青藏高原强降水日数的时空分布特征

 根据青海和西藏48个气象台站近48 a（1961-2008年）的逐日降水和气温资料，分别以日降水量超过5 mm和25 mm作为冬半年（11月～翌年3月）和夏半年（5～9月）强降水的临界值，分析了青藏高原冬、夏半年强降水日数的时空分布特征。结果表明：（1）高原强降水日数与总降水量的空间分布型非常相似，夏半年均表现为由东南向西北递减，而冬半年则为由高原腹地向四周递减。（2）夏（冬）半年强降水主要集中在7月上旬～8月中旬（11月上旬和3月中下旬）。（3）夏（冬）半年强降水存在准6 a（5～6 a）的年际振荡以及准10～11 a（15 a）的年代际振荡。（4）强降水日数变化趋势的空间差异较大，夏半年高原北（南）部强降水日数普遍以增加（减少）趋势为主，而冬半年除雅鲁藏布江流域呈减少趋势外，高原大多数地区均表现出显著增加趋势。

Temporal and spatial distribution of strong precipitation days over the Tibetan Plateau

By using of the daily precipitation and temperature data of 48 stations from 1961 to 2008 in Qinghai and Tibet,the spatial and temporal characteristics of strong precipitation days during the winter(November to next March) and the summer half year(May to September) over the Tibetan Plateau are discussed by means of linear trend analysis,Morlet wavelet and Mann-Kendall analysis etc statistical analysis methods.Through the contrastive analysis of the precipitation characteristics over the plateau and plain area with latitude,more than 5 mm of daily snowfall and 25 mm of daily precipitation are used as the critical values of heavy precipitation during the winter and summer half year respectively according to the actual situation of precipitation over the plateau.The results show that probabilities of heavy rainfall resulting are lager in the areas which have more rainfall.The spatial distribution of heavy rainfall days is very similar to total rain over the Plateau,which decreases from southeast to northwest during the summer half year,while declines from the center of the Plateau to the surrounding during the winter half year.In the southeast of the Plateau,although the snow days and snow is few,the heavy rainfall days account for a higher proportion of the total snowfall days.Heavy precipitation is mainly concentrated in early July to mid-August(early November to mid-late March) during the summer(winter) half year.Heavy rainfall days in mid-June increased slowly,and in late July they are the most,then,after mid-August reduce rapidly.Additionally,the heavy precipitation during the summer(winter) half year has obvious interannual oscillation with quasi-six years(5-6 years) and inter-decadal oscillation with quasi-10-11-year(quasi-15-year).During the summer half year,the space variation tendency of heavy rainfall days is uneven.It mainly increases(decreases) in the northeast(southeast) of Qinghai and in the west(east) of Tibet.During the winter half year in addition to the Yarlung Zangbo River and individual regions show decreasing trends,most parts of the Plateau are significantly increased.In the recent 48 years,heavy rainfall days show weak downward trend,while weak rainfall days show upward trend during the summer half year.Because of that the rise tendency of heavy snowfall(days) is much stronger than weak snowfall(days),the rise tendency of snowfall is mainly affected by heavy snowfall during the winter half year over the Plateau.