Influence of terrain on precipitation distribution in Qingzang tableland in wet and dry years

Combined 3" digital elevate model(DEM) data with the precipitations of 102 stations in the east of Qingzang tableland from May to Nov.,based on the relation of precipitation distribution with altitude,the stations are divide into three parts,and the relatioships between the rainy season precipitations of 40 years(1961-2000) and six factors longitude,latitude,altitude,gradient,direction of slope and opening are established by using the stepwise regress method.Based on the relationships(models),the change laws of every factor's coefficiency in wet and dry years are analyzed.The result show that the relativity of the models are remarkable:the relative error is less than 20%,average value of relative error 4.4%,and the relativity passes by 0.05 test.The precipitation distribution in wet and dry years is influenced by altitude and opening in the first region with less than 1 400 m altitude; as for the second region with more than 1 400 m altitude and less than 3 600 m altitude,the precipitation is influenced by altitude,longitude and opening,as for the third region with more than 3 600 m altitude,the precipitation is influenced by opening and gradient.When the tableland monsoon becomes strong,the influence of opening and longitude on precipitation is more remarkable,and the influence of gradient and altitude is weaker,therefore,the regional character of water-vapor distribution is notable,the difference in the east and the west become more obvious,so did the precipitation.Therefore,the geographical and topographical factors influence upright motion of atmosphere,which results in difference of precipitation distribution.