Jiangsu Key Laboratory of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing 210044, China.
Department of Engineering, University of Perugia, via G. Duranti 93, 06125 Perugia, Italy.
Sci Total Environ. 2018 Jul 1;628-629:415-429. doi: 10.1016/j.scitotenv.2018.02.074. Epub 2018 Feb 13.
Increasingly urban agglomeration, representing a group of cities with a compact spatial organization and close economic links, can rise surface temperature in a continuous area due to decreasing distance between cities. Significant progress has been made in elucidating surface urban heat island intensity (SUHII) of a single city or a few big cities, but the SUHII's patterns remain poorly understood in urban agglomeration regions. Using Aqua/Terra MODIS data over 2010-2015, we examined the SUHII variations and their drivers in Yangtze River Delta Urban Agglomeration (YRDUA) of east China. Instead of using the widely-used suburban/rural areas as references, this study predicted the unaffected reference temperature wall-to-wall from natural forests by a simple planar surface model. Results indicated that urbanization warmed the land surface regardless of urban area size in YRDUA, with the SUHII clearly larger in the day (2.6±0.9°C) than night (0.7±0.4°C). The SUHII varied markedly by cities, yet the largest did not happen in the presumed core cities. Also, the SUHII differed greatly in a seasonal cycle, with summer-winter difference of 4.2±0.9°C and 2.0±0.5°C in the day and night, respectively. Particularly, cooling effects of urban areas were observed in winter for the majority of cities at night. These spatiotemporal patterns depend strongly on the background climate (precipitation and air temperature), vegetation activity, surface albedo, and population density, with contrast mechanisms during the day and night. Further, we showed that ignoring urban agglomeration effect (using suburban/rural areas as the unaffected references) would lead to large biases of SUHII estimates in terms of magnitude and spatial distribution. Our results emphasize the necessity of considering cities altogether when assessing the urbanization effects on climate in an urban agglomeration area.
日益壮大的城市群，代表了一组城市，这些城市具有紧凑的空间组织和紧密的经济联系，由于城市之间的距离不断缩小，可能会在一个连续的区域内升高地表温度。在阐明单个城市或少数大城市的地表城市热岛强度（SUHII）方面已经取得了重大进展，但在城市群地区，对 SUHII 的模式仍了解甚少。本研究使用 2010-2015 年期间 Aqua/Terra MODIS 数据，考察了中国东部长江三角洲城市群（YRDUA）的 SUHII 变化及其驱动因素。本研究没有使用广泛使用的郊区/农村地区作为参考，而是通过一个简单的平面表面模型，从天然森林中预测不受影响的参考温度墙壁到墙壁。结果表明，无论城市面积大小，城市化都使土地表面变暖，YRDUA 的 SUHII 在白天（2.6±0.9°C）明显大于夜间（0.7±0.4°C）。SUHII 在城市之间差异明显，但最大的城市并不在假定的核心城市。此外，SUHII 在季节性周期中差异很大，白天和夜间的夏季-冬季差异分别为 4.2±0.9°C 和 2.0±0.5°C。特别是，在夜间，大多数城市在冬季都观察到了城市地区的降温效应。这些时空模式强烈依赖于背景气候（降水和气温）、植被活动、地表反照率和人口密度，并且在白天和夜间存在相反的机制。此外，我们还表明，忽略城市群效应（将郊区/农村地区作为不受影响的参考）会导致 SUHII 估计值在幅度和空间分布方面存在较大偏差。我们的研究结果强调了在城市群地区评估城市化对气候的影响时，需要整体考虑城市的必要性。
