Analysis Of Climate Change Within Major Urban Area And Its Causes In Beijing-Tianjin-Hebei Region

Using observed daily data of average temperature and the precipitation from 1960 to 2013 in 23 cities meteorological site within Beijing-Tianjin-hebei region of China, this study combined with the monthly NCEP/NCAR reanalysis data and China City Statistical Yearbook. Using method of trend analysis, the Mann-Kendall test, t test, wavelet transform and R/S analysis, this study analysis the variation and the cause of temperature and precipitation changes for the major cities in Beijing-Tianjin-hebei region of China. The main findings are as follows.In recent 54 years, the annual average temperature in Beijing-Tianjin-hebei region was rising, and the spatial distribution of annual mean temperature in the south was higher than that in the north. Spring was the most obvious season of the warming, following the winter and autumn. Spring gave the largest contribution to annual average temperature, following the winter and autumn. The annual mean temperature appeared the periods of 2-4yr,4-6yr and 16yr, and an abrupt climate change was discovered around 1987. The abrupt climate change of spring and winter temperature was discovered around 1992 and 1986. In metropolis, the average temperature, low temperature and high temperature were significantly higher than the temperature of the medium and small cities.the TN10 days showed a decrease trend but the TX10 days had no significant trends; The TN90 days showed increasing trend and TX90 days were increased in most parts of the region. The frequency of extreme high temperature increased and the frequency of extreme low temperature decreased. The trend of extreme low temperature changed faster than that of extreme high temperature. The events of extreme low temperature appeared the periods of 2-4yr and 16yr and the events of extreme high temperature appeared the periods of 2-4yr,6-8yr and 16yr.The annual precipitation of the Beijing-Tianjin-Hebei region showed larger amount of that over the south and west, while the days of precipitation in southeast areas were less than that in the northern. The average precipitation in metropolis was significantly higher than the temperature of the medium and small cities. The precipitation was uneven distributed during a year. It grew from January and reached the maximum in July, then decreased until December. Summer had the most precipitation and winter had the least. The annual precipitation appeared the periods of 2-4yr,8yr and 16yr. There was a decreasing tendency for the extreme precipitation and the intensity of extreme precipitation, as well as the proportion of extreme precipitation decreased. The extreme precipitation days had no significant trends. There was an abrupt climate change of extreme precipitation during 1996.The adjustment of atmospheric circulation on East Asia has a significant effect on the change of extreme temperature of Beijing-Tianjin-Hebei region. When the North China was in the control of cold low pressure of atmosphere, trough of the low pressure brought the strong cold northwest airflow to the Beijing-Tianjin-Hebei region, that was conductive to the formation of extreme low temperature events in the region and extreme high temperature evens was difficult to happen. Otherwise, when the North China was in the control of warm high pressure of atmosphere, the frequency of extreme high temperature events would increase and extreme low temperature was difficult to form in Beijing-Tianjin-Hebei region due to the ridge of warm high atmosphere cut down the cold airflow from the Arctic polar. The seasonal adjustment of the atmospheric circulation in Eastern Asia has a significant effect on the change of the extreme precipitation in Beijing-Tianjin-Hebei region. In summer, when the mean geopotential height anomaly field shows negative(positive) anomalies in the middle-high latitude area of Eastern Asia, the extreme precipitation of the Beijing-Tianjin-Hebei region is more(less) than normal; The amount of extreme precipitation goes larger(smaller) with stronger(weaker) India monsoon, East Asian monsoon and the cyclonic circulation in the Mongolian area in summer; A large(small) intensity of the meridional transportation of.water vapor in summer in the Eastern Asia and the zonal 45 transportation of water vapor in the middle-high latitude area can lead to a large(small) amount of extreme precipitation in Beijing-Tianjin-Hebei region.Human factors have significant relationship with the temperature variation within major urban area in Beijing-Tianjin-Hebei region. Improvement level of urbanization has led to an increase of non-agricultural population. Population growth leads to an increase in anthropogenic heat and urban pollution, while changing the surface of the city, affecting the transport of heat and moisture, changing the regional climate.