祖厉河流域近50a降水变化及典型人类活动对降水的影响

Rainfall Variation in Zuli River Basin in the Past 50 Years and Influnence of Typical Human Activities

对祖厉河流域近50a降水资料的分析结果表明：祖厉河主流域区等降水量线纬向分布特征明显，降水量随纬度增高而减少；在流域南部和东北部高度差大的地方，降水量随高度增高而增加；受地形影响，祖厉河中下游有一条干舌自西北向东南伸到流域东部边缘，与周边区域相比，干舌区降水偏少90～140mm。近50a祖厉河流域降水显著减少，区域平均减少106．4mm。小波分析表明，25a以上和10a左右的降水变化周期很明显，目前处于偏少期；区域平均降水量从20世纪60年代后期开始减少，1986年发生了突变，之后迅速减少。流域内降水季节分配很不均匀，夏季降水最多，占年降水的55％，春、秋季均占年降水的21％，冬季占年降水的3％；春、夏季降水减少不显著，秋季降水减少显著，但进入本世纪，秋雨开始增多，冬季降水有不显著的增多趋势。中下游过度垦殖及河流源头过多的小水利工程等人类活动造成地表状况变化，降水有加剧减少的迹象；流域外大量调水虽然对降水不足有相当的补偿作用，但地表调水显然没有使流域内的天然降水量增加；地表植被增加和人类活动对地表影响较小的区域降水减少比较缓慢。

The analysis on rainfall along the Zuli River valley in the past 50 years shows that rainfall decreased with latitude but increased with altitude in the northeast and southern areas where the altitude varies suddenly. The rainfall was 90 - 140 mm less in an area which shape likes a tougue extending from northwest to southeast till the east edge in the middle and lower area of Zuli River compared with other areas. In the past 50 years, the regional rainfall in Zuli River basin decreased 106.4 mm on average. Wavelet analysis shows that more than 25 years and about 10 years periods in rainfall change are remarkable. The regional mean rainfall decreased from the late 1960s, and in 1986 it increased but after that it decreased much quickly. On the other hand, the seasonal rainfall distribution there was different, and it was the most in summer, less in spring and autumn and the least in winter with 55% , 21% and 3% of annual rainfall, respectively. The rainfall in autumn decreased much more in the past 50 years, but it tends to increase in the beginning of this century. Influenced by human activities, rainfall there presented accelerating decrease trend because of excessive cultivation in the middle and lower region and many small water conservancies in the upper of the river. The rainfall decreased slowly where vegetation cover increased and human activities influenced less on land surface.