Changes in precipitation extremes in the Beijing metropolitan area during 1960-2012

In this study, we use several methods including the minimum cross entropy, wavelet transform coherence method, and the Mann-Kendall test to study the changes in the frequency of precipitation extremes and their contributions to total precipitation at different extreme percentile thresholds (90th percentile, 95th percentile, and 99th percentile) in the Beijing metropolitan area. Overall, the spatial distribution of the extreme precipitation thresholds is consistent with that of total precipitation, with the highest distribution appearing in the northeast part of the study area and the lowest distribution appearing in the west. The extreme precipitation events with high-percentile thresholds have more spatial and temporal variability than those at the low-percentile thresholds. We consider two types of indices representing frequency of extremes and their contributions to total precipitation. The frequency indices show similar spatial and temporal trends relative to the total precipitation than the contribution ratio indices. Additionally, the possible impacts of global climate indices, urban expansion and topography on the change in precipitation extremes are also considered. The weakening Eastern Asian monsoon (EAM) since 1970s has significantly influenced the change in contribution from indices of extreme precipitation over Beijing. The changes in precipitation extremes are also influenced by rapid urban expansion and topography, especially in spatial changes, with the higher values appearing in the urban and plain areas. In the context of global climate change and rapid urbanization, greater challenges in urban flooding and safety are caused by the changes in precipitation extremes.