The Change Characteristics and Trend Prediction of Negative Accumulated Temperature in Gansu Province
甘肃省冬季负积温资源的变化特征及预测

Based on the average daily air temperature data from 80 observatories in Gansu province during the periods of 1966 to 2005,the winter negative accumulated temperature was calculated,the characteristics of its geographical distribution was analyzed,and a spatial model used to estimate the value of small grid where there is no meteorological station was established.It is found that the winter negative accumulated temperature in Gansu is affected by latitude and altitude mainly,and the values vary greatly from northwest to southeast.Using EOF,REOF,and wavelet analysis methods,the abnormal and evolution characteristics of winter negative accumulated temperature in Gansu were analyzed.The results show that the abnormal area can be divided into 5 natural parts,i.e.Hexi corridor,Gannan pasture,Longdong loess plateau,South and East Gansu and Longzhong loess plateau.In the recent 40 years,the winter negative accumulated temperature in Gansu province has been decreasing obviously,and the year 1985 can be regarded as the turning point before which the winter negative accumulated temperature was higher and winters were colder.The 1990s was the decade in which the absolute value of negative accumulated temperature was the smallest.Although all parts of the province have presented the trend of decrease,each part has its own variation characteristics during different periods.Hexi,Longdong and Longzhong started decreasing trend in late 1960s to 1970s,while Gannan started its decreasing trend in late 1950s,and the South and East Gansu started in the middle of 1970s.There is an obvious spatial difference of variation level in Gansu.Each parts has the maximal decreasing level in the 1960s and the 1970s,except for Longnan,the transition belt from semi-tropical climate to temperature zone. The results of wavelet analysis shown that winter negative accumulated temperature presented a periodic fluctuation in different parts of the province.The variation of winter negative accumulated temperature experienced 4 periods at the longer time scale.At last,a forecasting model of negative accumulated temperature for Gansu province was formulated.The predicted values can be computed by using the forecasting models for different parts based on which the situations of cooling and warming in winter from 1966 to 2000 were fitted.The fit accuracy is between 63 percent and 94 percent,and the average accuracy is 79.5 per cent.Using the predicted value to estimate the situations of cooling and warming in winter from 2000 to 2005,the accuracy is between 60 percent and 100 percent,and the average accuracy is 80 per cent.The situations of cooling and warming of winter from 2006 to 2010 were also predicted,which showed that the coming 5 years will be green winter.