地形对青藏高原丰枯水年雨季降水量空间分布的影响

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

采用高分辨率的3″数字高程模型及青藏高原东部102个常规气象观测站5～9月份的降水量资料,根据降水随高度分布将站点分为三类,再采用多元逐步回归的方法,建立了青藏高原40年(1961-2000年)逐年雨季降水量与经度、纬度、海拔、坡度、坡向、开放度等6个地理、地形因子关系模型,并以此为基础,分析了三类区域在丰枯水年里的因子系数的变化规律。结果表明,此法建立的关于高原降水量与诸因子之间方程的相关性显著,相对误差20%,平均相对误差4.4%,估算模型的相关系数均通过0.05的显著性检验;海拔低于1 400 m的第一类区域,主要受地形高度和开放度等局地地形的影响,来改变旱涝年的降水分布特征,海拔高度大于3 600 m的第三类区域,主要受开放度和坡度的影响,其他区域主要受地形的海拔、经度和开放度等局地地形的影响;高原季风是影响第三类区域水汽分布的主要因素,在季风加强时,开放度和经度的影响也随着加强,而坡度和海拔的影响减弱,从而使得水汽的局地性分布特征增强,东西分布差异加大,相应地局地降水分布特征加强,东西差异加大。地理地形因子影响大气的水汽输送和大气的垂直运动,从而导致其对空间降水分配的差异。

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.