Abstract:

Based on observation data including mean temerature，precipitation and rainfall days in summer and winter，wind direction information at each station obtained from Xi’an and its surrounding meteorological stations during 1966 － 2005，as well as hourly precipitation at Xi’an station，the inter － decadal variation of the urban heat island effect and its influence on regional precipitation were analyzed by using statistical comparison method，in addition，a brief analysis and discussion on the causes of the effect was made inthis paper． The results are as follows : ( 1) Heat island is obviously formed in Xi’an in summer and winter because of city expansion，the temperature gradient between the center of Xi’an and its surrounding regions is increasing，and both the intensity and influence sphere of urban heat island effect are larger in winter than those in summer; ( 2) The spatial temperature anomaly difference ( 0 ℃ line) in both summer and winter appears to be an Ω pattern and there is a cold zone or cold center at its east and west sides． The warm center in winter is stronger than that in summer，and western cold center is stronger in summer，but eastern cold center is stronger in winter． And the first distribution characteristic of precipitation in both summer and winter is that the precipitation in cold centers at eastern，western and southern sides of the Ω pattern increases and that at the northern side decreases． The second characteristic is that the amount of precipitation is larger in southwest and smaller in northeast in summer，and larger in eastern region and smaller in western region in winter． Besides，there are local differences in some stations in both summer and winter; ( 3) The seasonal distribution difference of precipitation is caused by prevailing wind change in winter and summer，and the complex spatial distribution of the precipitation is caused by different prevailing wind direction because of topography．

Key words:  basin, topography, urban heat island effect, precipitation

摘要：

利用陕西省西安市及周边14 个气象观测站最近40 a( 1966 ～ 2005 年) 冬季( 12 ～ 2 月) 、夏季( 6 ～ 8 月) 平均气温、降水量和降水日数、各站风向资料及西安站逐时降水资料，运用统计对比分析方法，研究城市热岛效应的年代际变化及其对区域降水的影响，并尝试给予简要的原因分析与讨论。结果表明: ( 1) 由于城市规模的发展，冬夏季均形成了以西安为中心的明显“热岛”，西安城区与临近区域的温度梯度在加大。热岛强度、影响范围冬季强于夏季; ( 2) 无论冬夏季，温度空间距平差0 ℃线都呈Ω 形，在其东西2 侧分别有冷中心或冷区，暖区( 暖中心) 冬季强于夏季，西侧冷区( 冷中心) 夏季强于冬季，东侧冷区( 冷中心) 冬季强于夏季。冬夏季，降水总体分布的第1 特征是: 在Ω 形东、西、南侧冷中心( 冷区) 降水量均增加，在暖舌北侧均减少; 总体分布第2 特征为: 夏季东北少、西南多，冬季西少东多。2 季节都存在个别站点的局地性差异; ( 3) 第1 特征的形成机制是明显的“温度锋区”;第2 特征形成机制是由热岛效应和季节性变化的环境风场间相互作用，降水的季节空间分布差异是由冬夏盛行风变化引起的; 因地形造成盛行风方向的不同是导致降水空间分布复杂的主要原因。

关键词: 盆地, 地形, 热岛效应, 降水