西北干旱区极端气候水文事件特征分析

Characteristics of extreme climatic/hydrological events in the arid region of northwestern China

中国西北干旱区是对全球变化响应最敏感地区之一。气候变化导致气候水文系统的不稳定性加剧,极端气候水文事件的频度和强度增大、重现期缩短,灾害程度加重。借助资料分析和文献阅读,对过去50 a中国西北干旱区极端气候/水文事件的发生规律、影响机制及未来趋势进行了梳理总结,主要结论如下:(1)西北干旱区的极端气候/水文事件呈逐年增加趋势,特别是20世纪70年代以来增加显著;气温和降水极值都表现为一致的增强趋势。降水量的增多是降雨频率和强度共同增加的结果。(2)中国西北干旱区低温、降水极值在1986年左右发生了明显的突变,高温极值在1996年左右发生突变。突变后,气温和降水极值均发生了显著增强变化。(3)北半球极涡面积指数和青藏高原指数对西北干旱区气候极值变化具有重要影响,冬季极值还受冬季北极涛动和北大西洋涛动等影响。(4)新疆地区有变暖湿趋势,而河西走廊东部则为变干趋势。强大的西伯利亚高压和增强的贝加尔湖气流造成新疆地区降水增加,而河西走廊干旱增加是由东亚夏季风减弱引起的。

The arid region of northwestern China is one of the most sensitive areas to climate change. Climate change have increased the instability of hydrological climate system,resulted in increasing frequency and intensity of climate extremes,as well as shortern the return periods. This paper systematically reviewed the occurrence characteristics,mechanisms and future trends of the extreme climatic/hydrological events in the arid region of northwestern China. Spatial and temporal distribution of precipitation and temperature extremes were analyzed using the Mann-Kendall trend test. The results show that all temperature extremes showed warming patterns,and most of the stations showed significant trends. Warming trends of indices derived from daily minimum temperature were of greater magnitudes than those from maximum temperature,and stations along the Tianshan Mountain had larger trend magnitudes. The number of rainy days had significantly increased. Meanwhile,the precipitation intensity had also significantly increased,which suggested that the increased precipitation in the arid region of northwestern China was due to the increase in both precipitation frequency and intensity. The frequency of extreme hydrological events,such as hail,snowstorm,debris flow,also exhibited an obvious increasing trend,particularly since 1970 s. Based on the general circulation models（GCMs）,the warm extremes will exhibit increasing trends,while the cold extremes will continue to decrease in intensity,magnitude and duration. However,the simulated results derived from GCMs possess large uncertainties,which lead to larger simulated error in the model-predicted extremes than that in mean variability. The relationships between climate extreme trends and elevation were also discussed,and the suggestion of elevation dependency could be misleading in the arid region of northwestern China. Except for linear trends,another change charactersitic for time series is abrupt change. Results indicate abrupt changes in both cold temperature and precipitation extremes occurred in 1986,while the warm temperature extremes was observed in 1996. The temperature and precipitation extremes had significant change after the abrupt change year. Additionally,teleconnection analysis shows that Northern Hemisphere polar vortex area and Tibetan Plateau High were probably the important factors for changes in both temperature and precipitation extremes in the arid region of northwestern China;extremes in winter were also affected by winter Arctic Oscillation and North Atlantic Oscillation. The general evolution of drought was obtained by rotated empirical orthogonal function,as a result,three drought-related spatial patterns were observed,named North Xinjiang,South Xinjiang,and Hexi Corridor,respectively.The North Xinjiang and South Xinjiang revealed wetter trend,while Hexi Corridor showed a dryer trend. The drying trend over the Hexi Corridor was resulted from a weaker Eastern Asian summer monsoon;whereas,a strong Siberian high-pressure and enhanced airflow from the Baikal Lake resulted in increased precipitation in the Xinjiang regions. This paper is a summary of the current researches,which can provide basis for the in-deep study of climate extremes in the arid region of northwestern China.