城市化进程对北京地区降水的影响分析

Impact of urbanization on precipitation in Beijing area

用北京20个基本气象站1978—2009年的日降水观测资料以及北京地区水文总站遍布全市的82个雨量站资料,讨论了北京地区降水分布的特征及其城市效应的影响。得到如下结论:(1)北京地区降水量的贡献以中雨以上降水为主。30多年来各级降水除了中雨趋势不明显以外,其他都呈现减小趋势。北京地区降雨量的减少,主要是由于大雨以上量级雨量减少所造成的。(2)近30 a来整个区域降水日数呈减少趋势:西部、西北部及北部山区降水日数较多,越靠近城区降水日数越少。(3)当大尺度降水系统较弱或者局地性强降水系统时,城市效应明显,即相对于区域平均而言,城区及下风方局地降雨增加;而大尺度天气系统较强时,城市效应基本被掩盖。(4)从强降水分布看,1980s以后随着城市化进城加快,短时强降雨局地性特征明显,降雨分布不均,降雨中心的面积和强度明显缩小。这种分布可以在城市热岛分布特征上得到一些合理的解释。

Based on daily precipitation data from 20 basic meteorological sites during 1978—2009 together with hourly precipitation intensity data from 82 hydrological sites in Beijing,the temporal and spatial distribution of rainy days,precipitation amount change for different classification and precipitation intensity,are analyzed.The main conclusions are that：（1）Moderate or heavier rain should play a major role in precipitation.Except moderate rain,the precipitation amount attributable to other kinds of precipitation show a decreasing trend,so decreasing precipitation amount in Beijing area should be induced by less heavy rain,torrential rain,and heavy torrential rain.（2）According to the statistics results,west,northwest and north mountainous region have more rainy day than the region close to urban,the more close,the less rainy days.The rainy days in the whole region keep decreasing for over past 30 years.（3）For large-scale weak precipitation or local strong precipitation,urban effect is obvious,and local rainfall in urban and leeward area increased;while under the large-scale strong precipitation condition,urban effect could not be found.（4）According to analysis,after 1980swith the urbanization accelerating,characteristics of local strong rainfall are more and more obvious,the rainfall distribution is nonuniform and both intensity and area of the precipitation core tend obviously to decrease,which can be explained by distribution of urban heat island.