highlight the need for considering city shape for coastal urban planning, as a potential adaptation strategy to manage rainfall under future climate. The coarse‐resolution climate models that represent the impervious surface area but not the right shape would have a higher uncertainty in simulating rainfall changes.

Keywords

• city shape
• large eddy simulation
• moist convergence
• urban rainfall