天山西部地区近50年干旱指数的演变特征

利用天山西部地区9个县市气象站近50年的降水、气温和水面蒸发观测资料，确定适合该区的干旱指数计算方法，分析了该区干旱指数的主要特征和演变趋势。结果表明，按行政分区和流域分区两种方法统计，研究区的气候类型为半湿润—半干旱区，其年干旱指数具有明显的地区分布特性和年际变化。近50年来，各行政分区和流域分区各分级年干旱指数发生的频次及频率也不尽相同，半湿润区湿润化程度较高，而半干旱区的年度和夏季的干旱化程度高，春、秋两季干湿化程度则基本相近。研究区50年以来的平均年干旱指数总体呈下降趋势，尤以夏季干旱指数的下降趋势明显，可以初步认为，水面蒸发量的显著减少是主要影响因素之一。

Special Characteristics and Long-term Trend of Aridity Index in the West part of the Tianshan Mountains during Last 50 years

Based on the precipitation and evaporation data observed by meteorological stations of 9 counties in the west part of the Tianshan Mountains during recent 50 years, the spatial distribution and temporal trend of aridity index values are analyzed by the calculation method. The results show that, this region can be classified into semi-arid-semi-humid climatic zone by two different calculation specifications. Within the region, values of annual aridity index have remarkable regional difference and high interannual variation. Besides, frequency for five classes of aridity index occurred in different administrative division or sub-region, are calculated obviously different. And values of annual aridity index decrease respectively during last 50 years, especially the summer values. Significant reduction of evaporation from water surface is found to be the major influence factor.