1967—2008年青藏高原汛期不同强度降水日数变化

利用1967—2008年青藏高原68个台站逐日降水资料,按照《气象规范》对不同等级降水的定义,对青藏高原汛期（5—9月）不同强度的降水日数进行分析。结果表明：1967—2008年青藏高原汛期总降水日数及各强度降水日数均呈现出由东南向西北递减的空间分布特征,降水总日数和小雨日数以减少趋势为主,最显著的区域位于青藏高原东北和东南部,中雨日数以增加为主,大雨日数变化趋势的区域差异显著。青藏高原汛期各强度降水日数存在明显的年际变化,总降水日数的变化主要受小雨日数影响。汛期降水各旬分布上,各强度降水日数主要集中在夏季（6—8月）,小雨日数越少（多）的旬内其占总降水日数的比例就越大（小）,中雨和大雨日数越少（多）的旬内占总降水日数的比例就越小（大）;小雨和中雨日数均在1978年发生突变,突变前后,青藏高原东南部小雨和中雨日数差异最为明显。

Variation of precipitation days under different intensity in the flood season from 1967 to 2008 over the Tibetan Plateau

Based on the daily precipitation data in 68 weather stations from 1967 to 2008 over the Tibetan Plateau and the definition of precipitation of different intensity from the meteorological criterion,a number of precipitation days under the different intensity in the flood season from May to September were analyzed.The results indicate that the number of days of the total precipitation and the different intensity have the decreasing trends from the southeast to the northwest in the Tibetan Plateau.The number of days of the total precipitation and light rain decrease in the Tibetan Plateau,especially in the northeast and the southeast of the Tibetan Plateau.Days with moderate rain increase in the Tibetan Plateau,while days with heavy rain are different in different regions.There is a significant inter-annual change for precipitation days of different intensity in the flood season.The variation of the total precipitation days is influenced by that of days with light rain.For precipitation distributions in a period of ten days in the flood season,a number of days with different intensity precipitation mainly concentrate in the summer from June to August.The fewer days with light rain are in a period of ten days,the larger its ratios to days with the total precipitation are,and vice versa.However,the fewer days with moderate rain and heavy rain are in a period of ten days,the smaller its ratios to days with the total precipitation are,and vice versa.The abrupt changes of days with light rain and moderate rain both occur in 1978,and the difference between days with light rain and moderate rain is obvious in the southeast of the Tibetan Plateau around year 1978.