Investigating the effects of precipitation on drought in the Hanjiang River Basin using SPI

The Hanjiang River Basin serves as the water source for the Middle Route South-to-North Water Delivery Project. Droughts are not uncommon in this region and have affected the water supply directly. This study is designed to gain more in-depth knowledge of spatial and temporal drought variations in the Hanjiang River Basin, and the synchronization of drought variations in upstream and downstream regions of the Danjiangkou Dam. Compared with drought analysis in the upstream or the downstream, respectively, research shows the spatial difference between the upstream and the downstream clearly. The following conclusions can be drawn: Standardized Precipitation Indexes in the Hanjiang River Basin did not significantly decrease; droughts considered moderate or worse occurred most frequently in autumn and winter, but most rarely in summer; the cumulative probability of moderate to severe droughts was highest in October and December. Drought conditions in the upstream region varied in a fluctuating way. The upstream region has become increasingly wet since the turn of the 21st century, while the downstream region has become increasingly dry since the 1990s. The probability of synchronous droughts both upstream and downstream was only 9.8%.