Variation Characteristics of Degree-days and Trend Analysis in Mianyang

Since the 1950s,the degree- days has been the comprehensive evaluation indicator between the climate change and the heating. This paper,based on the background of global warming,using the lowest temperature and the highest temperature data from 1946 to 2005( a total of 49 years),analyzes the degree- days' variation characteristics and its trends. Results shows that: the heating degree- days has the minimum value in the 1998,which is smaller 93. 5% than the maximum value in the 1976,and the average of 10 year's the heating degree- days has the trend of quadratic curve. Cooling degree- days has volatile characters,1960 ~ 1979's cooling degree- days floats at about 1500 ℃·d,1979 ~ 1990's cooling degree- days floats at about 1400 ℃·d,and the cooling degree- days almost is above 1500℃·d after the 1990. The average of 10 year's cooling degree- days fits to the cubic trend curve. Testing the heating and cooling degree- days based on the Mann- Kendall( M- K) test,under α = 0.05 level,the study founds that: the heating degree- days decreases significantly,and mutations start in the 1992,cooling degree- days grows in fluctuation,and mutates from the 1997.