Research On Urban Heat Island Effect And Its Mitigation

Urban heat island effect (UHI) is a local phenomenon that the central temperature ishigher than that of suburbs. It is due to human activities. Shijiazhuang city has beenexperiencing a rapid development in nearly20years. Its UHI appeared complexcharacteristics. The study chose three different periods of remote sensing image recordedon1990,2001and2010. ENVI and ArcGIS software were used for information extractionfrom the results of decision tree classification and land surface temperature inversion. Thespatial and temporal distribution characteristics and quantitative researches on differentunderlaying surface were analyzed. And then the quantitative relations on cooling effect ofcity parks were studied. Finally mitigation strategies were put forward based on theanalysis of urban heat island effect.Results show that there are differences on the spatial distribution of UHI aboutShijiazhuang in nearly20years: in1990, there is only one UHI peak which is in the centreof the city, and on the whole it is present circular distribution; in2001, as a whole it is stillpresent circular distribution characteristics, at the same time, a cross-shaped high UHI areaappeared along the Beijing-Guangzhou Railway and Shijiazhuang-Taiyuan Railway.While the spatial distribution of UHI in2010presents strip and dispersed multi-centercharacteristics. There is significant positive correlation (R2=0.8184) between thepercentage of impervious surface (ISA%) and land surface temperature (LST), but not inlinear correlation, while in accordance with quadratic polynomial relations; as well as therelationship of steel framed roof proportion and LST (R2=0.7056), which in accordancewith cubic polynomial relationship; the relationship of vegetation proportion and LSTappears negative correlation (R2=0.8264), which is also in accordance with quadraticpolynomial. The change rate of surface temperature depends on the proportion of differentunderlying surface, urban thermal environment effect will decline when ISA%reach40%;steel framed roof tend to follow similar patterns, while vegetation in contrast. Coolingeffect of parks is obvious while there are differences. Each fitting curve of park coolingamplitude is in conformity to quadratic polynomial and the fitting degree is high. Coolingscope, cooling amplitude and cooling rate are significantly related to total area, water areapercentage, imperious surface area percentage respectively. It is significant for UHImitigation in urban planning which designing park area around32ha, controlling water area proportion more than19%and impervious surface percentage less than50%. Finally,the mitigation strategies are put forward including: increasing roof reflectance, city parklandscape and greening rate, reasonably planning of urban development mode, buildingthe urban space structure which could ventilate and dissipate heat easily, reducing theoperation energy consumption of the city.