采用MannK-endall非参数检验方法和反距离权重插值法IDW对长江流域近40年来20cm蒸发皿蒸发量及其影响因素进行了时空变化趋势分析,研究结果表明:近40年来,长江流域年平均蒸发皿蒸发量在全流域和不同区域内均呈现显著的下降趋势,且中下游地区(99%的置信度)比上游地区(95%的置信度)下降趋势显著,夏季(99%的置信度)比其它季节下降趋势显著。影响蒸发皿蒸发量的主要气象因子太阳净辐射和风速呈现显著下降趋势,气温表现为显著升高趋势,但中下游地区夏季温度微弱下降,降水微弱增加,但中下游地区夏季降水显著增加。因此,长江流域年平均太阳净辐射和风速的显著下降是年平均蒸发皿蒸发量显著下降的主要原因,而中下游地区夏季气温的微弱下降和降水的显著增加使得中下游地区夏季蒸发皿蒸发量下降趋势尤其显著。

Applying Mann-Kendall trend test and IDW interpolation methods,trends of 20cm pan evaporation and its impact factors over the Yangtze River Basin were analyzed from 1961 to 2000.Significant negative trend of pan evaporation was detected in the upper,middle and lower reaches as well as the whole basin,but this trend is more significant in the middle and lower reaches(99% confidence level) than that in the upper reaches(95% confidence level),and more significant in summer(99% confidence level) than that in other seasons.Significant negative trends of annual mean solar net radiation and wind speed were found over the Yangtze River Basin.Significant positive trend of annual mean air temperature was detected,while slight decreasing trend of summer air temperature was observed in the middle and lower reaches.Slight increasing trend of annual mean precipitation was detected over the Yangtze River Basin,but significant increasing trend of summer precipitation was found in the middle and lower reaches.Therefore,the significant negative trends in solar net radiation and wind speed over the basin cause the decrease in pan evaporation after compensating the increase in air temperature,and the significant increasing of summer precipitation and slight decreasing of summer air temperature in the middle and lower reaches enhanced the confidence level of the decreasing trend of summer pan evaporation.