宁波城市热岛随城市化演变的多指标综合分析

Multi-index Analysis of Heat Island Dynamics with the Process of Urbanisation in Ningbo City

以宁波市为研究对象,利用1984─2010年间冬、夏各5景Landsat TM/ETM+遥感影像数据进行地表温度反演,在此基础上使用热岛强度、热岛面积、景观格局指数综合分析了宁波城市化进程中城市热岛在冬、夏两季的演变趋势,得出如下结果,(1)强度方面,冬季平均热岛强度为1.57℃,夏季为8.67℃,夏季明显强于冬季;热岛强度在夏季呈增强趋势,在冬季呈变弱趋势。(2)热岛面积方面,在冬季,平均89%的建成区受热岛效应的影响,而在夏季,该比例为98%。无论冬夏,热岛面积均随城市化的发展持续增加。(3)数量方面,热岛景观在冬季以低等级热岛斑块为主,占热岛面积的96%左右,夏季以中、高等级热岛斑块为主,比例约为热岛面积的92%。无论冬夏高等级热岛斑块个数均随着城市化进程显著增加。(4)形态方面,无论冬夏主要热岛景观类型乃至整个热岛的斑块形状均变得更加复杂。(5)结构方面,热岛景观在冬季总体上逐渐破碎化,各类景观趋向均匀,多样性增加。在夏季则逐渐聚集,逐步向以高等级斑块为主导的格局方向发展,多样性降低。(6)空间分布方面,随着城市化进展,冬夏两季热岛景观斑块都经历了数量增加、等级升高的变化。冬季在北仑的宁波经济技术开发区形成了两个热点区,夏季在三江口周边、甬江口两岸以及经济技术开发区形成了三大高温片区。利用多指标综合分析可以更加全面的反映城市热岛的演变规律,为减缓城市热岛效应提供理论依据。

Urban Heat Island （UHI） is one of the most significant environmental issues along with the process of urbanization. It is an effect way to mitigate UHI when considering the dynamic characters of UHI. It is a useful tool to unfold the inherent characters of UHI when using the multi-index analysis. Taking Ningbo as a case study, we use TM/ETM＋ imageries to invert thermal maps both in summer and winter seasons from 1984 to 2010. UHI intensity, UHI extent and landscape metrics within the same period, thereafter, are calculated based on the thermal maps. The results show that： （1） The average UHI intensity is 1.57℃ in winter, which rises to 8.67℃ in summer. The UHI effect is more significant in summer than that in winter. And this effect tends to increase during the summer but decreases during the winter. （2） The share of the built-up areas which is affected by the UHI in winter is 89% and that in summer was 98%. UHI extent kept increasing with urbanization in both winter and summer. （3） In winter, the low – grade UHI patches are the dominant patches, which contain 96% of the total UHI areas, while the dominant patches changes to middle / high – grade patches in summer, containing 92% of the total UHI areas. （4） The patch shape of main UHI classes became more complex with urbanization in both seasons, as well as the patch shape at landscape level. （5） The UHI landscape became more fragmented in winter yet more aggregation in summer. In winter patch areas of different grades turned evener and the whole landscape became more diverse, which was opposite in summer. （6） Both the number and grades of UHI patches increased with urbanization. Two hot – spots emerge in Ningbo Economic and Technological zone during the winter season. And three areas with high temperature place at Sanjiangkou, Yong River estuary and Ningbo Economic and Technological Zone. Those results provide some policy implications for urban management.