京津冀城市群热岛定量评估

Research on quantitative evaluations of heat islands for the Beijing-Tianjin-Hebei Urban Agglomeration

在采用城乡二分法估算区域范围内多个城市地表热岛强度(Surface Urban Heat Island,SUHI)时,如何选择城镇化影响最小的周边乡村背景是一个技术难点,提出了一种基于地形、土地利用、植被覆盖和城市夜间灯光指数来确定乡村背景的SUHI估算方法,并建立了基于SUHI和热岛比例指数(Urban Heat Island Proportion Index,UHPI)的城市热岛强度定量评估方法。利用上述方法,基于长时间序列MODIS和NOAA卫星资料,开展了京津冀城市群11个平原城市热岛时空变化分析与评估,并开展了社会经济驱动因子对城市热岛大小的影响评估研究,同时结合未来京津冀一体化发展提出相应参考建议。研究结果表明:(1)建立的SUHI估算方法能有效监测城市群热岛年/季和昼/夜变化,近5年(2010—2014)年均SUHI≥3℃的热岛总面积1926km^2,但在热岛最强的夏季白天可达7386 km^2(占行政区域面积的5.8%);排名前四的分别是北京(2351 km^2)、天津(1883km^2)、唐山(889 km^2)和石家庄(611 km^2),显示出超大、特大城市及资源性城市贡献了大部分城市群热岛面积;各中心城区平均SUHI和UHPI分别为3.0℃和0.61,热岛评估达到较严重等级以上的城市占到73%,表明当前城市群整体热岛处于严峻现状;(2)1994、2004年和2014年夏季白天城市群强热岛面积分别为190、1975、4539 km^2,各中心城区平均SUHI分别为1.2、2.6、3.2℃,UHPI分别为0.29、0.58和0.69,热岛评估等级分别为"一般"、"较严重"和"严重"等级,反映了20年来京津冀城市群热岛迅速增强增大事实;(3)各城市年均热岛面积增加2—86 km^2/a,强热岛面积增加主要发生在超大城市,北京、天津强热岛区之间的最短空间距离从1994年的94 km逐步缩减到2014年的52 km,未来存在形成"京津区域热岛群"的可能,建议在京津之间建立"绿色生态屏障"来消除这种可能性;(4)城镇人口数、国内生产总值和用电量都极大地影响着京津冀城市热岛大小,拟合模型决定系数R2分别为0.9097、0.912和0.9661,意味着在未来京津冀一体化城市发展中可采取控制城市人口规模、减少能源消耗等措施减缓热岛效应。

When estimating surface urban heat island intensity （SUHI） of different cities on a regional scale using the urban-rural difference method, it is technically difficult to select the rural districts or reference areas that exhibit minimal impact by urbanization. In this study, we propose a method of estimating SUHI based on land topography, land use, vegetation coverage, and urban nighttime light index to define the rural districts. Then, a quantitative evaluation method can be established to determine heat island intensity based on SUHI and the urban heat island proportion index （UHPI）. Using this method, the temporal and spatial variation of urban heat island for the Beijing-Tianjin-Hebei urban agglomeration region was quantitatively evaluated based on long time series MODIS and NOAA satellite data. An impact assessment for socio-economic factors driving urban heat islands was also conducted, and some recommendations for Beijing-Tianjin-Hebei economic unity development are proposed. The results show that the SUHI estimation method can effectively reflect annual, seasonal, and diurnal variations of heat island in urban agglomerations. The annual mean heat island area with SUHI greater than or equal to 3.0℃ from 2010-2014 was 1,926 km2. It is highest on summer days at 7386 km2 （5.8% of total urban group area）. The four largest area cities are Beijing at 2351 km2, Tianjin at 1883 km2, Tangshan at 889 km2, and Shijiazhang at 611 km2, which represent megacities, extra-large cities, and resource-dependent cities contributing to most of the heat island areas. The mean SUHI and UHPI of all central urban areas are 3.0℃ and 0.61, respectively. Seventy-three percent of cities have heat island assessment levels that are more than relatively severe with SUHI greater than or equal to 3.0℃. This indicates that the phenomenon of heat islands in urban agglomeration is currently severe. During summer days in 1994, 2004, and 2014, the areas with SUHI greater than or equal to 5.0℃ were 190 km2, 1975 km2, and 4539 km2; the mean SUHI were 1.2℃, 2.6℃, and 3.2℃; and the UHPI were 0.29, 0.58, and 0.69. The heat island assessment levels were normal, relatively severe, and severe, respectively, which reflects the fact that the heat island effect for urban agglomerations has strengthened and expanded in the last 20 years. The annual growth rate of heat island areas is 2-86 km2/a, and the increasing areas of high-level heat islands in urban group regions occur mainly in megacity behemoths. The shortest distance between the Beijing heat island region and the Tianjin heat island region was reduced from 94 km in 1994 to 52 km in 2014. Thus, in future, the Beijing and Tianjin heat island regions will probably connect to form a new Beijing Tianjin heat island group, which may be an ecological disaster for urban agglomeration development. Therefore, an ecological green barrier between Beijing and Tianjin should be set up to halt the trend. Heat island area with SUHI greater than or equal to 3.0℃ for various cities correlate notably with the urban population, gross domestic product, and electricity consumption, and the R2 are 0.9097, 0.912, and 0.9661, which indicates the important role of population control and energy consumption reduction in the development of the Beijing-Tianjin-Hebei economic unit.