长三角城市群非均匀性对区域热岛效应影响的数值模拟

Numerical simulation of the impact of inhomogeneity of urban agglomeration in the Yangtze River Delta on regional heat island effect

使用中尺度数值模式WRF3.9/Noah/UCM,对长三角地区无明显天气过程的2013年8月11至17日一周进行数值模拟,采用2013年500 m分辨率的MODIS数据更新土地覆盖资料,依据城镇比例将城市下垫面进一步分类为高中低3种类型,以此研究长三角城市群非均匀性对区域热岛效应的影响。结果表明:长三角城市群近地面气象要素场对城市下垫面的非均匀性比较敏感,平均热岛强度、干岛强度和风速衰减相较于不考虑城市非均匀性分别减小了16.41%、20.04%和6.25%;受背景风场影响,白天城市群的热岛强度弱于夜晚,均有向下游扩展现象,且内陆城市的热岛强度和干岛强度较沿岸区域更强;相比于均匀城市下垫面试验,考虑非均匀城市影响后,整体热岛强度和干岛强度减弱;白天垂直热岛环流结构明显,整体可以伸展至2 km高度,在东南风背景下,热岛上游高密度城市的热岛环流会抑制下游热岛环流发展,考虑城市非均匀性后,上游效应更显著;热岛强度受非均匀性影响在傍晚和夜间最高减弱可达0.2 ℃,且进入较强热岛的时间会推迟,维持时间也将缩短。因此,忽略城市下垫面的非均匀性,可能会高估区域热岛效应。

Using the mesoscale numerical model WRF3.9/Noah/UCM, a numerical simulation was carried out for the week from August 11, 2013 to August 17, 2013 when there was no obvious weather process in the Yangtze River Delta region, and land cover was updated with 2013 MODIS data of 500m resolution. According to the proportion of urban areas, the urban underlying surface is further classified into high, medium and low types to study the impact of their inhomogeneity on the regional heat island effect. The results show that the near-surface meteorological element field in the Yangtze River Delta is sensitive to the inhomogeneity of underlying urban areas. The average heat island intensity, dry island intensity and wind speed attenuation reduce by 16.41%, 20.04% and 6.25%, respectively, compared with those without considering the urban inhomogeneity. Affected by the background wind field, the heat island intensity of urban agglomerations in daytime is weaker than that at night, but both of them extend downstream, and the heat island intensity and the dry island intensity in inland cities is stronger than that in coastal areas. Compared with the test on heterogeneous city underlying surface, and considering the effect of inhomogeneity on the urban environment, the heat island intensity and dry island identity weaken on a whole. The structure of the vertical heat island circulation during daytime is obvious, and the overall structure can extend to a height of 2 km. With the southeast wind, the heat island circulation in the high density urban areas of the upper reaches on the heat island will restrain the development of the downstream heat island circulation. Considering the urban inhomogeneity, the upstream effect is more significant. The heat island intensity is affected by the inhomogeneity in the evening and at night, and can be weakened up to 0.2 ℃. Besides, the time to become a stronger heat island will be delayed, and the holding time will also be shortened. Therefore, neglecting the inhomogeneity of urban underlying surface may overestimate the regional heat island effect.