Analysis On The Influence Of Land Use On City Thermal Environment

With the background of rapid urbanization, the population living in urban areas has been increasing rapidly; urban building density has improved significantly and more and more people are focusing on urban thermal environment which represented by urban heat island (UHI) effect. Urban heat environment has triggered a series of negative utility of thermal environment, so that urban ecological environment and residential environment are deeply influenced. Urban thermal environment is not only climatic environmental issues, but a big hurdle for the urbanization process and the sustainable development of urban ecological environment.The study take the Wuhan main urban area and its surrounding area as the studied area and collect Landsat TM images and six periods of land use datasets of Wuhan. Then the article analyses temporal-spatial characteristics of land use and UHI during the period of 1990-2013, and on this basis explored the relationship between urban land use and urban heat environment. The study also quantitatively analyses the influence for the urban land use/cover type on UHI effect combined with relevant methods. Significant findings of the paper are as follows:Firstly, the characters of land use change in Wuhan during 1990-2013 are shown as these aspects:in quantity, cultivated land and forest land decreased each year, while construction land increased every year and forest land, grassland, water area and unused land undulated slightly over time; construction land and cultivated land changed obviously in speed and range; cultivated land has made a great contribution to the transformation of other land use types to urban construction land. About urban construction land in Wuhan, it has increased by 458.06km2 (from 283.41km2 to 741.46km2) during 1990-2013 and the area expanded is 2.62 times the area of 1990. On the space pattern, the newly construction land sprawled along the multi axis with a radiate structure around the center city on the edge of town. The urban centers were spreading outward, new urban areas’ construction developed rapidly, and crisscrossed road traffic system linked up the whole area.Secondly, low temperature zone and sub-medium temperature zone of Wuhan during 1990-2013 were distributed in water area and its surrounding area, and medium temperature area was apparent in the cultivated land and grassland on the urban periphery, while high temperature zone and sub-high temperature zone were concentrated in urban built-up area where are the most densely populated and prosperous business part of the country and its land surface temperature(LST) are higher than the surrounding area obviously. The spatial variation of urban thermal environment and spatial expansion of built-up area in Wuhan were in a good time-space consistency, and it manifested as that there were local high or sub-high temperature heat island with new urban area at the core dispersed over outside of the high temperature heat island area in central urban area. Besides, during 1990-2013, most of the stable regions of urban thermal grade were low temperature zone and high temperature zone, while the unstable regions were medium temperature zone and sub-high temperature zone. Changes of UHI area and the growth of construction land had consistency, and urban expansion was the most direct and fundamental driving force of the extension of UHI area.Thirdly, in the aspect of the response of urban LST to land use types, the highest mean LST was in the urban construction land, the value was 30 ℃ or above, while the mean LST of waters was lowest, the value was about 25 ℃. About the response of urban heat effect spatial variation to land use types, there was variability among LST with different land use types, and there was obvious indicative of different land use type to urban heat environment pattern. Medium temperature zone was distributed mainly over cultivated land, forest land and grassland, water area was distributed in each thermal grade interval, among which high temperature zone is the least. Urban construction land distribution was mainly in high and sub-high temperature zone, and rural residential was in sub-high and medium temperature zone, while unused land was in medium and sub-medium temperature zone. It showed little change for proportion of waters in all thermal grade interval during 1990-2013, and waters accounts for less percentage in low temperature zone. The proportion of cultivated land in high and sub-high temperature zone reduced year by year, and it was increased by years about urban construction land.Fourthly, in terms of contribution of land use cover type to urban heat environment, the heating effects contribution of cultivated land dropped gradually as a whole, while urban construction land’s contribution raised gradually during 1990-2013. It showed that the contribution degree of cultivated land and urban construction land was the highest, unused land was the lowest according to thermal effect contribution index; urban construction land was the highest, water area was the lowest according to the thermal elements weighted index; and cultivated land was the highest, unused land was the lowest according to the regional thermal elements weighted index.Lastly, as to the influence of land use change to LST, the impact of land use types encroached by construction land on urban heat environment was ordered in descending order of magnitude:water area, cultivated land, forest land, grassland, unused land and rural residential. It indicated that waters seem to have the strongest effect on mitigating thermal environment, followed by cultivated land, and unused land and rural residential have the weakest influence on LST. Therefore, protecting waters, controlling farmland occupation, developing the unutilized land reasonably, and conducting the renovation of the village residential area well are essential in the urban planning and decision making.