Orginal Article
1. 忻州师范学院地理系,山西 忻州 0340002. 西北师范大学地理与环境科学学院,甘肃 兰州 730070
1. Department of Geography, Xinzhou Normal University, Xinzhou 034000, Shanxi, China2. College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, Gansu, China
中图分类号:S166
文献标识码:A
文章编号:1000-0690(2018)03-0474-10
版权声明:2018 《地理科学》编辑部 本文是开放获取期刊文献，在以下情况下可以自由使用：学术研究、学术交流、科研教学等，但不允许用于商业目的.
基金资助:国家自然科学基金项目（41561024）、山西省高等学校哲学社会科学研究项目（2015265）资助National Natural Science Foundation of China (41561024), Philosophy Social Science Research Project of Shanxi Colleges and Universities (2015265).
作者简介:
展开
摘要
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%。
关键词：极端干旱事件;日SPEI;中国西南
Abstract
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.
Keywords：extreme drought events;daily SPEI;the Southwest China
图1 西南地区气象站点分布
Fig.1 The location of meteorology stations in the Southwest China
1.3.1 日SPEI计算
1.3.1 日SPEI计算
本研究对SPEI指标做了改进,改进后的日SPEI干旱指数计算过程与月SPEI类似,具体计算步骤如下：
本研究对SPEI指标做了改进,改进后的日SPEI干旱指数计算过程与月SPEI类似,具体计算步骤如下：
1）计算逐日潜在蒸散（ET0）。采用FAO-56（1998）推荐的Penman-Monteith模型计算：
1）计算逐日潜在蒸散（ET0）。采用FAO-56（1998）推荐的Penman-Monteith模型计算：
式中：ET0为日潜在蒸散量,mm;Δ为温度随饱和水汽压变化的斜率,kPa/℃;U2为离地2 m高处风速,m/s;ea为空气饱和水汽压,kPa;ed为空气实际水汽压,kPa;T为平均气温,℃;r为湿度表常数,kPa/℃;Rn为到达地面的净辐射,MJ/(m2d);G为土壤热通量密度,MJ/(m2d)。
式中：ET0为日潜在蒸散量,mm;Δ为温度随饱和水汽压变化的斜率,kPa/℃;U2为离地2 m高处风速,m/s;ea为空气饱和水汽压,kPa;ed为空气实际水汽压,kPa;T为平均气温,℃;r为湿度表常数,kPa/℃;Rn为到达地面的净辐射,MJ/(m2d);G为土壤热通量密度,MJ/(m2d)。
2） 计算逐日降水量与潜在蒸散的差值:
2） 计算逐日降水量与潜在蒸散的差值:
$\lbrace^{D^{k}_{i,j}=\sum\limits_{i=31-k+j}^{30}D_{i-1}+\sum\limits_{l=1}^{j}D_{i,l} j＜{k}}_ {D^{k}_{i,j}=\sum\limits_{l=j-k+1}^{j}D_{i,l} j\geq{k}}$
$\lbrace^{D^{k}_{i,j}=\sum\limits_{i=31-k+j}^{30}D_{i-1}+\sum\limits_{l=1}^{j}D_{i,l} j＜{k}}_ {D^{k}_{i,j}=\sum\limits_{l=j-k+1}^{j}D_{i,l} j\geq{k}}$
3） 采用了三参数的log-logistic概率分布对Di数据序列进行拟合。
3） 采用了三参数的log-logistic概率分布对Di数据序列进行拟合。
式中：参数a、β、γ分别为尺度、形状及初始状态参数,采用线性矩的方法拟合获得：
式中：参数a、β、γ分别为尺度、形状及初始状态参数,采用线性矩的方法拟合获得：
式中：Γ为阶乘函数,ω0、ω1和ω2为原始数据序列Di的概率加权矩。由此可以得到Di概率密度的累计概率密度函数：
式中：Γ为阶乘函数,ω0、ω1和ω2为原始数据序列Di的概率加权矩。由此可以得到Di概率密度的累计概率密度函数：
当累积概率P≤0.5时,概率加权矩（w）公式为：
当累积概率P≤0.5时,概率加权矩（w）公式为：
式中：c0=2.515 517,c1=0.802 853,c2=0.010 328,d1=1.432 788,d2=0.189 269,d3=0.001 308。
式中：c0=2.515 517,c1=0.802 853,c2=0.010 328,d1=1.432 788,d2=0.189 269,d3=0.001 308。
1.3.2 气象极端干旱过程的确定
1.3.2 气象极端干旱过程的确定
极端干旱事件定义为：当日SPEI指数连续15 d每天的值低于-2时,则为一次极端干旱过程。干旱过程开始日期为第1天SPEI值达到极端干旱等级以上的日期,结束日期为最后一天SPEI指数为无极端干旱的日期,当SPEI指数连续5 d为无旱等级时极端干旱过程结束。极端干旱过程开始到结束的天数为干旱持续时间。过程内各日SPEI指数绝对值之和,表示极端干旱过程的强度,其值越大干旱程度越强。
极端干旱事件定义为：当日SPEI指数连续15 d每天的值低于-2时,则为一次极端干旱过程。干旱过程开始日期为第1天SPEI值达到极端干旱等级以上的日期,结束日期为最后一天SPEI指数为无极端干旱的日期,当SPEI指数连续5 d为无旱等级时极端干旱过程结束。极端干旱过程开始到结束的天数为干旱持续时间。过程内各日SPEI指数绝对值之和,表示极端干旱过程的强度,其值越大干旱程度越强。
1.3.3 Mann-Kendall趋势检验法
1.3.3 Mann-Kendall趋势检验法
采用Mann-Kendall（M-K）趋势检验方法对西南141个气象站极端干旱事件的变化趋势进行显著性检验。M-K趋势检验是非参数统计检验方法,计算简单,是目前水文学中常用的趋势诊断方法。M-K趋势系数小于0表示时间序列呈下降趋势;反之,则表示时间序列呈上升趋势;并且趋势系数的绝对值大于1.96时,表明变化趋势通过0.05的显著性水平检验。
采用Mann-Kendall（M-K）趋势检验方法对西南141个气象站极端干旱事件的变化趋势进行显著性检验。M-K趋势检验是非参数统计检验方法,计算简单,是目前水文学中常用的趋势诊断方法。M-K趋势系数小于0表示时间序列呈下降趋势;反之,则表示时间序列呈上升趋势;并且趋势系数的绝对值大于1.96时,表明变化趋势通过0.05的显著性水平检验。
图2 1960~2014年西南地区春、夏、秋及年极端干旱频率、强度和持续天数趋势系数空间分布
Fig.2 Spatial trend of extreme drought frequency, intensity, duration in spring, summer, autumn and annual time scales in the Southwest China from 1960 to 2014
2.2.1 极端干旱事件年际演变
2.2.1 极端干旱事件年际演变
图3 西南地区极端干旱事件频率、强度和持续天数的年际演变
Fig.3 Inter annual variation of extreme drought frequency, intensity and duration in the Southwest China
2.2.2 极端干旱事件的年代际演变
2.2.2 极端干旱事件的年代际演变
表1 1960~2014年西南地区极端干旱事件特征年代际变化
Table 1 Decadal variation of extreme drought characteristics in the Southwest China from 1960 to 2014
图4 西南地区各年代极端干旱事件持续天数的空间分布
Fig.4 Spatial distribution of extreme drought duration in the Southwest China
Table 2 Top 15 extreme drought events ranked by duration in the Southwest China from 1960 to 2014
1） 近55 a来西南年及春季极端干旱频率、强度和持续天数呈减少趋势且空间分布基本一致,重庆、四川与贵州的交界处以及四川西北部极端干旱程度明显缓解,西南东北部极端干旱程度明显增强。夏、秋两季大部分区域极端干旱程度呈增强趋势,重庆、四川和贵州交界处附近区域极端干旱事件频率、强度和持续天数增加趋势较明显。
1） 近55 a来西南年及春季极端干旱频率、强度和持续天数呈减少趋势且空间分布基本一致,重庆、四川与贵州的交界处以及四川西北部极端干旱程度明显缓解,西南东北部极端干旱程度明显增强。夏、秋两季大部分区域极端干旱程度呈增强趋势,重庆、四川和贵州交界处附近区域极端干旱事件频率、强度和持续天数增加趋势较明显。
2） 年尺度上,近55 a来西南春季和年极端干旱事件频率、强度和持续天数均呈减少趋势,春季极端干旱减少趋势更明显;夏、秋两季极端干旱事件频率、强度和持续天数处于增加趋势,夏季增加幅度较大。年代际尺度上,20世纪60年代和21世纪初（2000~2014）是西南年及春、夏、秋三季极端干旱程度较严重的阶段。
2） 年尺度上,近55 a来西南春季和年极端干旱事件频率、强度和持续天数均呈减少趋势,春季极端干旱减少趋势更明显;夏、秋两季极端干旱事件频率、强度和持续天数处于增加趋势,夏季增加幅度较大。年代际尺度上,20世纪60年代和21世纪初（2000~2014）是西南年及春、夏、秋三季极端干旱程度较严重的阶段。
3） 近55 a来,西南极端干旱事件的持续天数经历了先减少后增加的变化。21世纪初（2000~2014年）西南地区遭受的极端干旱最严重,73%的站点极端干旱持续期达到60 d以上;20世纪60年代次之,60%的站点极端干旱持续期达60 d以上。
3） 近55 a来,西南极端干旱事件的持续天数经历了先减少后增加的变化。21世纪初（2000~2014年）西南地区遭受的极端干旱最严重,73%的站点极端干旱持续期达到60 d以上;20世纪60年代次之,60%的站点极端干旱持续期达60 d以上。
The authors have declared that no competing interests exist.
The authors have declared that no competing interests exist.
2009年秋至2010年春我国西南地区严重干旱的成因分析
Analyses of the causes of severe drought occurring in Southwest China from the fall of 2009 to the spring of 2010
变化环境下我国干旱灾害的综合应对
Reflections on integrated coping strategies for drought in China in changing environment
西南地区近年特大干旱灾害的启示与对策
Revelation and countermeasures of catastrophic drought disasters in recent years in Southwest China
近60年中国西南地区干旱灾害规律与成因
Characteristics and origins of drought disasters in Southwest China in nearly 60 years
区域农业干旱风险评估研究——以中国西南地区为例
Drought risk assessment on regional agriculture: A case in Southwest China
2009-2011年我国西南地区旱灾程度及其对植被净初级生产力的影响
Drought in southwestern China and its impact on the net primary productivity of vegetation from 2009-2011
基于SPEI的西南地区近53a干旱时空特征分析
Temporal and spatial distributions of drought in Southwest China over the past 53 years based on Standardized Precipitation Evapotranspiration Index
基于湿润指数的1960-2011年中国西南地区地表干湿变化特征
Characteristics of southwestern China dry-wet condition based on wetness index in 1960-2011
基于相对湿润度指数的西南地区季节性干旱时空分布特征
Temporal and spatial distribution of seasonal drought in southwest of China based on relative moisture index
近60年来西南地区旱涝变化及极端和持续性特征认识
Extreme and persistent feature of drought and flood of Southwest China in past 60 years
近50a中国西南地区地表干湿状况研究
LStudy of surface dry and wet conditions in Southwest China in recent 50 years
基于SPEI的中国西南地区1961-2012年干旱变化特征分析
Characteristics of drought variations in Southwest China in 1961-2012 based on SPEI
热带大气MJO活动异常对2009-2010年云南极端干旱的影响
The influence of the Madden-Julian Oscillation activity anomalies on Yunnan’s extreme drought of 2009-2010
我国西南地区秋季干湿分类及主要类型异常年环流特征分析
Autumn dry-wet conditions and main types of atmospheric circulation in anomalous years in Southwest China
2006年夏季西南地区东部特大干旱及其大气环流异常
Features of the extremely severe drought in the east of Southwest China and anomalies of atmospheric circulation in summer 2006
基于SPEI的新疆干旱时空变化特征
SPEI-based spatiotemporal variation of drought in Xinjiang
Meteorological drought
The relationship of drought frequency and duration to time scales: Proceedings of Vulnerability
A multiscalar drought index sensitive to global warming: The standardized precipitation evapotranspiration index
中国自然地理(第4版)
Physical Geography of China(4th edition)
若尔盖气候变化及其对湿地退化的影响
Climate change in Zoigê Plateau marsh wetland and its impact on wetland degradation
我国西南地区干旱变化及对贵州水稻产量影响
Drought change in Southwest China and its impact on rice yield in Guizhou province
High resolution stalagmite δ18O record over the past 1000 year from Dongge Cave in Guizhou
Modern stalagmite oxygen isotopic composition and its implications of climatic change from a high-elevation cave in the eastern Qinghai-Tibet Plateau over the past 50 years
2010年春季西南地区干旱遥感监测及其影响评估
Drought monitoring and its impacts assessment in Southwest China using remote sensing in the spring of 2010
我国西南干旱研究最新进展综述
Summary of advance on drought study in Southwest China
近50年西南地区极端干旱气候变化特征
Climate characteristics of the extreme drought events in Southwest China during recent 50 years