从不同的陆面资料看城市化对北京强降水的影响

NUMERICAL SIMULATION ON IMPACTS OF URBANIZATION ON HEAVY RAIN IN BEIJING USING DIFFERENT LAND USE DATA

2004年7月10日,北京地区出现了一次强降水过程。该次过程主要是由中尺度对流云团的活动造成的,整个大环流形势给暴雨的发展提供了水汽条件。分析近地面的特征场发现,在降水发生前1—2h,北京城区存在一个暖中心,其温度比周边地区高出2—3℃,存在明显的热岛现象。该城市热岛现象的出现,使得城区的气压相对较低,郊区有较冷空气向城区辐合,有利于城区产生上升运动,形成对流降水。另外,对该次过程的数值模拟结果表明,使用了最新的陆面资料的模拟结果明显好于没有使用最新的陆面资料的模拟结果。这在一定程度上说明了城市热岛效应对该次强降水具有一定的影响。

A summer strong convective precipitation event on 10 July, 2004 over Beijing is numerically simulated in this paper, and the impact of UHI on summer convective rain studied. The analysis reveals that a mesoscale convective cloud cluster system brought about the heavy rain, suggesting the supply of moisture by the large scale circulation Before the initiation of precipitation, a generally weaker UHI of 2 - 3℃ existed in the urban area. Much like a sea breeze, the anomalously warm urban air created relatively low pressure, inducing the inflow of cooler rural air towards the urban center, which is favorable to the ascending motion and the formation of convective precipitation over the urban area. In addition, the numerical simulation of the strong convective precipitation event suggests that the simulated result of precipitation using the 2002 LANDSAT-7 landuse data of 30 m resolution is much better than that using the 1993 USGS landuse data of 1 km, whether in rainfall or in the precipitation location. And therefore the simulation confirmed to some extent that the UHI played an important role in the strong precipitation event.