植被、不透水面、水体对喀斯特城市地表热场影响

针对桂林喀斯特城市快速扩展所引发的热环境和热岛问题，对1989年和2006年TM卫星图像利用模型反演地表温度、植被指数NDVI、不透水面率ISA和水体指数MNDWI，分析植被、不透水面、水体等3个因素时间和空间变化对地表热场的影响机理。结果表明，地表温度与NDVI、MNDWI呈明显的负相关关系，与ISA呈明显的正相关关系；1989--2006年研究区NDVI大于0．4的中高植被覆盖区由76．89％大幅度降低到32．65％，NDVI低于0．2的无植被覆盖区由4．01％大幅度升高至17．15％，水体面积由3．87％降低到1．95％；ISA大于0．9的高不透水区域由12．1％大幅度升高至32．1％，导致地表温度高温区和次高温区由7．9％大幅度升高至15．9％，低温区和次低温区由61．8％大幅度降低到38．9％，热岛现象明显增强。连续大面积的不透水面是产生喀斯特城市热岛效应的直接原因，而喀斯特山峰植被、城市林地与行道树、城市中江湖等较大水体，对喀斯特城市热岛效应的缓解具有非常重要的作用。

Influence of Vegetation,Impervious Surface and Water Body on Land Thermal Fileld of Karst City

In order to evaluate the impact of karst Guilin City rapid expansion on urban heat island effect, land surface temperature （LST）, seven vegetation indexes （VI）, percent impervious surface area （ISA） and modified normalized difference water index （MNDWI） were retrieved with model from TM image. After the influcence of temporal and spatial variation of vegetation, impervi- ous surface and water body on land thermal field of karst city was studied. Results show that there is a significant negative linear re- lationship between LST and VI, so is between LST and MNDWI. Howerver, the relationship between LST and ISA shows signifi- cant positive linear. From 1989 to 2006, the medium and high vegetation covered area of NDVI~O. 4 slashes from 76. 89% to 32.65%, and the area without vegetation coverage of NDVI〈0. 2 rises from 4.01% to 17.15%. Meanwhile, the area of water drops from 3.87% to 1.95%, and the high impervious surface of ISA〉0. 9 rises greatly from 12.1% to 32.1%. Those result in the high and sub-high surafce temperature areas rises from 7.9% to 15.9%, the low and sub-low surafce temperature areas drop substantially from 61.8 % to 38.9 %. Urban heat island effect markedly enhanced. Continuous large impervious surface area is one of the main factors contributing to urban heat island on karst city. But Vegetation on karst hills, urban forest and large water bodies such as rivers and lakes have very great impact on karst urban thermal environment and mitigate urban heat island.