中文摘要：

利用ERA-Interim再分析资料,分析了1979-2014年中国极端通用热气候指数（Universal Thermal Climate Index,UTCI）时空变化特征。结果表明：（1）从全国平均看,暖指数均显著上升,且暖夜日数升幅（1.50 d/10a）大于暖昼日数（1.32 d/10a）,夏季最低UTCI升幅（0.63°C/10a）大于夏季最高UTCI（0.24°C/10a）。暖昼、暖夜日数自90年代初后迅速增多。冷指数中,冬季最高UTCI显著上升（0.42°C/10a）,其他指数无显著趋势。冷昼、冷夜日数阶段性特征明显,20世纪80年代和2000年代中期之后均值、波动幅度均较大,其间均值、波动幅度均较小。最近10年,中国夏季极端热应力和冬季极端冷应力均较为显著。（2）从空间分布上看,暖指数在中国绝大多数区域上升。暖昼、暖夜日数的上升中心均位于新疆东部和内蒙古中部地区,升幅分别为3 d/10a～4.80 d/10a、4 d/10a～5.94 d/10a。冷指数中,冬季最高UTCI在82.04%的区域上升,内蒙古中部和西部及陕西北部地区升幅最大,达1.20°C/10a～2.18°C/10a;其他指数的变化趋势在绝大多数区域不显著,且变化幅度较小。（3）极端UTCI指数和极端气温指数均表明,中国多数地区夏季暖昼、暖夜日数上升,冬季冷昼、冷夜日数下降。但极端气温指数揭示的暖昼、暖夜日数升幅更大,且暖夜日数升幅大于暖昼日数的现象更显著,冷昼、冷夜日数下降趋势的范围和降幅也更大。

英文摘要：

Based on ERA-Interim reanalysis data, this study investigated the spatio-temporal changes in extreme UTCI indices in China during 1979-2014. The results show that national average heat indices have significantly increased. Hot nights （1.50 d/10a） and summer minimum UTCI （0.63 ℃/10a） have larger increasing rates than hot days （1.32 d/10a） and summer maximum UTCI （0.24 ℃/10a）. The number of hot days and hot nights has increased rapidly since the early 1990s. In comparison, most of cold indices show no significant trends, except for winter maximum UTCI （0.42 ~ C/10a）. Cold days and cold nights series show distinct characteristics in different periods, with both high mean values and large fluctuation ranges in the 1980s and the period after the mid-2000s, and both low mean value and small fluctuation range in the period between them. Particularly during recent 10 years, China has been facing both severe extreme heat stress in summer and cold stress in winter. From the perspective of regional differentiation, heat indices increase over most of China. The largest increasing magnitudes of hot days and hot nights were observed over eastem Xinjiang and central Inner Mongolia, namely 3-4.80 d/10a and 4-5.94 d/10a, respectively. Winter maximum UTCI increased at 82.04% of China, with the largest increasing rates （1.20-2.18 ℃/10a） in central and western Inner Mongolia and northern Shaanxi. Other cold indices show no significant trends in most of China, and their changes are relatively small. In addition, the comparison between extreme UTCI indices and extreme temperature indices shows that, both of them reveal increasing hot days and hot nights and decreasing cold days and cold nights in most parts of the country. Nonetheless, the increases in hot days and hot nights indicated by extreme temperature indices have relatively large magnitudes, and the phenomenon of hot nights increasing faster than hot days is more prominent. Besides, decreasing trends in cold days and cold nights show larger magnit