中国西南地区冻雨灾害特征分析与评估

利用1961-2015年中国西南地区96个气象台站逐日气象观测资料，采用模糊信息分配法分析了我国西南地区出现冻雨天气时有利气象要素的变化规律。选取气温、湿度及日照时间确定了西南地区冻雨天气判断的评估标准：日平均气温≤ 2℃，日最高气温≤ 8℃，日最低气温≤ 0℃，相对湿度≥ 80%，日照时间≤ 1 h。通过重建发现发生冻雨的天数在11月-次年3月间呈现单峰型变化，其季节内冻雨日数的演变规律是少~多~少，每年的1月冻雨日数最多。经检验上述指标可用于重建西南地区各站点冻雨强度指数，并由此评估了西南地区冻雨灾害的时空分布状况。四川盆地南缘、云贵高原大部，以及湖南省东部地区冻雨指数大，表明该区域遭受冻雨灾害严重；青藏高原、川西高原地区气温虽低，但相对湿度小，日照时间长，均不满足冻雨条件，因此发生冻雨灾害的风险小。近年来我国西南地区冻雨强度总体呈现减弱的趋势。

Freezing rain disasters in Southwest China:characteristic analysis and evaluation

Based on daily data from 96 meteorological stations from 1961 through 2015,the meteorological element variations in relation to freezing rain occurred in southwest China were analyzed by using fuzzy information distribution method,in order to establish freezing rain weather assessment indexes.The results show that a comprehensive meteorological threshold condition can be used to assess freezing rain weather,i.e.,the daily average temperature less than or equal to 2 ℃,daily maximum temperature less than or equal to 8 ℃,daily minimum temperature less than or equal to 0 ℃,relative humidity more than or equal to 80％ and sunshine hours less than or equal to 2 hours.The number of days with freezing rain has a unimodal variation from November through March.In the southern margin of Sichuan Basin,the vast majority of Yunnan-Guizhou Plateau and the eastern Hunan Province,there is a high freezing rain index,indicating that there is a serious area suffering from freezing rain.Temperature in the Tibet Plateau and the Western Sichuan Plateau is low,but the relative humidity is small,and the sunshine time is long,which does not meet the conditions of freezing rain.Therefore,the risk of freezing rain is small.In recent years,the intensity of freezing rain in Southwest China has been decreasing.The indexes can be used to reconstruct the freezing rain intensity index sequence in various sites,and thus to evaluate the spatial distribution of freezing rain disaster in Southwest China.