Abstract:
The persistent droughts during the last two decades in North China are studied.The main results are as follows :(1) The Palmer Drought Severity Index (PDSI) shows that there is inter-annual variation in droughts in North China.The inter-decadal variation is even more remarkable.Before the mid-1970s, there was wetsummer climate, while since 1970, there were more drought years in North China.Moreover, the most severe droughts happened after the 1980s.(2) Summer droughts in North China are the consequence of persistent anomalous circulation over the Eurasia.The main features of the anomalous circulation include that there is height anomaly in the region of 55°to 65°N, 60°to 135°E and that there was EU teleconnection and it is the main type of atmospheric circulation anomalies that causes the persistent summer droughts in North China.(3) During the summer drought years, there is continuity in the distribution of the 500 hPa height anomaly field from winter to summer.(4) The anomalies of the general atmospheric circulation during droughts in North China are not local phenomena, but the responses to the Northern Hemisphere general atmospheric circulation anomaly.