中国水面蒸发量的变化

采用600余个台站资料,对全国及主要流域蒸发皿记录的蒸发量及相关气候要素变化趋势进行了分析。1956-2000年期间,我国水面蒸发量呈显著下降趋势,东部、南部和西北地区下降更多。我国长江、海河、淮河、珠江以及西北诸河流域的年平均水面蒸发量均明显减少,海河和淮河流域减少尤为显著,黄河和辽河流域减少也较明显,但松花江和西南诸河流域未见明显变化。长江、淮河流域夏季减少速率最大,珠江、辽河以春季减少为主,海河、西北诸河流域春、夏两季都显著减少,黄河、东南诸河、西南诸河等流域四季均有轻度减少,松花江流域四季变化趋势都不明显。全国多数地区日照时数、平均风速和温度日较差同水面蒸发量具有显著的正相关性,并与水面蒸发呈同步减少,为引起大范围蒸发量趋向减少的直接气候因子;地表气温和相对湿度一般在蒸发减少不很显著的地区与蒸发量具有较好的相关性,绝大部分地区气温显著上升,相对湿度稳定或微弱下降,表明其对水面蒸发量趋势变化的影响是次要的。

Change in Pan Evaporation and the Influential Factors over China:1956-2000

Trend of pan evaporation and the related climate factors for the entire country and ten discharge basins of China are analyzed using a data set of total 600 stations.A significant decreasing trend in pan evaporation for the country as a whole has been found for the period from 1956 to 2000,with eastern,southern and northwestern China experiencing the most marked decrease.Eight of the ten discharge basins are found to be weaker in evaporating presently as compared to 1950's and 1960's,while two of them,the Songhuajiang Basin and the rivers of southwestern China,witnessed no significant change.The most significant decline occurred in the Yangtze River,Haihe River,Huaihe River,Zhujiang River,and northwestern rivers basins.The decrease is most obvious in summertime in the Yangtze and Huaihe rivers,in springtime in the Zhujiang and Liaohe rivers,and in both summertime and springtime in the Haihe River and northwestern rivers.The Yellow River,southeastern rivers and southwestern rivers are characterized by a decrease with no season being dominant,and the Songhuajiang River has no season when pan evaporation decreased significantly.In most parts of the country,a significant positive correlation of pan evaporation with sunshine duration,average wind speed and daily temperature range can be found.With the change of pan evaporation,these variables also experienced an evident negative change,indicating that they might have played an important role in the change of pan evaporation.It is more uncertain for air temperature and relative humidity,which show a good relationship with pan evaporation only in areas where no significant decrease occurred,indicating that they are generally not the main climate factors affecting pan evaporation.Possible causes for the evident decrease of sunshine duration and mechanisms for the climate factors to affect pan evaporation are also discussed in the paper.