基于日SPEI的近55 a西南地区极端干旱事件时空演变特征

利用1960~2014年中国西南地区141个气象台站的逐日气象资料,引入一个新的干旱指数——逐日标准化降水蒸散指数（日SPEI）,对极端干旱事件的年代际、年际、季节内变化及持续性特征进行了分析,结果表明：空间上,近55 a西南春季和年极端干旱程度呈一致的减弱趋势,重庆、四川与贵州的交界处及四川西北部极端干旱程度明显缓解,而夏、秋两季极端干旱表现出增强的趋势并有一定的区域性特征。时间上,春季和全年极端干旱频率、强度和持续天数逐渐减少,春季极端干旱的减弱程度较全年明显;夏、秋两季极端干旱频率、强度和持续天数呈增加趋势,夏季极端干旱的加重趋势比秋季明显。从极端干旱事件的持续性来看,20世纪60年代和21世纪初（2000~2014年）西南遭受的极端干旱最严重,持续期达60 d以上的站点分别占到站点总数的60%和73%。

Spatial-temporal Variability Characteristics of Extreme Drought Events Based on Daily SPEI in the Southwest China in Recent 55 Years

The quantification of drought frequency, duration, intensity, and changes in areal-extent over time is not only essential in the drought risk management making process, but also combat of extreme drought hazard making. However, the current common drought indices can only identify average drought severity over a drought period and cannot indentify drought characteristics at short time scales. The climatic condition in southwestern China, largely an agricultural region, has been considerably variable in the past several decades. Drought has occurred more frequently and has become one of the most serious hazards in the last and current century in Southwest China. The extreme drought events frequently occur, as drought events have taken place in Southwest China. The present study aims to assess the changes in Southwest China's extreme drought events in 1960-2014. Using daily meteorological data collected from 141 stations across the Southwest China from 1960 to 2014, the daily Standardized Precipitation Evapotranspiration Index(daily SPEI) is developed based on daily meteorological data in this study. Latency evaporation is calculated by Penman-Monteith method, from inter-decadal, inter-annual, inter-seasonal variability, persistent characteristic of extreme drought events analyzed over Southwest China in past 55 years by daily SPEI index. The results showed that: From the point of view of space trends to see, it displayed consistent decreased extreme drought trend in spring and whole year over Southwest China in past 55 years. The Chongqing, on the border between Sichuan and Guizhou, northwest of Sichuan are the areas in which severity of extreme drought events has significantly decreased in the past 55 years. But it displayed increased extreme drought trend along with regional extreme drought trend feature in summer and autumn. The frequency, intensity and duration of extreme drought events have significantly increased on the border among of Sichuan, Guizhou, Yunnan, and Chongqing in summer and autumn. From the point of view of time evolution to see, frequency, intensity, duration of extreme drought events is decreasing in spring and whole year, and frequency, intensity, duration of extreme drought events is growing in summer and autumn over Southwest China in past 55 years. The tendency rates of frequency, intensity, duration are -0.01, -0.3, -0.18 d per decades in whole year. The frequency, intensity, duration of extreme drought events in spring showed decreasing trends at rates of -0.02, -1.15,-0.45 d per decades. The intensity, duration of extreme drought events in summer have increased by 0.5, 0.14 d per decades, respectively. The frequency, intensity, duration of extreme drought events in autumn showed increasing trends at rates of -0.01, 0.36, 0.1d per decades. By comparison, spring extreme drought lessen trend is evident than that of whole year, summer extreme drought is stronger than autumn. As a whole, extreme drought degree is strongest in summer, but it is weakest in spring. From inter-decadal scales of view of extreme drought events to see, the severity of extreme drought events was higher in 1960-1969 and in 2000-2014 during the past 55 years. From the point of view of persistent characteristic to see, duration of persistent drought event is longest in 1960-1969 and in 2000-2014 during 1960-2014. Of the two stages, about 60% and 73% meteorological stations have suffered extreme drought lasting more than 60 days.