Temporal Change of Warm Winter Events over the Last 56 Years in China

The climate of China is now clearly in the global warming up trend, in which the winter warming of thenorthern China is the most obvious.The influence of the warm winter upon the human society is omnibearing, including the direct or indirect impact on human health, daily life, economy activity, agriculture product and ecological environment.Generally, the warm winter means that the air temperature of winter is higher than the climatenormal values (the winter air temperature climatology value from 1971 to 2000).According to the China nationalstandard, the warm winter is classified into two groups by space and intensity grades.In the space group the warmwinter is divided into three spatial grads as sing le station warm winter, regional warm winter, and national warmwinter.In the intensity group, there are two grades as weak warm winter (warm winter) and strong warm winter.Average winter air temperature is divided into 3 probability categories to define the threshold of warm winter forsingle station and its warm winter intensity.Then the division criterions for regional and national winter warm intensity are calculated according to percentile rank of warm winter stations and areas respectively.On the basis of the new division method for warm winter, the characteristics of warm winter since 1952 in China are analyzed too.The analysis reveals that the southern China has a higher frequency of warm winter than northern China, while inmid-west China region strong warm winter occurs more frequently.The rising amplitude of warm winter index islarger in northern China than that in southern part, indicating that the warming trend in northern China is moreobvious.During 1952 to 1985, the occurrence of warm winter is rare in the nation-wide of China, when the frequency of warm winter in southern part of China is slightly higher than that happens in the northern part of China.The incidence of warm winter changes from the year of 1986.The number of warm winter year increases since1986 both in southern and northern China with that of northern part increasing significantly.The results also showthat there are 15 national warm winter years over 56 years with 5 strong warm winters.National warm winter index has an obvious rising trend at a warm winter area rate of 10%per 10 years.However, the air temperature hasgreat year -to-year variations, the possible abnormal cold winter should be properly considered even in the obviousglobal warming trend, and hence impacts of the cold winter shouldn't be neglected.