Study On The Thermal Effect Of Green Land And Its Function Of Urban Heat Island Mitigation In Ma’anshan City

The urban thermal environment dynamic of Ma’anshan city, an important iron and steel industrial city, in the period of2007and2010was analyzed using the RS technique in this paper, and the affects of urban hill forest and parks on urban heat island were illustrated, all data was collected by determinant of TM images of Satland7in2007and2010. The study area covered315km2with build-up area of67km2, all works were done using ArcGis9.2. The research should provide a certain guidance and reference for urban forest planning and constructing having a purpose to Urban heat island mitigation.The results as follows:(1) From ground brightness temperature distribution of Ma’anshan in2007, the higher thermal field main existed in the built-up area, which made up the center "heat island". In which the high temperature zone and secondary high temperature zone were concentrated in the old city zone, residential squares, and industrial areas of old city zone and so on, the main distribution was the central and western area of the city. Comparison to the2007situation, the total area covered by high temperature zone and secondary high temperature zone was reduced in2010, And their distribution feature changed from the shape of slice or block in2007to that of point, paste in2010, the area of low temperature zone was increased in2010.(2) Based on the comparison of heat island patterns combined with land use maps between2007and2010,we can made a conclusion that urban green coverage was increased in2010, the area increasing of urban forest and the general green land is good for Urban heat island mitigation. Also we found that the higher greening coverage in a region, the higher percentage of low-temperature field is, then the heat island effect is lower.(3) With quantitative analysis, a negative correlation between the heat island effect and Normalized Difference Vegetation Index (NDVI) for different types of vegetation was described by mathematical model, as NDVI of urban forest elevates0.1, the ground brightness temperature drops0.852℃; NDVI of general green land elevates0.1every time, the ground brightness drops0.11℃. Generally, the heat island mitigation effect of urban forest patch is higher than that of general green land.(4) The effect of the hill forest patches to the thermal field had a radial range:The ground brightness temperature increased with increasing the distance from hill forest, the increasing level was higher at first then lowered down, then it approximately constant as the distance increasing furthermore the distance from hill forest patch that ground brightness temperature begging to get constant value was called critical value in this paper, the critical value has great relevance to forest patch area. And the radial range of thermal field for urban forest patches increased with increasing of patch area. This relationship was described as Y=3.567X+418.75, R2=0.8498. The author suggested that increasing area of forest patch was a good way for reducing the ground bright temperature. The author estimated that the radiation distance of hill forest increased356.71m and that of parks increased311.77m, as the area of patches increased100hm2.(5) From the model chart of the hill forest patches, parks patches and the total biomass, we can get that, the ability of the factors which effect the radiation distance of hill patches as follows, the total biomass of patches>the area of patches>the perimeter of patches, it had no significant relationship with patch shape. Increasing the total biomass of hill forest patches made advantages to expand radiation range.(6) It was discovered that the land types around the forest or general green land patches made effect to the radiation range of reducing ground bright temperature, Among dominant factors, there was a positive correlation between the urban forest and radiation range, also a negative correlation between the buildings and the radiation range. The radiation range expanded as the area of urban forest coverage around the patches increased, while that reduced when the area of buildings expanded.