资源环境科技发展态势分析平台

The arid/semiarid region of Northwest China (NWC, north to 35 degrees N, and west to 100 degrees E in China) experienced significant wetting after the late 1980s. We used both the summer precipitation and standardized precipitation indices (precipitation index [PI] and standardized precipitation index) to reexamine the regime shift. Consistent with the rainfall, the drought condition represented by the standardized precipitation index was significantly alleviated over most areas of NWC during P2 (1989-2016) than that during P1 (1961-1988). Along with the increased rainfall over the NWC, significant changes also occur in the interannual variation-related circulation. The Ural High (UH) was found to be closely related with the interdecadal change during the late 1980s. The NWC PI-related wave propagation from the UH weakened after the late 1980s. The persistent tropical Indian Ocean sea surface temperature (SST) from the preceding winter to the summer were also found to influence the NWC PI through modulating the South Asian High during P1. However, during P2, the ENSO signals in the preceding winter, which can be memorized by the Indian Ocean SST in the spring and propagate to the Indo-Pacific SST in the summer, can influence the NWC PI. The wave train pattern in the convection from the Maritime Continent to NWC and northwestern Europe seems to be a key bridge. The UH seems to be independent of the above SST-forced atmospheric circulations. The SST signals of the preceding winter can provide useful information for the summer drought prediction in NWC.