近50 a中国西北地区东部降水特征

利用我国西北地区东部54个气象站1960-2009年的降水资料，采用M-K检验和小波分析方法，对该地区的降水特征进行了分析。结果表明：① 西北地区东部降水量呈微弱下降趋势，1990年后降水减少趋势更为明显，Ⅱ区降水变化趋势较Ⅰ区更加显著；② 该地区降水频次以弱降水和中等强度降水为主，占降水总天数的70%以上，弱降水频次减少趋势显著；③ 中等强度降水和强降水的降水量占全年降水的75%以上，中等降水的降水量呈减少趋势，是造成年降水量减少的主要原因；④ 小波分析结果显示，年降水、中等降水和强降水序列均存在显著的3 a和5 a短周期，其中Ⅰ区和Ⅱ区的中等降水和强降水小波周期在20世纪70年代之后完全不同，中等降水的减少与70年代周期的变长密切相关。

Precipitation in the Eastern Part of Northwest China in Recent 50 Years

Based on the precipitation data observed by 54 meteorological stations in the eastern part of northwest China during the period of 1960-2009, the variation of precipitation in this region was analyzed using the Mann-Kendall test and wavelet analysis. The main results were as follows: (1) Precipitation in the study area was in a slight decrease trend, the precipitation reduction was more obvious after 1990, and the variation of precipitation in area Ⅱwas more significant than that in area I; (2) The precipitation frequency in the study area was dominated by weak and moderate precipitation events, which accounted about 70% of the total precipitation days, and the decrease of weak precipitation frequency was obvious; (3) The proportion of moderate and heavy precipitation accounted for more than 75% of annual precipitation. Decrease of annual precipitation was mainly caused by the decrease of moderate precipitation; (4) The results of wavelet analysis revealed that there were the 3 year and 5 year fluctuation periodicities of annual, moderate and heavy precipitation, the periodicities of moderate and heavy precipitation in area I were completely different from those in area Ⅱafter the 1970s, and the decrease of moderate precipitation was closely related to the variation of moderate precipitation in the 1970s.