Effect difference of climate change and urbanization on extreme precipitation over the Guangdong-Hong Kong-Macao Greater Bay Area

Increasing extreme precipitation caused by climate change and human activities may have severe consequences on people's lives and property. In this study, the effect difference of urbanization, climate change and their compound effect on the annual and seasonal extreme precipitation under various Shared Socioeconomic Pathways are investigated using a convection-permitting (4 km) Weather Research and Forecasting model in the mega urban agglomeration. The enhancement effects of urbanization and climate change on extreme precipitation are also compared in the near future (2021–2050) and far future (2071–2100) periods of various Shared Socioeconomic Pathways-Representative Concentration Pathways (SSP-RCP) emission scenarios. The Guangdong-Hong Kong-Macao Greater Bay Area (GBA), a subtropical coastal world-class urban agglomeration in China, is taken as a representative in this study. The results indicate that, annual extreme and total precipitation will be more intensive and more frequent at regional scale along with rising long-lived greenhouse gas (LLGHG) concentration, while future urbanization exacerbates precipitation at local scale. Urban-induced total precipitation increases in the downwind areas and some urban areas of urban agglomeration, but still slightly decreases (all below 1.5%) over the entire study area. And more robust and stronger urban-induced signal in extreme precipitation characteristic is found in and around the urban areas where the total precipitation increases, as seen with an increase of >20% in amount and day number. In the compound scenarios, the interaction between urban and LLGHGs on precipitation was nonlinear and can be better explored by using convective permitting simulations. While urbanization can amplify or dampen local to regional precipitation, increased concentration of LLGHGs still make regional precipitation shift toward a general enhancement. Urbanization still has an impact on spatial distribution of precipitation despite a warming background climate. Additionally, seasonal heterogeneity of precipitation will be enhanced in all the future scenarios, especially in the future urbanization scenarios. The enhancement of urbanization (increase by about 42.1%, 38.0%, 14.0% in the precipitation amount, days and intensity respectively) on summer extreme precipitation change is greater than that of low-level LLGHG concentration (same as above, but increase by about 38.7%, 35.4%, 13.4%), despite their different mechanisms in altering extreme precipitation. The dominant factor of extreme precipitation varies with urbanization level and the LLGHG concentration. More attention should be paid to urban-induced precipitation changes under sustainable development scenarios with low-level LLGHG concentration. • The enhancement effects of urbanization and LLGHG on extreme precipitation are also compared in various emission scenarios and periods over the mega urban agglomeration. • Although urbanization can amplify or dampen local to regional precipitation, LLGHG still make regional precipitation shift toward a general enhancement. • More attention should be paid to urban-induced precipitation changes under sustainable development scenarios with low-level LLGHG emissions.