The evolution analysis of seasonal drought in the upper and middle reaches of Huai River basin based on two different types of drought index

The Huai River Basin is in the transitional zone between the climates of northern and southern China, and is liable to seasonal drought. This study is based on two types of drought index, one is the traditional meteorological drought index including precipitation anomaly percentage (P-a) and Standardized Precipitation Index (SPI), and the other is the remote sensing drought index (water deficit index, WDI), analyzing the serious winter and spring drought development and evolution of the Huai River Basin. The results showed that: (1) the drought development was similar based on P-a and SPI, but the indicated drought intensity was different, SPI was closer to the actual drought degree. (2) WDI reflect drought and spatiotemporal characteristics well, and respond quickly to soil wet conditions caused by short-term rainfall. (3) WDI had significant correlation with P-a and SPI, and the correlation coefficients were 0.93 and 0.92, respectively, which means WDI can supplement meteorological drought index, but WDI is better than meteorological drought index on the whole, which is helpful to improve the ability of assessing regional drought.