Urban signatures in the spatial clustering of precipitation extremes over mainland China

Urban areas demonstrate great influence on precipitation, yet the spatial clustering features of precipitation is still unclear over urban areas. This study quantitatively examines the spatial clustering of precipitation intensity in 130 urban-affected regions over mainland China during 2008-2015 using a high-resolution merged precipitation product. Results show that the spatial heterogeneity patterns display diverse distribution and vary with precipitation intensity and urban sizes. Extreme and heavy precipitation has higher spatial heterogeneity than light precipitation over the urban-affected regions of grade 1 cities, and their mean Moran’s I are 0.49, 0.47 and 0.37 for the intensity percentiles of ≥95%, 75-95% and <75%, respectively. The urban signatures in the spatial clustering of precipitation extremes are observed in 37 cities (28%), mainly occurring in the Haihe River Basin, the Yangtze River Basin and the Pearl River Basin. The spatial clustering patterns of precipitation extremes are affected by the local dominant synoptic conditions, such as the heavy storms of convective precipitation in Beijing (Moran’s I =0.47) and the cold frontal system in the Pearl River Delta (Moran’s I =0.78), resulting in large regional variability. The role of urban environments for the spatial clustering is more evident in wetter conditions (e.g., RH >75% over Beijing and RH >85% over the Pearl River Delta) and warmer conditions (T >25°C over Beijing and T >28°C over the Pearl River Delta). This study highlights the urban modification on the spatial clustering of some precipitation extremes, and calls for precautions and adaptation strategies to mitigate the adverse effect of the highly clustered extreme rainfall events.