Study On Heat Island Effect Variation And Its Response To Vegetation Eco-environmental Quality In Wuhu City

With the speeding up of urbanization, urban heat island effect has become more serious and it brings us many negative impacts, such as high temperature disaster and atmospheric condition worsening. How to quantitatively analyse variation pattern and influence mechanism of heat island is the foundation and precondition of alleviating heat island effect. Consequently, it is always an important topic in academic interests.As an open door to the outside world along the Yangtze Rive, Wuhu City has possessed remarkable urbanization and industralization since nineties of last century. It turns out with population growing and urban land expanding rapidly. Study on heat island effect variation and its response to vegetation eco-environmental quality in Wuhu City is of great significance. First of all, it may provide scientific grounds for well-considered plan, industrial organization and improvement of vegetation eco-environment. Besides, it can be used for reference to other relevant research in heat island effect.This essay aimed to quantitatively describe spatial and temporal pattern of heat island. Firstly, land surface temperature in Wuhu City was obtained on the basis of remote sensing images of TM, meteorological data and supported by GIS analysis technology. Then various quantitatively methods were combined and applied in following analysis. Meanwhile, considering vegetation eco-environmental problems in Wuhu City and choosing climate background, topography, land cover as assessing factors, an integrated evaluation model of vegetation eco-environmental quality on rid scale was constructed. Finally, the relationship between land surface temperature and vegetation eco-environmental quality was uncovered. The results showed that:(1)The urban heat island in Wuhu City was obvious and existed in the central urban area or core area of subordinate municipal districts, which were the densely inhabited district and industrial park gathering. With the enlargement of urban area, the distribution of heat island became wider from 171.29 km2 in 1995 to 182.81 km2. On the contrary, the distribution of cold island became smaller from 172.78 km2 in 1995 to 152.7 km2 in 2007. Besides heat island intensity turned stronger than before with annual rowth rate of 2.06%.( 2 ) Variation velocity analysis showed that heat island grades changed significantly, and high heat island possessed the greatest variance velocity in particular with 6.46% and 7.77% in Jiujiang district and Yijiang district respectively. But there were prominent differences of variance velocity in different subordinate municipal districts. Yijiang district and Sanshan district possessed higher variation velocity than the whole region, while the others owned lower one.The whole conversion tendency among heat island grades was lower grade turned into higher one, conforming to the basic rule of variation of urban heat island.(3)On regional scale, under the influence of urban planning in Wuhu City, thermal landscape tended to gather and its fractal dimension decreased. In addition, the function of predominant thermal landscape type strengthened. On heat island grade scale, landscape pattern of heat island grades had diversity and multi-directionality. They did not all have the same variation tendency as the whole region. Superiority and stability of high heat island enhanced, while fragmentation decreased. It indicated that urban thermal environment in Wuhu might continue to deteriorate in the future to some extent.( 4 ) Low land surface temperature corresponded to high vegetation eco-environmental quality. Impact of vegetation eco-environmental quality typeⅤon thermal environment became more and more significant and land surface temperature in this region had a lowing standard deviation from 1995 to 2007. In contrast, land surface temperature in other region decreased.(5)Heat island grades had the same vegetation eco-environmental quality constitution in 1995 and 2007. On the whole, higher temperature region corresponded to lower vegetation eco-environmental quality, while lower temperature corresponded to higher one. Vegetation eco-environmental quality constitution of heat island grades had some regular rules: the increasing proportion in higher temperature region was lower vegetation eco-environmental quality, in lower temperature region medium one, and in medium temperature region higher one. ( 6 ) Thermal environmental effect for different types of vegetation eco-environmental quality had obvious discrepancies, with strengthening thermal environmental effect for typeⅠ,Ⅱ,Ⅲ, and weakening thermal environmental effect for typeⅣ,Ⅴ. And their effect turned more significant in study period. Landscape pattern of cooling vegetation eco-environmental quality types influenced land surface temperature significantly. Area percentage and contagion index possessed marked negative correlation with land surface temperature, while diversity index possessed marked positive correlation with land surface temperature.(7)On the whole, there was remarkably negative correlation between land surface temperature and vegetation eco-environmental quality index. Therefore, vegetation eco-environmental quality might regulate land surface temperature effectively, and its regulation was strengthening in study period. But this function of regulation should be divided into two phases. Superior vegetation eco-environmental quality could reduce land surface temperature for higher temperature segment. However, for lower temperature segment, superior one might increase land surface temperature.