Study On The Characteristics Of Climate Change In The Hanzhong Basin

Based on the observational data of temperature,precipitation,sunshine hours,extreme maximum temperature and extreme minimum temperature in Hanzhong Basin from 1960 to 2016,linear tendency estimation,wavelet characteristic analysis and Man-Kendall mutation test were used to thoroughly analyse the interannual and seasonal variation trend,multi-time scale variation and changes of the five meteorological elements in Hanzhong Basin.The climatic characteristics of Hanzhong Basin were compared with those of Guanzhong Plain and Chengdu Plain,In general,the trend of the temperature change of Hanzhong basin in recent 57 years is becoming significantly warmer,change in precipitation is more frequent,sunshine hours shows a downward tendency.The main results are as follows:(1)The characteristics of the variation on mean temperature.In the past 57 years,the interannual and seasonal mean temperatures in the study area showed an obvious tendency of warming,especially in spring and winter.There was no obvious period of oscillation in the long time series of annual mean temperature and winter mean temperature,but significant changes have respectively occurred in 2002 and 1999.The long time series of mean temperature in spring,summer and autumn showed that the main oscillation periods to be of 32 a,49a and 29 a,respectively,and significant changes have been separately observed in 2004,2011 and 2007.The annual mean extreme minimum temperature and extreme maximum temperature in the study area have presented a significant trend of warming.The long-time series of annual mean extreme minimum temperature has a main oscillation period of 28 a,but there is no abrupt point of change.The temperature has stayed above the positive critical value since 1996;The long time series of annual mean extreme maximum temperature has a main period of 51 a,and a sudden change occurred in 2008.The temperature has stayed above the threshold since 2012 and is experiencing even more pronounced rise.Among Guanzhong Plain,Hanzhong Basin and Chengdu Plain,Hanzhong Basin has showed the most obvious trend of warming.The extreme temperature in Hanzhong basin displays a significant upward trend,the rising of the temperature in the plain area is relatively slow,and the rise of extreme temperature in the north is more significant than the south.(2)The characteristics of variation on precipitation.In the past 57 years,the annual average precipitation,the spring and autumn mean precipitation have shown a tendency of slowly decreasing,and the main oscillation periods have appeared to be of 24 a,25a and 5a,respectively.The variation trend of the long time series of average precipitation in summer and winter is not found to be obvious,and the main periods of oscillation are respectively 26 a and 13 a.Frequent changes in the average annual and spring precipitation were concentrated in the period of 2013-2016.The frequent abrupt changes in the average summer precipitation were also concentrated in the period of 2013-2016.Frequent abrupt changes in autumn mean precipitation occurred after 1992.Frequent abrupt changes in winter mean precipitation mainly occurred between 1960-1980 and 2008-2016.Guanzhong Plain,Hanzhong Basin and Chengdu Plain together have displayed the characteristics of "Wet South Dry North".(3)The characteristics of variation on sunshine hours.In the past 57 years,the interannual and seasonal mean sunshine hours in the study area showed a downward trend,among them the interannual and winter average sunshine hours had the most significant decrease.The annual,spring,summer,autumn and winter mean sunshine hours have the main oscillation periods of 29 a,30a,26 a,26a,19 a,respectively.The abrupt changes of the mean sunshine hours in the interannual,summer and winter periods occurred in 1981,1980 and 1979,respectively,and were found to be below the critical value around 1983-1984.The average sunshine hours in spring were more abrupt than others,the frequent changes mainly occurred between 1960-1970 and 2000-2016.There were two abrupt spots in autumn mean sunshine time,which occurred in 1984 and 1987,and appeared to be below the critical value after 2005.The decreasing trend of sunshine hours in plain area is larger than that of in basin area.