Regional trends in recent temperature indices in China

Regional trends in recent temperature indices in China were analyzed from daily surface air temperature maxima and minima at about 498 stations during 1961 to 2000. Some indices based on percentile and those modified by previous studies were used, and linear trends were analyzed for different regions in this study. Results show significant changes in important temperature indices over the past 40 yr, especially in northern China, the Yangtze River valleys and Xinjiang. Trends of decreasing diurnal temperature range were found in mainland China as a whole during 1961 to 2000, with stronger decreases in Northeast China, central South China and the Xinjiang region. There is a trend of cool days significantly decreasing in the middle latitudes near 40degreesC along the Yellow River valley. There are trends of increasing warm days in the upper-middle Yellow River valley and other regions such as along the coast of South China, while there are decreasing trends scattered in the central part of East China. The number of frost days decreased significantly in most of mainland China. Consecutive warm days significantly increased in northern China, while consecutive cold days decreased largely in Xinjiang, the Yellow River valley, the southern part of northeast China, and along the southeast coast of the country. In examining the seasonal contribution, cool nights largely decreased in winter as a whole and the linear trend is about -2.5 to -5 d/10 yr. Another contribution of cool nights comes from summer except for the region of the mid-low Yangtze River valley. The contribution of warm days is attributed to the higher temperature in winter over northern China and in summer over western China and along the coast of South China but a decreasing trend is noted in the basins of the Yangtze and Huaihe Rivers. These trends of temperature indices may be caused by climate factors, such as more rainfall in the Yangtze River basin and dry climate along the Yellow River valley, and non-climate factors, such as urbanization and industrial aerosols.