中天山及其北麓的降水变化及其原因分析

Precipitation over the Middle Tianshan Mountains and Their Northern Slopes: Variations and Their Cause

利用中天山地带85.0°～90.0°E,42.5°～45.0°N范围内17个气象站1961—2000年的降水、气温观测数据及美国NCEP/NCAR1950—2000年再分析月平均资料进行计算和分析,结果表明:这一区域近年来降水呈现上升趋势,且冬、夏季相对显著,山区降水增幅大于山前平原地带.年代际变化表现为60—70年代降水量减少,80—90年代逐步增加.大气可降水量多年也表现为增加趋势.近50a来该地区上空的水汽输送状况显示,年平均大气水汽输入为9217.8×108m3,输出水汽8625.7×108m3,净收支为592.0×108m3,且水汽收支主要取决于夏半年的水汽输入量,境外全年输入的水汽只有6.4%转化为降水.从50—90年代水汽净收支总体上呈减少趋势,只在90年代有略微增长.结合该地区的河流径流增加、冰川物质平衡一直处于亏损状态,说明中天山北麓近年来降水量增加的主要原因是由于该地区内部的水循环量增加和水循环速率提高.

The changes of water resources and the reasons which cause the changes over the middle Tianshan Mountains between 42 ^5 N and 45 ^0 N,and 85 ^0°E and 90 ^0°E were analyzed by using observed data of 17 meteorological stations during the past 40 years and monthly mean data provided by NCEP/NCAR from 1950 to 2000. In this area the annual mean precipitation was gradually going up and increasing obviously in summer and winter. At the same time, the increase in annual mean precipitation of mountain areas was more than that of the surrounding plains. Mean decadal precipitation of 17 stations came down form the 1960s to the 1970s, but went up from the 1980s to the 1990s. Moreover, the precipitable water showed an increasing trend. In the atmosphere over the area of 2 ^5×5 ^0 , the annual influent water vapor amount was {9 217.8 }×10 8 m 3 , the annual effluent water vapor amount was {8 625.7 }×10 8 m 3 , and annual net water vapor amount was 592 ^0×10 8 m 3 , averaged over the past 50 years. The influent water vapor amount in summer mainly contributes to annual net water vapor amount. Only 6 ^4% of annual influent water vapor amount contributed to precipitation, which was lower than that of the China mainland. The water budget was inclined to reduce from the 1950s to the 1990s but slightly increased in the 1990s. Considering runoff goes up and glaciers retreat, it is thought that one reason to cause the rainfall increasing over the middle Tianshan Mountains is the increase of the locally circulatory water amount and the locally circulatory frequency.