长江上游区域蒸发皿蒸发量变化及其对水分循环的影响

利用长江上游最近30年(66个测站)蒸发皿蒸发量和最近50年(90个测站)的7种气象要素,分析了蒸发皿蒸发量的区域变化趋势和影响蒸发皿蒸发量变化的因素;针对7个水文站的年径流量变化,探讨了蒸发皿蒸发量变化后对水分循环的影响.结果表明,长江上游蒸发皿蒸发量的变化可以划分为三个分区,研究区域东西两侧(青藏高原和大巴山一带)为显著减少区,分别命名为RⅠ和RⅡ,中间(云贵高原北部到黄土高原南缘以及由二者包围的四川盆地一带)为显著增大区,命名为RⅢ区.影响区域蒸发皿蒸发量变化的原因各有不同,青藏高原一带(RⅠ区)蒸发皿蒸发量减少的原因可归结于太阳辐射强度和风动力扰动减弱所致.大巴山一带(RⅡ区)减少原因是太阳辐射强度、风动力扰动强度、湿度条件都在显著下降所引起的.云贵高原到四川盆地一带(RⅢ区)蒸发皿蒸发量增加是环境气温强烈升高,导致其上空大气水汽含量显著减少,大气很干燥,引发蒸发过程加强所致.蒸发皿蒸发量发生变化的直接后果就是导致水分循环强弱发生变化,对于RⅠ区,尽管蒸发皿蒸发量减少,由于降水量和径流量增加的作用,这一区域的水分循环有所加强.在RⅡ区,降水量、径流量和蒸发量都在减少,因此RⅡ区水分循环显著减弱.在RⅢ区,降水量和径流量同时减少,而蒸发量增大,水量消耗增大,因此RⅢ区水分循环有减弱趋势.

Pan evaporation change and its impact on water cycle over the upper reach of the Yangtze River

On the basis of pan evaporation measurement (1980—2008, 66 meteorological sites) and seven meteorological elements (1961—2005, 90 meteorological sites) for the upper reach of the Yangtze River, the pan evaporation region change characteristics and its causes were analyzed. Where the annual runoff changes of seven hydrological sites were concerned, the impacts of the pan evaporation change on water cycle were investigated. The results show that according to the characteristics of pan evaporation, the upper reach of the Yangtze River could be divided into three different climate regions. The eastern and western regions in the reach are all the statistically significant decrease regions, such as the Qinghai-Tibetan Plateau and Daba Mountain, which are named as RⅠ and RⅡ, respectively. The middle region is the significant increase one, like the Sichuan Basin, named as RⅢ. There are different meteorological elements that resulted in the changes of pan evaporation for those three regions. The decrease of pan evaporation in the region RⅠ owed to the reduction of solar irradiance and wind speed disturbance. In the region RⅡ the decrease of pan evaporation was caused by the significant reductions of multi-meteorological elements, including solar irradiance, wind speed disturbance, near surface and atmospheric humidity. For the region RⅢ, the air temperature significantly increased and then the air near the surface and whole atmosphere became dry, which resulted in the increase of pan evaporation in this region. The pan evaporation change directly influenced the water cycle in the survey reach. The water cycle in RⅠ intensified due to the increases of rainfall and surface runoff, despite pan evaporation decreasing. In RⅡ there were the decreases of three elements, such as rainfall, runoff and evaporation, so that the water cycle in this region weakened significantly. For RⅢ, the water cycle weakened due to decreasing rainfall and runoff as well as increasing pan evaporation.