Analysis on feature of extreme temperature change in Ningxia in recent 40 years

Using the extreme high and low monthly temperatures of 20 stations in Ningxia during 1961-2004,the basic features of the extreme temperature change were analyzed with climate trend index and Mann-Kendall mutation test.Results showed that,the annual extreme high and low temperatures during this period rose with fluctuation,and the rising range of annual extreme low temperature exceeded that of extreme high temperature;the extreme high and low temperatures of every season changed non-symmetrily,the rising range of extreme high temperatures in autumn exceeded that of extreme low temperatures,the increase of extreme low temperatures in spring,summer and winter were much more obvious than that of extreme high temperatures,and this feature was much more distinct in summer;the monthly extreme low temperatures showed a tendency of increase,the increase of monthly extreme low temperatures exceeded that of extreme high except April,November and December.The study indicated that the scopes of temperature change were decreasing in recent 40 years except in April,November and December,and the extreme temperatures tended to mitigation.