中国西北干旱区降雪和极端降雪变化特征及未来趋势

降雪是中国西北干旱区水文系统中关键的组成要素， 同时也是对气候变化极为敏感的因子。利用中国西北干旱区的89个气象站点逐日气象资料结合IPCC-CMIP5气候情景数据， 研究了该区域降雪和极端降雪的时空变化特征， 并分析了其对气候变化的响应机理及未来变化趋势。结果表明： 1971—2010年， 我国西北干旱区年降雪量显著增加， 但降雪次数却明显减少； 年极端降雪发生次数占总降雪次数的比例不足3%， 但其对年降雪量的平均贡献可达1/4， 且极端降雪量和发生次数的增加是近40年西北干旱区降雪总量增加的主要原因。极端降雪发生时的气温要比非极端降雪发生时的气温平均高3.3 ℃； 当气温在1 ℃以下， 降雪强度随气温升高而增大， 该变化特征基本符合克劳修斯-克拉伯龙方程理论， 气候变暖是导致极端降雪显著增加的主要原因。在RCP4.5气候情景下， 我国西北干旱区未来年降雪次数将大幅减少， 年降雪量将在（2040±5）年前后达到峰值随后下降， 年极端降雪量和发生次数预计（2060±5）年左右达到峰值； 相比基准期， 2050s西北干旱区所有站点的年降雪发生次数都将明显减少， 区域平均年降雪量将减少5%， 而年极端降雪量和发生次数有微弱的增加， 分别增加约2%和4%。

The change features and future trend of snowfall and extreme snowfall in the arid areas of Northwest China

Snowfall is a critical part of the hydrological system and strongly impacted by climate change in the arid areas of Northwest China. This study uses the daily meteorological observations of 89 stations and IPCC-CMIP5 climate scenario data to estimate historical spatial-temporal variations of snowfall and extreme snowfall， mechanisms of response to climate change and future change trend across the arid areas of Northwest China. The results indicated that the annual snowfall amount shows a significant increasing trend， although the obvious decline in occurrences of snowfall during past 40 years （1971—2010）. The occurrences of extreme snowfall only accounts for smaller than 3% of that of snowfall， while contribution of extreme snowfall to annual snowfall amount accounted as high as 25%. And the increases in amount and occurrences of extreme snowfall were considered to be the main causes of the increase in annual snowfall amount. The significantly warmer temperatures （3.3 ℃） for snowfall extremes compared to other snowfall event were observed in the arid areas of Northwest China. And the mean snowfall intensity is expected to increase as temperatures when the air temperature is below 1 ℃ according to the Clausius-Clapeyron relationship. So the climate warming was considered to be the main course of the increase in extreme snowfall. The projected result indicates large reductions in the ensemble mean of occurrences of snowfall across the arid areas of Northwest China under RCP4.5 climate scenario. The annual snowfall amount will reach its tipping point at （2040±5）， while the amount and occurrences of extreme snowfall will reach their tipping point at （2060±5）. By the mid-21st century （2050s）， declines in occurrences of snowfall were projected for all stations. The mean annual snowfall amount is predicted to decrease by 5%， while the amount and occurrences of extreme snowfall have slight increases of 2% and 4% compared with the baseline period， respectively.