西藏高原汛期降水日数和强度的时空演变特征

利用西藏高原38个气象站自建站以来至2007年的逐日降水资料,分析了西藏高原汛期不同等级降水日数和降水强度的时空演变特征及其对旱涝的影响。结果表明：西藏降水日数和小雨日数呈现北增南减的趋势,中雨日数在雅鲁藏布江中下游、昌都地区东南部一线增加。1961-2007年总降水日数的减少主要体现在小雨日数下降和贡献率减少,而中雨的日数和贡献率增加;降水强度表现出一定的增加趋势,体现为小雨和大雨强度的增加。20世纪80年代前多小雨,80年代至90年代多中雨以上强度的降水,21世纪前7年多小雨,而大雨主要在90年代对降水量的贡献率较大。西藏高原降水有向不均衡、极端化发展的趋势,这对西藏高原旱涝灾害的发生具有重要的影响。

Temporal and Spatial Variation of Precipitation Events Frequency and Intensity in Rainy Season during 1961-2007 in Tibet, China

Daily precipitation data collected in 38 weather stations in the Tibet plateau from 1961 to 2007 are used to analyze the spatial and temporal variation of precipitation events in rainy season, including the rain day in different grades and intensity, and its influence on drought and flood. The main conclusions are summarized as follows. The rain day and the light rain events increased in North Tibet and decreased in South Tibet, but the moderate rain events increased in the lower reaches of Yarlung Zangbo River to eastern Qamdo. The rain days in rainy season had a decreasing trend in recent 47 years, mostly due to the significant descent of light rain day and the decreasing of contribution of light rain to precipitation, but the moderate rain day and its contribution increased. The precipitation intensity showed an increasing trend due to the increasing of the intensity of light rain and heavy rain. The events of light rain were frequent before 1980s, the events of moderate and heavy were frequent during 1980-2000, the events of light rain were frequent during 2001-2007. The contributions of heavy rain had an obviously positive trend in 1990s. The extremity brought drought and flood which were likely to become severe due to the change trend.