An Abrupt Rainfall Decrease over the Asian Inland Plateau Region around 1999 and the Possible Underlying Mechanism

A decadal change in summer rainfall in the Asian inland plateau（AIP） region is identified around 1999. This decadal change is characterized by an abrupt decrease in summer rainfall of about 15.7% of the climatological average amount,leading to prolonged drought in the Asian inland plateau region. Both the surface air temperature and potential evapotranspiration in the AIP show a significant increase, while the soil moisture exhibits a decrease, after the late 1990s. Furthermore,the normalized difference vegetation index shows an apparent decreasing trend during 1999–2007. Three different drought indices—the standardized precipitation index, the standardized precipitation evapotranspiration index, and the self-calibrating Palmer drought severity index—present pronounced climate anomalies during 1999–2007, indicating dramatic drought exacerbation in the region after the late 1990s. This decadal change in the summer rainfall may be attributable to a wave-like teleconnection pattern from Western Europe to Asia. A set of model sensitivity experiments suggests that the summer warming sea surface temperature in the North Atlantic could induce this teleconnection pattern over Eurasia, resulting in recent drought in the AIP region.

我国东部夏季三类雨型的诊断和预测方法研究

采用三级逐步判别方法对我国东部地区夏季（６、７、８月）降水进行客观诊断和预测。结果表明，利用６个测站的夏季降水量即可定量诊断我国夏季雨型，利用冬季５００ｈＰａ极涡面积和北半球遥相关型指数建立起来的三级判别函数只包含７个因子。历史拟合率为３８／３９，试报效果也较好，从而为我国东部地区夏季降水型的客观预报提供了有应用价值的预报模型。