Detection And Comparison Of Effect Of Urbanization On Climate In Three Mega Urban Agglomerations Of China

Beijing-Tianjin-Hebei region, the Yangtze River Delta and the Pearl River Delta region are the three most developed areas in China with the highest urbanization level, so research on the effect of urbanization is of great scientific and practical significance. Based on daily climate data from national base climatological stations in the period of1951-2009and social-economic statistical data such as population, GDP, electricity consumption and urban built-up area in the period of1986-2008, with establishing urbanization index and calculating several climatic indices, the methods of comparing typical cities with regional average, corresponding EOF modes and Granger causality test were used to analyze development trend and spatial distribution pattern of urbanization, climatic effect of urbanization in the three agglomerations and typical cities was also detected and compared.Firstly, times series of population, GDP, electricity consumption and urban built-up area were analyzed, and standard urbanization index was also established using homogenized population data. The results reveal that:since Reform and Opening up, urban development of three agglomerations is continuously enlarging and accelerating, gap between different cities is also narrowing; the first EOF mode of standard urbanization index explicitly depicts spatial distribution pattern of urbanization level and speed, which can be used as urbanization mode.Secondly, urbanized warming rate of8typical cities in three regions was analyzed with the method of comparing typical cities with regional average. The results are as follows:urban temperature raises remarkably under the influence of rapid urban progress, especially during the nighttime, urbanization effect is enhancing in the last30years. Typical cities can be classified into three groups:in the first group, warming is most obvious in cold season and at night, frequency of high temperature is decreasing or shows no obvious trend; for the second group, the intensity of warming is strongest in hot season and midday, extreme high temperature events are also increasing rapidly; the last group experiences most evident warming in transition seasons which are spring and autumn, the increasing extent of high temperature is smaller than that of the second group.After37climatic indices being calculated, regional urbanization effect was detected using method of EOF decomposition and mode corresponding. The conclusions are as follows:the overall effect on climate was strongest in the Yangtze River Delta and weakest in the Pearl River Delta; urbanization effect on precipitation varies among three regions, Beijing-Tianjin-Hebei region becoming drier, and the Yangtze River Delta, the Pearl River Delta becoming more humid. Emphasis was on the characteristics of Beijing-Tianjin-Hebei region and the Yangtze River Delta. In both regions, there are significant increases in daily mean and minimum temperatures, with obvious warming in spring and autumn, while extreme temperature seems unrelated to urbanization. The difference between two regions are in two aspects: warming rate of daily maximum temperature is positive in the Yangtze River Delta, but it’s nearly zero in Beijing-Tianjin-Hebei region; urbanization effect is stronger in summer than in winter for the Yangtze River Delta, however it’s opposite for Beijing-Tianjin-Hebei region.In the next, regional urbanization effect was investigated using Granger causality test. The intensity of urbanization effect is seen as follows:Beijing-Tianjin-Hebei region> the Yangtze River Delta> the Pearl River Delta. There are three common points in Beijing-Tianjin-Hebei region and the Yangtze River Delta:urbanization effect is stronger on temperature than on precipitation; urbanization raises daily mean, maximum and minimum temperature to some extent; climatic effect is most evident in spring and autumn, and the weakest in winter. The different features are in four aspects, such as urbanization effect on precipitation, the relationship between maximum and minimum temperature, urban influence on extreme temperature and the characteristics in summer.Finally, the regional climatic effect of urbanization was compared from two alternative methods. Although they don’t have the same result for every climatic index, two methods are in good consistency as a whole, they are generally convincible to show major characteristic of urbanization effect. The same features are as follows: urbanization remarkably influences temperatures, increases in daily mean, maximum and minimum temperature under rapid urban progress; there is strong urban effect in spring and autumn; in Beijing-Tianjin-Hebei region, increasing in minimum temperature is larger than that in maximum temperature, while they are almost same in the Yangtze River Delta; in Beijing-Tianjin-Hebei region, extreme precipitation weakens, summer and annual precipitation also decreases. In Beijing-Tianjin-Hebei region, diurnal temperature range of summer, winter and the whole year decreases to a certain extent. In addition, a couple of climatic indices which are sensitive to urbanization are sorted out, the number of which is14in Beijing-Tianjin-Hebei region and11in the Yangtze River Delta.