西藏羊卓雍湖流域气候干湿状况分析

Analysis of climatic dry and wet conditions in Yamdok Tso Lake Basin of Tibet

应用Penman-Monteith模型分析了西藏羊卓雍湖流域潜在蒸散、干湿指数的年际变化趋势、年代际变化特征,并讨论了影响干湿指数变化的气象因子。结果表明:近46年(1961—2006年)羊卓雍湖流域年潜在蒸散以13.1mm.10a-1的速率显著减小,各季潜在蒸散均表现为减少趋势,减幅冬季最大,夏季最小;46年来羊卓雍湖流域季和年干湿指数的变化趋势均不明显,但近26年(1981—2006年)由于降水增加明显、潜在蒸散显著减小,除冬季外其他季节和年干湿指数都呈现明显的增大趋势,以夏季增幅最大;年平均干湿指数除20世纪80年代偏小外,其他年代均偏大,特别是90年代较为明显;干湿指数增大,暖湿化的气候变化趋势明显;降水量和相对湿度的明显增加,以及平均气温日较差的显著减小是干湿指数显著增加的主要原因,日照时数减少在干湿指数增加趋势中也起着重要作用。近年来,羊卓雍湖水位显现上升趋势,这可能与降水量增多和气温升高、冰雪融水增加有密切关系。

The 1961-2006 inter-annual and inter-decadal variations of potential evapotranspora- tion and dry-wet index in Yamdok Tso Lake Basin of Tibet were analyzed by Penman-Monteith model, with the meteorological factors affecting the variation of the dry-wet index identified. The results indicated that in 1961-2006, the annual potential evapotranspiration was decreased with a rate of 13.1 mm·10a-1. The seasonal potential evapotranspiration also had a decreasing trend, with the maximum in winter and the minimum in summer. Though the annual and seasonal varia- tions of the dry-wet index were not obvious, the dry-wet index itseff increased significantly in 1981-2006, both at the annual and the seasonal scales except in winter. The maximum increas- ing rate occurred in summer, which was attributed to the increased precipitation and decreased evapotransporation in this region in the recent 26 years. Except that in the 1980s, most of the av- erage annual dry-wet index was higher, with the maximum in the 1990s. The climate changed ^- ward an obvious warm-wet type, with dry-wet index increasing. The obviously increased dry-wet index could be mainly attributed to the obviously increased precipitation and temperature and the decreased mean daily range of temperature, together with the obviously declined sunshine hours which also played an important role in the dry-wet index. In recent years, the water level of the Yamdok Tso Lake ascended obviously, which was resulted from the increasing precipitation, tem- perature, and snow-melting.