中国城市热岛时空特征及其影响因子的分析

全球气候变暖背景下,城市热岛效应会加重城市地区的热胁迫,对人类健康和生存发展提出严峻挑战.近年来我国雾-霾污染情况严重,但雾-霾对城市热岛影响的认识仍较匮乏.本研究基于MODIS遥感卫星地表温度数据,明确了我国2003~2013年白天、夜间以及四季城市热岛的空间变化,并从生物物理学和生物化学角度定量分析其控制机制.结果表明,影响我国白天城市热岛强度的主要因素为人口、农田灌溉和植被活动.纬度、降水量、反照率以及气溶胶浓度是夜间城市热岛强度的主控因子.从对比城乡粗糙度、反照率等生物物理学属性的角度,揭示了乡村背景环境对城市热岛分析的重要影响.结果表明,雾-霾治理可以缓解我国夜间城市热岛现象和热胁迫,有利于缓解区域甚至全球气候变化.

Correlation Analysis of the Urban Heat Island Effect and Its Impact Factors in China

Urban heat islands (UHIs), which are urban areas with higher surface or air temperatures than surrounding rural areas, can further enhance the heat stress already exacerbated by global warming. This poses great challenges to human health and sustainable development. China has been burdened with heavy air pollution in recent years, and the effect of haze pollution on UHIs is still far less well understood. This study investigated the spatial variations of daytime, nighttime, and seasonal surface UHI effects in China during 2003-2013, based on MODIS land surface temperature data, and analyzed the correlations between the UHI effect and its impact factors from both biophysical and biochemical perspectives. Our results show that MODIS-derived annual nighttime UHI effect (3.4 K±0.2 K, mean±1 s.e.) is higher than the annual mean daytime UHI effect (2.1 K±0.3 K). The daytime UHI effect is strongest in summer and weakest in winter but contrasts with the seasonal variation characteristics of nighttime UHI effect. During daytime, UHI effects in humid and semi-humid regions are much more obvious than those in semi-arid/arid regions; during nighttime, the UHI effect in semi-humid and semi-arid/arid regions is much stronger than that in humid regions. A Daytime Urban Cool Island effect exists in semi-arid/arid regions during spring, autumn, and winter seasons. Population, vegetation activity, and irrigation are three factors controlling annual mean daytime UHI effect. The nighttime UHI is significantly influenced by latitude, albedo, precipitation, and aerosol concentrations. We provide evidence for a long-held hypothesis that the biogeochemical effect of urban aerosols is an important contributor to the UHI effect. The important role played by rural background environment in calculating the UHI effect is further discussed in terms of surface aerodynamic roughness and the contrast in albedo between urban and rural areas. Mitigation of haze pollution has a co-benefit of reducing the UHI effect and heat stress for urban dwellers. It is also conducive to reducing negative impacts of regional and global climate change.