The Relationship Between Land Cover/Land Cover Change And Urban Heat Island Under The Rapid Urbanization

Rapid and urgent urbanization process not only leads to the growth of urban population and the expansion of construction land, but also challenges the city’s capacity, causing a series of impacts on the urban environment, such as climate, hydrology, ecology et al. Under the global warming and rapid urbanization, in recent years, urban thermal environment forced by surface physical properties and human socio-economic activities, becomes the comprehensive summary and reflects of urban ecological environment. Urban heat island is a concentrated expression of urban thermal environment, which not only impacts the comfort and health of urban dwellers but also contributes to heat wave disasters. In the 《National Outline for Medium and Long Term Science and Technology Development (2005-2020)》, China presented the formation mechanism and artificial control technology of urban heat island should be one of the most important content in the future researches.Land use and manage will change the natural land cover. Urbanization leads to the different land cover in urban region. Extensively urbanized surfaces modify the energy and water balance processes and influence the air movement, causing the wide and profound impacts on regional atmosphere, boundary layer structure, climate et al. Therefore, study on the relationship between land cover/land cover change and urban heat island will provide the theoretical basis not only for land-use management and urban planning, but also for the survey and analysis of regional urban heat island by the integration of RS and GIS, in order to provide more technical knowledge to deal with the possible global climate change in future.In this research, firstly, land cover and land surface temperature(LST) retrieved from HJ-1B data and air temperature data measured by meteorological stations(Tair) were used to examine the impacts of urban land cover on diurnal Tair and LST, on the relationship of Tair and LST, and on the change of UHI at a fine scale. Secondly, Landsat images were used to detect the land cover change of Hangzhou urban area since1990s, and to qualitatively and quantitatively investigate the impacts of land cover change on the intensity and spatial distribution of urban heat island from two scales—annual and seasonal land cover change. The main results are as follows:1. Retrieve aerosol optical depth (AOD), land cover and land surface temperature from HJ-1B data. Due to the lack of the important band—2.1μm for retrieval of aerosol optical depth by the method of dark object, a method combining the HJ CCD data and IRS2(1.6μm) data was presented to inverse AOD—retrieve dark object from CCD4and the vegetation index of AFRI, simulate the look-up table by6S model, and base on the linear relationship of the reflectance of red band and the reflectance of blue band. Due to the mixed pixel problem in urban environment, a method was presented to retrieve land cover from HJ-1B—First based on the theory of spectral mixture analysis (SMA) approach, four endmembers (high albedo, low albedo, vegetation and blue building roof) were identified; Second iterative ISODATA was used to retrieve land cover from the fraction images of four endmembers; At last the land cover constitution (impervious surface fraction, vegetation fraction, soil fraction and water fraction) of every pixel was acquired. Due to the vacant of the emissivity values for HJ-1B thermal infrared band, the emissivity values corresponding to representative materials for HJ-1B thermal infrared band were given through the calculation of the spectral response of HJ-1B thermal infrared channel and the reflectance of representative materials from ASTER spectral library, and a method utilizing the CCD data to calculate the emissivity values of the mixed pixel was proposed. The generalized single-channel method was used to retrieve LST and the result showed the retrieved LST keeps consistent with the actual surface temperature.2. Impervious surface and vegetation are more significantly related to satellite-based LST and nighttime Tair than to daytime Tair. The percent of impervious surface (short for%IS) and the percent of vegetation (short for%GV) had strongly significant correlation with Tairs and LST, especially with R_Tair at Oam and LST. Strongly significant correlation existed between the satellite-based LST and station-based Tair at10am and Oam. The high correlation of LST and R_Tair at10am is mainly caused by the close acquisition time, because the energy to heat air and underlying surface at about10am mainly rely on solar irradiance. Whereas the energy to heat air at night mainly comes from the long wave radiation of underlying surface. Both impervious surface and vegetation are important factors to connect satellite-based LST and nighttime Tair. And%IS is a better indictor to express the relationship of satellite-based LST and nighttime. We suggest%IS can be a good indicator to connect the AUHI at night to satellite-based SUHI. Urban surface heat island tends to occur in the region with dense construction and high buildings. In daytime, there is no obvious phenomenon of urban atmospheric heat island, but nighttime urban heat island tends to occur in the region with dense construction.3. From the quantification of the spatial distribution of diurnal urban atmospheric heat island in Hangzhou, a livable life is near the cool islands or the area with the larger positive cooling-distance rate, mainly the directions of SW, S, W and NE. The quantification of the spatial distribution of diurnal urban atmospheric heat island includes three steps:1. Simplify the spatial distribution of urban heat island based on the spatial distribution of the location of measured data;2. Quantify the intensity of urban heat island based on the difference between Tair at urban centre and Tair at each location;3. Quantify the spatial distribution of urban heat island by the index of cooling-distance rate, which was first presented by this research. Cooling-distance rate can be a good indicator to guide people to identify a livable place in compromise of UHI and convenient life.4. Detect the temporal and spatial change of land cover in Hangzhou urban area since1990s from a series of Landsat images. Due to the urban expansion, the improvement of people’s life, the protection of government and the adjustment of agricultural structure, the impervious surface area had largely increased, and urban greenland and aquaculture ponds had also increased. A large amount of irrigated land and upland had been occupied, and a small quantity of forest had been also occupied during this period. Xixi National Wetland Park kept stable after protected by government since2000. In the region of East City, West City, Xiasha and Zhijiang, impervious surface expanded towards the suburban directions. In the region of Main City and Binjiang, impervious surface expanded towards the Qiantang River. Urban wetland decreased towards the suburban directions.5. Urban expansion leads to a more intensive urban heat island effect, and a more continuous and centralized hot spots. The ability of boosting urban heat island by the occupation of wetland is stronger than the occupation of vegetation. In Hangzhou urban area, the stronger urban heat island appeared in summer, following by spring and autumn. There is no obvious urban heat island in winter. The ability of boosting urban heat island by different land cover types varies in different seasons.%IS, which is less affected by the season and climate change, can be a better indicator for the seasonal variation of urban heat island intensity.