A universal multifractal approach to assessment of spatiotemporal extreme precipitation over the Loess Plateau of China

摘要

Extreme precipitation?(EP) is a major external agent driving various natural hazards in the Loess Plateau?(LP), China. However, the characteristics of the spatiotemporal?EP responsible for such hazardous situations remain poorly understood. We integrate universal multifractals with a segmentation algorithm to characterize a physically meaningful threshold for EP?(EPT). Using daily data from?1961 to?2015, we investigate the spatiotemporal variation of?EP over the?LP. Our results indicate that (with precipitation increasing) EPTs range from 17.3?to 50.3 mm d?1, while the mean annual?EP increases from 35?to 138 mm from the northwestern to the southeastern?LP. Further, historically, the EP?frequency?(EPF) has spatially varied from 54 to 116 d, with the highest EPF occurring in the mid-southern and southeastern?LP where precipitation is much more abundant. However, EP?intensities tend to be strongest in the central?LP, where precipitation also tends to be scarce, and get progressively weaker as we move towards the margins (similarly to EP?severity). An examination of atmospheric circulation patterns indicates that the central?LP is the inland boundary with respect to the reach and impact of tropical cyclones in China, resulting in the highest?EP intensities and EP?severities being observed in this area. Under the control of the East Asian monsoon, precipitation from June to September accounts for 72 % of the total amount, and 91 % of the total?EP events are concentrated between June and August. Further, EP?events occur, on average, 11 d earlier than the wettest part of the season. These phenomena are responsible for the most serious natural hazards in the?LP, especially in the central LP region. Spatiotemporally, 91.4 % of the LP?has experienced a downward trend in precipitation, whereas 62.1 % of the area has experienced upward trends in the EP?indices, indicating the potential risk of more serious hazardous situations. The universal multifractal approach considers the physical processes and probability distribution of precipitation, thereby providing a formal framework for spatiotemporal EP assessment at the regional scale.