Research on Climate Warming and Urban Heat Island in Xi'an

The length of meteorological records in most weather stations over China is less than 50 years. To do researches on the climate variation on time scale of a hundred years, stations selected are those mainly centralize in big cities with longer records. The fastest growing period of global warming is exactly the rapid city expansion time in China, during which the farmland around the weather stations turned into cities. The urban heat island could lead to the rising temperature, so the variation of temperature in cities is the jointly affected result of urban heat island and climate change. In order to analyze the contributions of each, mean monthly temperature anomaly from 1961 to 2003 in Xi'an (city) and 4 stations around (town) are selected to do contrast analysis. That is to say, the contribution of urban heat island in Xi'an is analyzed on the assumption that it only exists in Xi'an station. Result shows that the average value of mean monthly temperature anomaly from 2000 to 2003 increases 1.55 ℃ more than that from 1961 to 1972, and the average value of the other 4 stations at the same time only increases 0.48 ℃. It indicates that the warming mainly results from the urban heat island, and the climate change warming is minor in Xi'an. In the process of warming, obvious difference between Xi'an and the other 4 stations mainly exists in two periods. It can be reflected perfectly in the moving average curve (36 samples) of mean monthly temperature anomaly distributed according to the time. According to the investigation on urban construction, the two periods are consistent with the time of rapid city expanding towards the meteorological stations. The urban heat island model in Xi'an based on the analysis above is set up, and the cause of the increasing temperature in Xi'an is separated into the city urban heat island and the climate variation respectively. Increasing temperature in Xi'an aroused by urban heat island is 1.07 ℃, and that by climate variation is 0.48 ℃. Balance between mean monthly temperature of Xi'an and the 4 stations around is also analyzed for testifying the result, and the rising range in Xi'an is about 0.93 ℃ higher than the latter. When focusing on the climate warming, the urban heat island raised by change of surrounding environment which is brought by extending of city can not be ignored. Range of rising temperature aroused by urban heat island is larger than that of climate variation. Because the extending time of different city is not the same, corresponding model should be set up separately so as to eliminate the contribution of urban heat island to increasing temperature.