Case Study On The Correlation Of The Thermal Environment And Urban Green Space In Nanchang China

With the increasing process of urbanization, the city area of Nanchang is expanding with a high intensity of population, thus forming a unique micro-climate characteristic of urban thermal environment effect. Based on the TM remote sensing data and relevant meteorological data of Nanchang and field investigation, this dissertation studies the time and space distribution of urban thermal environment of Nanchang, the causes of urban thermal environment and its harms, the correlation between urban thermal environment and urban green space, and the roles of different types of urban green space with different characteristics playing in reducing effect of urban thermal environment. The purpose of this study is to provide reference to quantitative research of urban green space system planning and construction, to provide the scientific basis for reasonable planning and construction of urban green space system and the future formulation of relevant design specification, and also to provide scientific reference for the ecological environment construction and sustainable development of society and economy of Nanchang. The major work accomplished in this research and the main conclusion is summarized as follows:1. The Characteristics of Time and Space Distribution of Urban Thermal Environment in Nanchang(1) Characteristics of Interdecadal VariationThe average temperature of Nanchang is 18.0℃ from 1981 to 2009. The average temperature of 1990s is higher than that of 1980s by 0.4 ℃, and the average temperature of the first decade of the 21st century is higher than that of 1980s by 0.7 ℃. The average temperature continues to increase in recent years.(2) Characteristics of Intensity of Interdecadal VariationThe intensity of interdecadal variation of urban thermal environment in Nanchang is exceedingly significant. It increases between 0.4℃ to 1.4℃ in the past three decades and it is on an increasing tendency.(3) Seasonal Differences of Urban Thermal EnvironmentExpect for the lower temperature in the summer of 1990s, the city of Nanchang has witnessed the decadal temperature increase in spring, autumn and winter. The most intense thermal environment occurs in the seasons of autumn and winter, and the less intense is in the seasons of summer and spring.(4) Diurnal Variation of the Intensity of Urban Thermal EnvironmentThe diurnal variation of the intensity of urban thermal environment corresponds with the periodic variation of diurnal temperature. It is weak in the morning and in the evening, and the most intense urban thermal environment occurs at noon. It is a unimodal variation.(5) Spatial Distribution of Urban Thermal Environment of NanchangThe downtown temperature of Nanchang is always the highest no matter it is the annual average temperature, the annual highest or the annual lowest, or the temperature distribution in the four seasons. The temperature decreases gradually in the east and west of the city, and the temperature in the west is lower than that of the east because of the mountains of Meiling.2. Causes of Urban Thermal Environment of Nanchang and Its Harms(1) The major causes of the formation of urban thermal environment of Nanchang are the expanding urban area and increasing population, the lack of urban wind porch, the underlying surface which was replaced by asphalt and cement. Massive anthropogenic heat and atmospheric pollution are also responsible for the urban thermal environment of the city. The climatic change of the city is the external factor for the formation of urban thermal environment effect(2) Owing to the thermal environment effect of the city, the record of the extreme heat temperature has been continually set and the duration of it is lengthening. It affects the normal life of the urban residents and their health. The density of near-earth urban pollutants increases due to the existence of the thermal environment effect, causing closure pollution of various types of high concentration pollution sources in the city. Thermal environment effect results in the increasing refrigeration energy consumption and greenhouse gas emissions of the city, which accelerates global warming and thermal environment effect, forming a vicious circle. The growth habit of some plants has changed because of thermal environment effect.3. Correlation Coefficient between Urban Thermal Environment and Green Space Evolution Based on RS and GIS(1) Based on TM remote sensing data and analysis of the thermal field of spatial pattern and its temporal and spatial evolution law of the city, the findings of the research are:the thermal environment effect of the built-up areas of Nanchang is significant in 2003 and 2010. The distribution of thermal environment of the two periods is similar. In 2003, the thermal environment distribution is:there is a high-density thermal environment in the older sections of the city and less in the Changbei district. In 2010, the distribution range of high temperature areas and sub-high temperature areas has decreased significantly. The high temperature spots are gradually distracting, and not as concentrated as they were in 2003(2) Comparing the image maps of urban green space coverage and the distribution of thermal environment in 2003 and 2010, we can draw the following conclusions:the urban green space of Nanchang in 2010 has improved significantly. The greening rate and green coverage rate of every districts of Nanchang are higher than those in 2003. Especially with the city’s "Foresting and Gardening the City and Countryside" project, a large number of high quality urban green space have been built. The increasing urban forest area has changed the distribution of the thermal environment in downtown areas; Through the analysis of the relationship between the greening rate and thermal environment effect of city and the relationship between green coverage rate and thermal environment effect, it can be found that there is a negative correlation between green coverage rate and thermal environment effect. Much more construction of urban green space is an effective way to alleviate thermal environment effect.4. Effect of Thermal Environment on Phenological Period of Plants in Urban Green Space in NanchangBy using the meteorological data of Nanchang and seven common deciduous plants, four evergreen broadleaf plants, and six common coniferous plants that can be easily observed in Nanchang from 2003 to 2012, the research makes the quantative analysis of the relationship between first-flowering date of plants and the temperatures of winter and spring, the relationship between first-flowering date of plants and the average temperature in spring, the relationship between first-flowering date of plants and the average maximum temperature and the average minimum temperature, and the relationship between first-flowering date of plants and the average maximum temperature in Spring. We found that the thermal environment has affected the phenological period of plants in urban green space, and the phenological period of plants has changed because of the urban thermal environment, causing the early phenological period of plants in spring, and the delay of it in autumn.5. Influence of Urban Green Space on Urban Thermal Environment(1) For the alleviation of the urban thermal environment effect, different types of green space shows different effects on the differences of cooling amplitude of the underlying surface. The cooling amplitude in different season is:summer> spring> autumn> winter. The alleviation effect of the environmental effects of urban green space in summer is shown as:water surface> jungle> scarce forest and grassland> grassland> exposed earth> rocky road> cement road.(2) There is a significantly negative correlation between the temperature of urban green space of parks and the area and girth of green space of parks. The temperature decreases with the increase of the area and girth of it. There is a significantly positive correlation between the temperature of urban green space of parks and the ratio of area and girth. The bigger the shape index is, the higher the temper is.There is a relatively weak correlation between the degree of cooling effect on the neighboring environment and different characteristics of green space of parks. The main reason is that the neighboring temperature of the park is influenced not only by the area, girth and shape index of green space of parks, but also by the types of neighboring land, the density of buildings, and the speed and direction of wind. It is the result of mutual superposition and interaction of all sorts of the neighboring environment.(3) For the effect of average temperature and humidity of the city water body of the four seasons, there is an obvious humidifying and cooling effect in spring, summer, autumn. The nearer to the water body, the more obvious the humidifying and cooling effect is. The most obvious effect occurs in summer, while there is no clear difference between spring and autumn. There is a thermal insulation that decreases with the distance away from the water body and humidification effect that increases with the distance away from the water body in winter.(4) The influence of urban green plaques on the neighboring environment is limited when superimposed effect occurs with the presence of multiple urban green plaques. Both the form and layout of the urban green space affect the cooling effect. The role the urban green space system pattern plays in the alleviation of the urban thermal environment effect is very complicated. Based on the previous studies of former researchers, this paper proposes cooling mode of constructing urban green space from the perspective of qualitative research.6. Strategy of Urban Green Space Construction to Alleviate the Urban Thermal Environment EffectsBased on the above conclusions, this dissertation puts forward the strategy of utilizing the urban green space to alleviate the urban thermal environment of Nanchang from the respects of the construction of urban green space system, the popularization of urban vertical planting, the improvement of the quality of urban green space system, the increase and effective use of water and wetland area of Nanchang, and the reasonable city planning.