Study of the temporal and spatial patterns of drought in the Yellow River basin based on SPEI

Drought is one of the severe natural disasters to impact human society and occurs widely and frequently in China, causing considerable damage to the living environment of humans. The Yellow River basin (YRB) of China shows great vulnerability to drought in the major basins; thus, drought monitoring in the YRB is particularly important. Based on monthly data of 124 meteorological stations from 1961 to 2015, the Standardized Precipitation Evapotranspiration Index (SPEI) was used to explore the temporal and spatial patterns of drought in the YRB. The periods and trends of drought were identified by Extreme-point Symmetric Mode Decomposition (ESMD), and the research stages were determined by Bernaola-Galvan Segmentation Algorithm (BGSA). The annual and seasonal variation, frequency and intensity of drought were studied in the YRB. The results indicated that (1) for the past 55 years, the drought in the YRB has increased significantly with a tendency rate of ?0.148 (10 a)^?1, in which the area Lanzhou to Hekou was the most vulnerable affected (?0.214 (10 a)^?1); (2) the drought periods (2.9, 5, 10.2 and 18.3 years) and stages (1961–1996, 1997–2002 and 2003–2015) were characterized and detected by ESMD and BGSA; (3) the sequence of drought frequency was summer, spring, autumn and winter with mean values of 71.0%, 47.2%, 10.2% and 6.9%, respectively; and (4) the sequence of drought intensity was summer, spring, winter and autumn with mean values of 0.93, 0.40, 0.05 and 0.04, respectively.