Studies On The Temperature Change In The Last 100 Years Over Zhejiang Province

Using the air temperature data as many as possible with quality control, homogenization and interpolation, the higher-quality air temperature dataset is obtained over Zhejiang province from 1905-2012. To overcome the difficulty of few temperature stations during the early time period for calculating the averaged temperature series over Zhejiang province during the early time period, a new approach named as GAo SV(Global Adjusting of Station Value) is proposed. Then, the temperature change trends in the last 100 years, the variation trends of hot wave and warm winter in the last 60 years, and the spatial difference of temperature rises over Zhejiang are analyzed and discussed. The main conclusion is as follows:1. The construction of meteorological stations in Zhejiang province is very slow at the early time, and then becomes fast but with some fluctuations. From 1904 to 1924, there was only one station at Hangzhou, and two stations at Hangzhou and Wenzhou from 1925 to 1934. Although there were 10 temperature stations in 1935, the observations were often interrupted from 1935 to 1950 due to various reasons, and in certain time only two made the observations. Compared with others stations, the temperature observation data at Hangzhou and Wenzhou stations are much continuous with almost no missing data, so these two stations are main stations for constructing temperature data series ranging from 1905 to 1950.2. The GAo SV method reasonably revises temperature observations at one station based on regional averaged observations, especially for the regions where there were few temperature stations(e.g. one or two). Moreover, the results became more reliable with added stations and spatial coverage. For example, for one station the absolute difference of annual temperature is 0.08℃ between the revised values with GAo SV and averages at all stations, and reduces to 0.03℃ for two stations.3. Based on the 100-year temperature data series, the annual mean temperature over Zhejiang gradually increases with an approximate rise rate of 0.11℃ per decade from 1905 to 2012, and 0.37℃ per decade from 1971 to 2012. The rising trend becomes more obvious from 1980 to 2012 with a approximate rise of 0.51℃ per decade. In the last 100 years, the lowest annual mean temperature over Zhejiang is in 1917, the highest is in 2007, and the warmest decade appeares in the first decade of 20 th century. Analogous to the whole country, there are two obvious warming periods, respectively, from 1905 to 1942 and from 1985 to about 2005, but the warming trend over Zhejiang is more remarkable, especially since 1980 s with the warming rate over Zhejiang(0.51℃ per decade) distinctly higher than that over the whole country(0.38℃ per decade).4. Although the annual mean temperatures at each county or city in Zhejiang all show warming trends from 1951 to 2012(especially 1971 to 2012), the warming amplitudes are different among different regions. The warming rate in the northern part of Zhejiang is higher than that in the southern part, and warming rate near the coast areas is higher than that in inland mountain areas. The region with the highest warming rate(0.57℃ per decade) lies in Yinzhou, and the lowest warming rate(0.19℃ per decade) lies in Yunhe.5. Under the background of global warming, the occurrence frequencies of hot wave day and warm winter in Zhejiang increase in the last 60 years. Since 1980 s, the number of hot wave days has a increasing trend, especially after 2000. In 2003, the number of hot wave days is 42.5 d, which is the maximum in the last 60 years. The variation of winter mean temperature is relatively stable before 1990, but after that the winter mean temperature generally increases. According to the criterion of mean winter temperature during 1981 to 2010, there are 6 warm winters in 50 years before 2000, but 7 warm winters from 2000 to 2012.6. Using wavelet and power spectrum analysis technique, the multi-time scale character for temperature change in the last 100 years in Zhejiang are analyzed. The results indicate that there are oscillation periods of 10-20 years, 30-45 years, and more than 50 years in the 100-year temperature dataset in Zhejiang. Moreover, the oscillation period of 30-45 years is diagnosed out by both wavelet analysis and power spectrum analysis. The wavelet analysis shows that Zhejiang experiences two warming courses for the timescale of more than 50 years, respectively before 1940(weak) and after 1950(strong), three warming periods and three cooling periods for the 30-45-years timescales with the warming periods occurred respectively in 1910-1940, 1980-2007 and 1950-1960(weak).