北京地区降水量时空分布规律分析

Analysis on the spatiotemporal distribution of precipitation in the Beijing Region

通过运用非参数检验方法（Mann-Kendall法）,利用北京地区20个气象站点44年（1961-2004）观测的逐月降水资料,分析了北京地区降水量的时空分布规律.结果表明：在时间上,年平均降水量总趋势以每年1.72 mm的变化率减少,这种减少主要是由夏季、冬季降水量减少所引起的,尤以夏季最为显著,变化率为-3.26 mm/a,而在春、秋两季降水量则呈现出增加的趋势,变化率分别为0.34 mm/a和0.77 mm/a.降水期主要集中于夏季（6～8月）,可占全年降水量的72.5%.在空间上,年降水量的高值区位于山前迎风坡一带,大致呈带状自西南伸向东北,高值区的西北、东南两侧雨量逐渐减少.市区形成一个明显的下降中心,其中海淀区年均减少3.7mm,降幅最大.

The Beijing region is located in an arid and semiarid region. Precipitation is not only one of main sources of water resources, but also one of the main factors affecting the periodic change of water resources over the study area. On the basis of precipitation database collected by 20 meteorological stations in the Beijing region during the period from 1961 to 2004, the spatiotemporal distribution of the long - term trend of precipitation in the Beijing region is analyzed in this paper. The Mann - Kendall test is applied to develop the time series of annual and seasonal precipitation in the Beijing region. The Mann - Kendall statistic test is a rank - based and nonparametric approach and has been widely used to estimate the significance of long - term trends in hydrometeorological time series, such as water quality, streamflow, temperature and precipitation. The study results show that the mean annual precipitation is in a decrease trend and its gradient is - 1.72 mm/a. The annual precipitation reduction is mainly caused by the precipitation reduction in summer and winter, especially in summer, and its gradient is -3.26 mm/a. However, the precipitations in spring and autumn is in an increase trend, and their gradients are 0.34 mm/a and 0.77 mm/a respectively. The rainy season is the period from June to August, and the precipitation in the rainy season occupies 72.5% of the annual precipitation. Spatially, the high annual precipitation occurs in the piedmont windward slopes, and the precipitation increases from the northeast to the southwest. The precipitation decreases gradually in northwest and southeast sides of the high - precipitation area. There is an obvious precipitation- decreasing center in urban area, especially in Haidian District, and the gradient is - 3.7 mm/a.