Researches Of Secular Variation Features And Possible Influence Factors Of Precipitation In Northwest China

The 1951-2002 daily precipitation data of 131 stations in northwest China are used to conduct an overall researches of the climatic variation features of precipitation in northwest China and an analysis of the distribution type of general circulation and sea temperature that influence precipitation of rainfall season in northwest China. Results show:(1) The annual precipitation in northwest China increases rapidly from northwest to southeast, the relative variability of precipitation in rain spell is smaller than that in dry region. The tendency of recent 40 years precipitation exists a variation that the western is in contrast to eastern, the west part of northwest china exists a obvious increase tread, and in the east part decrease tread. By using REOF method, the abnormality type of annual precipitation in northwest china can be divide into 6 key regions: Northeast Qinghai Xizang Plateau,Northern Xinjiang,Eastern Qinghai,eastern part of Northwest China ,Southern Xingjiang and Gansu Corridor.., The period analyze for time coefficient series of EOF' first principal component and time coefficient series of 6 regions that accord with REOF reveals that 3-yeas period variation of precipitation in most of northwest china dominated, then 6-8years periodic oscillation.,(2) In northwest of china intra-annual distribution of area mean precipitation show that: it is the most in summer; it is appropriate in spring and autumn; it is minimum in winter, monthly precipitation is the most in July and show quasi-normal frequency, By analysis annual ten days to ten days precipitation we found that the rainy spell is the first ten days of May to the first ten days of October. But rain period is the first ten days of July to the first ten days of September,, Of all the climatic anomaly regions,north Xinjiang region is different, from other regions, monthly and seasonal precipitation are well distribution, by comparison spring precipitation is the most,next is summer, autumn, winter.South Xinjiang region, north of Xinjiang region and Hexi corridor region havn't rain spell, others regions's rain spell is the first ten days of July to the first ten days of September.(3) Recent 40 years the main feature of intra-seasonal distribution of all regions precipitation show that: the linear change tendency of recent 40 years precipitation in north Xinjiang region are positive, but autumn precipitation of others regions exist obvious descend tendency.. Moreover the spring precipitation of all the regions exist 3-4 yeas periodic variation.(4) By using of the distribution of Gumbel fitting extreme precipitation of the...