Abstract
Urbanization and global warming are two of the major human impacts on the environment. The Urban Heat Island (UHI) effect can change precipitation patterns. Global warming also leads to changes in precipitation and especially an increase in intensity and frequency of extreme precipitation. With urbanization expected to grow in the future, the role of UHI in a warmer climate is an important research question. We present results from 20-year long regional convection-permitting model simulations that include the UHI effect, run for historical and future climates for two megacities, Paris and Shanghai. In the warmer future climate, urban-induced precipitation is found to decrease compared to the historical climate, for both mean and extreme precipitation, with large uncertainties due to natural variability. The mean precipitation increase due to UHI in Paris is 2.2± 1.4% and 1.8 ± 1.3% for historical and future conditions, respectively. Shanghai has slightly weaker mean precipitation change than Paris at present and no change in the future. The future reduction of the urban effect is found to be caused by a decrease in summer precipitation for both cities. Interannual variability in precipitation due to UHI is larger for Shanghai than Paris. The UHI effect on extreme precipitation is also reduced in the future climate and the area with precipitation increase is more concentrated. The general increase in extreme precipitation due to global warming, in combination with the precipitation redistribution due to UHI, underline the importance for future urban planning to mitigate damage caused by extreme precipitation events.
Highlights
Urban Heat Islands (UHI) are formed when cities have higher temperatures than surrounding rural areas (Oke 1982; Arnfield 2003)
Even though the temperature difference due to UHI shown for the two time periods is comparable, the historical conditions (1986–2005) UHI has a bigger impact on mean precipitation increase over the urban grid cells compared to end of the century conditions (2081–2100) for both cities
We present results on the role of the UHI on mean and extreme precipitation, simulated by a convection-permitting regional model driven by a global climate model for a historical and a future scenario for Paris and Shanghai
Summary
Urban Heat Islands (UHI) are formed when cities have higher temperatures than surrounding rural areas (Oke 1982; Arnfield 2003). With global warming the hydrological cycle amplifies and causes changes in mean and extreme precipitation that differ globally (Douville et al 2021; Pfahl et al 2017; Hodnebrog et al 2019). This leads to an increase in intensity (Fischer and Knutti 2016) and frequency of extreme precipitation (Myhre et al 2019). As more people live in impenetrable urban areas, in a warming climate with more extreme precipitation, the added effect of UHI on precipitation is of high importance for future urban planning
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