西北地区降水特征及变化规律分析

Analysis on characteristics and change patterns of precipitation in northwest China

根据我国西北地区降水气候特征研究状况，利用较具代表性的我国西北地区北亚热带、温带驻防的25个空军机场气象台站1970-2000年历年逐时降水资料，从降水量、降水强度、降水时间、降水频率等方面，以气候区划区为区域分析单位，分析了西北地区的降水变化规律和特征。结果表明：西北地区北亚热带、温带年际降水量有从东南和西北两侧向中部明显减少的分布格局。30a间中温带干旱区东部及其以东地区的降水量呈下降趋势，以西则基本呈上升趋势。降水强度基本表现为上升趋势，强度呈东南大、西北小分布，且以北亚热带湿润区和南温带干旱区南疆区上升速率表现最大。降水时间呈现减少趋势，其分布特点与降水量分布基本上一致，由东南和西北两侧向中间明显减少。近30a来降水量东降西升，降水小时数、降水频率呈下降趋势，但小时雨强和中雨以上强度降水比重一直呈上升趋势，降水以短时、量大为特征出现的机率在增加，降水的有效利用难度在加剧，这种特征东部比西部要明显得多。青藏高原东侧降水量和降水小时数都处于下降趋势，雨强呈上升趋势，该地区干旱趋势在加剧。但在高原东北侧、北侧这种趋势表现相对要弱一些。

According to the climatic conditions of precipitation in northwest China, by making use of the precipitation data of 25 meteorological stations during 1970-2000 in the north subtropical and temperate zone of northwest China, this paper analyzed the characteristics and change patterns of the precipitation from the aspects of the amount, intensity, time and frequency of precipitation. The results show that, during 1970-2000, there was a tendency of decrease of precipitation from both southeast and northwest sides to the central region in the north subtropical and temperate zone in northwestern China. In the east part of middle temperate zone, the precipitation tended to decrease, but in the west part, it tended to increase. The precipitation intensity generally tended to ascend, the ascending range being largerin the southeast region than in the northwest region, and the ascending rate was the largest in southern Xinjiang where was located in the north subtropical humid zone and the south temperate arid zone. The precipitation time showed a trend of reducing, and its distribution characteristic was basically identical to the amount of precipitation, i.e., being decreased from both southeast and north- west sides to the central region. During 1970-2000, the precipitation amount was increased in the west part but decreased in the east part, and the precipitation time and frequency showed a decreasing tendency, whereas the precipitation intensity and the prolzortion of strong rain showed an ascending tendency, indicating that the probability of shortterm and strong rainfall was increasing and the difficulty in effective use of rainfall was intensified, especially in the east part. Both the amount and time of precipitation in the east part of Qingzang Plateau tended to decrease, showing that the tendency of drying was intensified in this region. However, this characteristic was less obvious in the northeast and north part of the plateau.