Abstract:

In order to study the effect of urbanization and lakes on the urban heat island (UHI) effect of cities in Yunnan midland in summer, the weather research forecasting model (WRF) numerical model is used. The downwind urban heat island is found in these cities in the summer night. The expansion of city will expand the scope of the downwind urban heat island, but the intensity of the heat island would not be enhanced significantly. The presence of the city will change the surface roughness, resulting in the reduction of wind speed near the surface. In the daytime, lakes and the city influence surface wind speed by changing the local thermal difference. The existence of city increases the thermal difference between city and lake, which enhances both the lake-land breeze and the surface wind speed. The presence of city will reduce the supply of low-level moisture, but the impact of urban expansion on moisture is relatively small. In the early morning, the wet island exists in the city (humidity in city is slightly larger than the surrounding area), due to the convergence filled near surface. At other moments, the dry island exists in the city (humidity in city is smaller than the surrounding area), and has the downwind effect as well.

Key words: urban heat island, lake-land breeze, WRF model, Dianzhong region

摘要：

为了探究滇中地区不同城市化程度和湖泊下垫面对城市热岛效应的影响, 利用中尺度气象模式 WRF (the weather research and forecasting model)对昆明等城市的夏季城市热岛效应进行模拟研究。结果显示, 夏季夜间, 昆明等城市的热岛现象具有明显的下游效应, 城市的扩张使得城市热岛下游效应的影响范围扩大, 但热岛的强度不会明显地增强。城市的存在会增加地表的粗糙度, 使得夜间的近地面风速减小。在白天, 湖泊和城市下垫面主要通过改变局地的热力差异影响近地面的风速, 城市的存在会加强湖泊与陆地间的热力差异, 促进湖陆风环流, 进而加大近地面的风速。城市的存在还会减少下垫面对低层水汽的供应, 但城市面积的增加对低层水汽的影响相对较小。清晨, 城市地区表现为湿岛(湿度较周边地区略大), 这与城市地区的近地面辐合流场有关; 而在其他时段, 城市地区多为干岛(湿度比周边地区低), 且干岛现象也存在下游效应。

关键词: 城市热岛, 湖陆风, WRF模式, 滇中地区