Urbanization mitigates the intensification of summer wet heatwaves in China from 1970 to 2020

The urban heat island effect (UHI) exaggerates heat extremes, whereas the concurrent urban dry island effect (UDI) may mitigate heatwave risks. It remains unclear whether urbanization increases or decreases the risk of heatwaves at a large scale. Using daily meteorological observations provided by China Meteorological Data Service Center and urban-minus-rural method, this study analyzes the evolutionary characteristics of summer wet heatwaves at 382 urban meteorological stations in China during the period of 1970–2020. Results show that the frequency, duration, and intensity of summer wet heatwaves increased significantly in 83 % of the urban sites, with average growth rates of 0.016 times/year, 0.009 days/year, and 0.018 °C/year, respectively. South China experienced the fattest growth across China. Using the nearest rural site as a reference, the present research estimates that urbanization suppresses the trend of increasing summer wet heatwaves in 67 % of the urban stations. On average, urbanization reduces the frequency, duration, and intensity of wet heatwaves by 75.0 %, 55.5 %, and 38.9 %, respectively. The urban impacts on the frequency, duration, and intensity of wet heatwaves in Northeast China are approximately 9 %, 28 %, and 64 % of those observed in Central China, respectively. Additionally, the impact of urbanization on wet heatwaves extremes is primarily driven by changes in relative humidity. These findings underscore the widespread mitigating effect of urbanization on wet heatwaves, primarily through the UDI effect, and suggest that the urbanization effects on heatwave risk may be overstated if the UHI effect is considered in isolation.