Comparison About The Influence Of Urbanization On Urban Climate Along The Downstream Of Yangtze River

This paper analyzed the trends of urban climate and that was influenced by urbanization in Anqing, Wuhu, Nanjing and Nantong along the downstream of Yangtze River based on data of annual and monthly mean-temperature, maximum and minimum mean-temperature, mean relative-humidity, mean wind-speed, and precipitation from 1961~2008. There was 18 stations in all, and three or four reference stations around each urban station. And this paper selected some urbanization indicators which were used to measure the comprehensive level of urbanization, which was called urban development index. Models about the relationship between urban climate and urban development index were made.Research results show that:1. The annual mean-temperature, maximal and minimum mean-temperature are all on upward trends, and the rising rate of minimum mean- temperature is the fastest in recent four or five decades. The rising rate of annual mean-temperature is faster with the urban scale extending of different cities, and it is seen as following: megalopolis >large city>medium city. The rising rate of maximum mean-temperature of the large city is faster than medium city and megalopolis. The rising rate of annual minimum mean-temperature is slower with the urban scale extending of different cities.The intensities of heat island effect about annual mean-temperature, maximal and minimum mean-temperature of four cities are increasing except annual maximal mean-temperature of Nanjing. The intensity of heat island effect about annual mean-temperature is that medium city is fastest, and megalopolis is the slowest. The intensity of heat island effect about annual maximal mean-temperature is that large city is fastest, and megalopolis is the slowest. The intensity of heat island effect about annual minimum mean-temperature is that megalopolis is fastest, and medium city is the slowest.The temperatures in Spring, Autumn and Winter are increasing prominently along the downstream of Yangtze River. Through the comparison of the increasing speeds of the intensity of urban heat island in four seasons of the four cities, the contribution rate of Summer is the biggest to the urban heat island in Anqing which represents the medium city, the contribution rate of Autumn is the biggest to the urban heat island in Wuhu, Nantong which represent the large city, and Nanjing which presents megalopolis.2. The annual mean relative-humidity is decreasing along the downstream of Yangtze River, and the decreasing speed becomes faster with the city scale extending. There are dry island effects in all four cities, though the trends are inconspicuous. The seasonal relative-humidity of four cities is decreasing, too. Though the significance is not high, there are dry island effects, and the intensities of them are increasing. The intensity trends of seasonal dried island effects are in accordance with that of annum.3. The annual and seasonal mean wind-speeds are decreasing obviously with the development of the urbanization along the downstream of Yangtze River. The decrease range of annual mean wind-speed is biggest in Wuhu and Nanjing, and that in Nantong is the smallest. The decrease ranges of summer wind-speed in four cities are the smallest, and that of autumn wind-speed in Wuhu, Wuhu and Nanjing are the biggest, and that of winter wind-speed in Nantong is the biggest.4. The trends of annual precipitation are all insignificant in recent 48 year of four cities. The trends of Anqing, Nanjing and Nantong are increasing since not obviously, and it is fluctuating in Wuhu. The trends and range of precipitation influenced by urbanization between annual and flood-season are coincident.5. The characteristics of impacts that the development of cities on the urban climate are not entirely conforming to Kuznets curve. The intensities of heat island effect about annual and minimum mean-temperatures are rising first, and then falling off, which conform to Kuznets curve to a certain extent. Although that of maximal mean-temperatures are also rising, the significance are insignificant. The trends of annual mean relative-humidity are weakly rising in the later period, and that of annual mean wind-speed are obviously decreasing with the development of the cities, and the two are not conformed to Kuznets curve.6. The trends of intensities of heat island effect about annual, maximum and minimum mean-temperatures in Anqing, Wuhu and Nanjing are in accordance with Kuznets curve except Nantong. The trends of that in Nantong are rising with the development of urbanization in the later period.7. The relationship models between annual mean relative-humidity and urbanization are significant except that of Nanjing. Only that trend in Nantong is in accordance with Kuznets curve. The trends of mean relative-humidity in Anqing and Wuhu are rising in the later period, and which in Nanjing is gradually decreasing with urbanization.8. The relationship models between annual mean wind-speed and urbanization are all significant. The trends of annual mean wind-speed with urbanization in Nantong and Nanjing are rising first, and decreasing then, which conform to Kuznets curve. And that in Anqing and Wuhu are decreasing first, and rising then, but that in Wuhu is rising insignificant in the later period.