Abstract: Using a regional climate model (RegCM3) nested in oneway mode within the Community Climate System Model (CCSM3), some high resolution numerical experiments were conducted under the SRES A2, A1B and B1 scenarios for the 21st century, and the drought characteristics and their possible trends in the Sino-Mongolian arid and semiarid regions were analyzed. The results show that the precipitation and surface temperature have an obvious increasing trend under all scenarios. There is no clear drying trend in the 21st century based on the analyzed results of precipitation. Considering from the Palmer Drought Severity Index (PDSI), however, the signals of precipitation and temperature reveal that the drought area may be expanded continuously. The proportions of extremely severe, severe and moderate drought areas are increased, which are all significant at significance level of 95%. The extremely severe drought area was expanded by higher than 3% under all the scenarios in the late-21st century compared with that in the mid-21st century. Compared with mid-21st century and modern time, the drought areas will be enlarged by 8% and 11.51% under A2, 12.48% and 18.34% under A1B, and 9.73% and 10.82% under B1 in the late-21st century, respectively. The change of both precipitation and temperature must be taken into account in predicting climate change in arid and semiarid regions so as to more accurately reflect the characteristics of drought and drying trend.  

Key words: global warming, drought trend, Palmer Drought Severe Index, RegCM3, arid and semiarid regions, Sino-Mongolian