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Comparing the Influence of Global Warming and Urban Anthropogenic Heat on Extreme Precipitation in Urbanized Pearl River Delta Area Based on Dynamical Downscaling

K. Fung,C. Tam,Tsz-cheung Lee,Ziqian Wang

Published 2021 in Journal of Geophysical Research: Atmospheres

ABSTRACT

This study compares the impacts of global warming and intense urban anthropogenic heat (AH) on extreme hourly precipitation over the Pearl River Delta (PRD) megacity, located in coastal South China. Using the cloud‐resolving Weather Research and Forecasting (WRF) model coupled with the single‐layer urban canopy model (SLUCM), three downscaling experiments were carried out: the first (second) having zero (300 W/m2) as diurnal maximum AH values prescribed over PRD urban grids, under the current climate conditions. The third experiment with diurnal maximum AH of 300 W/m2 under future projected climate representative concentration pathway (RCP) 8.5. Boundary conditions were derived from PRD extreme rainfall episodes, identified from the Geophysical Fluid Dynamics Laboratory Earth System Model (GFDL‐ESM2M) historical and RCP8.5 runs. Global warming forcing leads to ∼20% to more than 100% increase in the probability of hourly precipitation with the magnitude of 20–100 mm/hr over urban locations. The enhancements from intense AH forcing were similar. However, two forcings have distinct signatures in modulating the thermodynamic environment. Warming due to AH is limited to the lowest 1 km above ground, while global warming warms up the whole troposphere. Intense AH results in enhanced convective available potential energy (CAPE) and reduced convective inhibition (CIN) within the megacity, allowing convection to be triggered more easily and with more vigor. On the other hand, global warming enhances CAPE and CIN, over both urban and rural areas. Our results highlight the different mechanisms of AH and global warming in exacerbating extreme urban rainfall, despite the similar impacts on the rainfall intensity.

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