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

Abstract

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.