Abstract: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.