Projected Changes of Palmer Drought Severity Index under an RCP8.5 Scenario

The potential change of drought measured by the Palmer Drought Severity Index （PDSI） is projected by using a coupled climate system model under a Representative Pathway 8.5 （RCP8.5） scenario.The PDSI changes calculated by two potential evapotranspiration algorithms are compared.The algorithm of Thomthwaite equation overestimates the impact of surface temperature on evaporation and leads to an unrealistic increasing of drought frequency.The PM algorithm based on the Penman-Monteith equation is physically reasonably and necessary for climate change projections.The Flexible Global Ocean-Atmosphere-Land System model,Spectral Version 2 （FGOALS-s2） projects an increasing trend of drought during 2051-2100 in tropical and subtropical areas of North and South America,North Africa,South Europe,Southeast Asia,and the Australian continent.Both the moderate drought （PDSI ＜-2） and extreme drought （PDSI ＜-4） areas show statistically significant increasing trends under an RCP8.5 scenario.The uncertainty in the model projection is also discussed.

Evaluation of Spatial-Temporal Variability of Drought Events in Iran Using Palmer Drought Severity Index and Its Principal Factors (through 1951-2005)

Intensity and variability of droughts are considered inIranduring the period 1951 to 2005. Four variables are considered: the Palmer Drought Severity Index (PDSI), the soil moisture, the temperature and the precipitation (products used for the analysis are downloaded from the NCAR website). Link with the climatic indexLa Ninais also considered (NOAA downloadable products is used). The analysis is based on basic statistical approaches (correlation, linear regressions and Principal Component Analysis). The analysis shows that PDSI is highly correlated to the soil moisture and poorly correlated to the other variables—although the temperature in the warm season shows high correlation to the PDSI and that a severe drought was experienced during 1999-2002 inthe country.

Temporal and spatial variations in the Palmer Drought Severity Index over the past four centuries in arid, semiarid,and semihumid East Asia

Based on a database of 106 annually resolved tree-ring chronologies and 244 Palmer Drought Severity Index(PDSI)grid data,we attempted to reconstruct gridded spatial drought patterns in each year over the past four centuries in the arid,semiarid,and semihumid East Asia.The results showed that these regions mainly experienced drought events during the periods from AD 1601 to AD 1652,AD 1680 to AD 1718,AD 1779 to AD 1791,AD 1807 to AD 1824,AD 1846 to AD 1885,and AD 1961 to AD 1999.In the middle of the 16th century,severe droughts occurred mainly in North China;during the period from AD 1876 to AD 1878,droughts occurred in most parts of northern China;and from the 1920s to 1940s,catastrophic drought events spread across almost all of northern China and Mongolia.These historical drought events caused severe ecological and environmental problems and substantially affected the development of human society.In these regions,temperature and summer monsoon precipitation are the main factors influencing drought events.In western areas,PDSI and temperature exhibit a close relationship,whereas in eastern areas,summer monsoon rainfall is the dominant factor influencing variations in PDSI.

Palmer干旱指数在华北干旱分析中的应用

利用中国气象局整编的1951年1月～2000年10月中国160站气温、降水月平均资料,计算了1951年1月～2000年10月我国160站修正的Palmer drought severity index(PDSI).PDSI指数对我国的干旱和洪涝过程都有很好的指示意义.华北地区干旱持续性非常强,持续时间一般都在两年以上.华北地区干旱不但年际变化大,年代际变化也显著,近50年来华北干旱主要发生在20世纪70年代以后,且干旱强度有所增加.夏季伴随干旱过程常常出现高温酷暑天气.

径流量Z指数与Palmer指数对河西干旱的监测

利用河西内陆河水文代表站1959—2004年逐月径流量资料、内陆河流域灌溉区1949—2001年耕地面积及代表站1961—2005年的气象资料,通过对径流量进行正态化处理来确定径流量Z指数,并以径流量Z指数作为径流干旱指数,对旱涝等级进行划分;考虑径流量Z指数的旱涝等级与农业灌溉用水实际情况之间的关系,给出了径流量Z指数的灌溉指标。将径流量转化为降水量,改进Palmer旱度模式,且在作改进后,又将潜在蒸散量的计算法由利用桑斯威特公式改为利用彭曼公式。结果表明:将径流量考虑到Palmer干旱指数中并改变蒸散量的算法,使得该指数对河西灌溉区干旱情况的监测均有所改善。对照河西地区的干旱事件,径流量Z指数监测到的干旱情况,比Palmer干旱指数改进前、后监测到的干旱情况效果更佳。径流量Z指数能更真实地反映河西灌溉区干旱状况。

Palmer干旱指数、地表湿润指数与降水距平的比较

利用中国气象局整编的1951年1月～1999年12月中国160站气温、降水月平均资料,计算了我国160站近49年逐月帕尔默干旱指数、地表湿润指数和降水距平百分率。对比研究表明:PDSI指数和地表湿润指数能抓住降水是干旱最重要的决定因素这一特征,并且,能反映出干旱过程具有更大的时空尺度。在实际蒸发较大的地区,PDSI指数比降水距平百分率描述干旱强度更准确。对于华北地区,在20世纪80年代以前,降水偏多,气温偏低,最大潜在蒸发较小,处于相对湿润的时段;80年代以后,降水偏少,加之气温的升高,华北的干旱越来越严重。

基于改进失水模式和增加建模站点的Palmer旱度模式

根据1965年Palmer旱度模式的思路,在1986年修正版及2003年修正版的基础上,为了使Palmer旱度模式更适用于我国北方干旱、半干旱地区,通过改进2003年修正的Palmer旱度模式在建模时表层失水模式的假设以及增加建模站点个数两个方面对Palmer旱度模式进行进一步修正。将计算的Palmer指数值与2003年计算的Palmer指数值及一些文献记载的实际旱涝灾情相对照进行验证,结果表明:新修正的Palmer旱度模式能更好地评估旱涝情况,扩大其在我国干旱地区的适用性。

基于Palmer指数的朝阳地区1952-2015年干旱演变特征研究

利用辽宁省朝阳市6个地区的气象站1952-2015年期间64年的逐日降水量、气温等气象数据计算其Palmer干旱指数,并应用小波分解对PDSI指数进行多分辨率分析,从而探究了该地区干旱发生等级、频次、覆盖范围、周期、突变等时间演变特性及发生规律,将为农业生产、抗灾预警、救灾措施制定等工作提供理论依据。研究结果表明,朝阳地区年干旱变化呈明显的5年小周期和10年大周期重复,夏季和秋季发生多次干旱突变,1980s突变较为明显;秋季的干旱情况最为严重、夏季的干旱次之、冬季和春季的干旱程度较轻;年、春、夏、秋、冬干旱发生频次分别为5.72、1.3、1.59、1.56、1.41个月;干旱覆盖范围分别为82.6%、38.0%、48.2%、47.9%和37.0%。

基于scPDSI的东北地区气象干旱时空特征分析

干旱已成为全球陆地生态系统面临的普遍问题,其发展具有明显的地域特征,了解区域干旱的时空分布特征是防灾减灾、应对气候变化的基础。基于scPDSI数据集,采用经验正交函数和统计分析方法,分析2002-2017年东北地区气候干湿状况的时空分布和演变特征,探讨了干湿状况的季节变化对年际变化的贡献率,结果表明:东北地区4个季节的干旱面积为52.27%-62.03%,虽然季节和年际尺度的干旱均有减弱趋势,其中冬季干旱程度显著减弱,但干旱仍然是东北地区的主要气候背景;春季和夏季scPDSI的协同作用对年际scPDSI变化的贡献率达88.64%,夏季的贡献率达86.13%;东北地区的西部干旱程度高于东部的,其中呼伦贝尔草原中部和浑善达克沙地东部以严重干旱和中等干旱为主;EOF分析表明,东北地区4个季节和年度的干湿状况呈现一致的正变化趋势,高值中心主要出现在南部地区。

Analysis of spatio-temporal evolution of droughts in Luanhe River Basin using different drought indices

Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index （SPEI） and standardized precipitation index （SPI） at three- and six-month time scales and the self-calibrating Palmer drought severity index （sc-PDSI） were calculated to evaluate droughts in the study area. Temporal variations of the drought severity from 1960 to 1989 were analyzed and compared based on the results of different drought indices, and some typical drought events were identified. Spatial distributions of the drought severity according to the indices were also plotted and investigated. The results reveal the following： the performances of different drought indices are closely associated with the drought duration and the dominant factors of droughts; the SPEI is more accurate than the SPI when both evaporation and precipitation play important roles in drought events; the drought severity shown by the sc-PDSI is generally milder than the actual drought severity from 1960 to 1989; and the evolution of the droughts is usually delayed according to the scPDSI. This study provides valuable references for building drought early warning and mitigation systems in the Luanhe River Basin.

Performance of different drought indices for agriculture drought in the North China Plain

The Palmer drought severity index （PDSI）, standardized precipitation index （SPI）, and standardized precipitation evapotranspiration index （SPEI） are used worldwide for drought assessment and monitoring. However, substantial differences exist in the performance for agricultural drought among these indices and among regions. Here, we performed statistical assessments to compare the strengths of different drought indices for agricultural drought in the North China Plain. Small differences were detected in the comparative performances of SPI and SPEI that were smaller at the long-term scale than those at the short-term scale. The correlation between SPI/SPEI and PDSI considerably increased from 1- to 12-month lags, and a slight decreasing trend was exhibited during 12- and 24-month lags, indicating a 12-month scale in the PDSI, whereas the SPI was strongly correlated with the SPEI at 1- to 24-month lags. Interestingly, the correlation between the trend of temperature and the mean absolute error and its correlation coefficient both suggested stronger relationships between SPI and the SPEI in areas of rapid climate warming. In addition, the yield-drought correlations tended to be higher for the SPI and SPEI than that for the PDSI at the station scale, whereas small differences were detected between the SPI and SPEI in the performance on agricultural systems. However, large differences in the influence of drought conditions on the yields of winter wheat and summer maize were evident among various indices during the crop-growing season. Our findings suggested that multi-indices in drought monitoring are needed in order to acquire robust conclusions.

Meteorological drought in semi-arid regions:A case study of Iran

Drought occurs in almost all climate zones and is characterized by prolonged water deficiency due to unbalanced demand and supply of water,persistent insufficient precipitation,lack of moisture,and high evapotranspiration.Drought caused by insufficient precipitation is a temporary and recurring meteorological event.Precipitation in semi-arid regions is different from that in other regions,ranging from 50 to 750 mm.In general,the semi-arid regions in the west and north of Iran received more precipitation than those in the east and south.The Terrestrial Climate(TerraClimate)data,including monthly precipitation,minimum temperature,maximum temperature,potential evapotranspiration,and the Palmer Drought Severity Index(PDSI)developed by the University of Idaho,were used in this study.The PDSI data was directly obtained from the Google Earth Engine platform.The Standardized Precipitation Index(SPI)and the Standardized Precipitation Evapotranspiration Index(SPEI)on two different scales were calculated in time series and also both SPI and SPEI were shown in spatial distribution maps.The result showed that normal conditions were a common occurrence in the semi-arid regions of Iran over the majority of years from 2000 to 2020,according to a spatiotemporal study of the SPI at 3-month and 12-month time scales as well as the SPEI at 3-month and 12-month time scales.Moreover,the PDSI detected extreme dry years during 2000-2003 and in 2007,2014,and 2018.In many semi-arid regions of Iran,the SPI at 3-month time scale is higher than the SPEI at 3-month time scale in 2000,2008,2014,2015,and 2018.In general,this study concluded that the semi-arid regions underwent normal weather conditions from 2000 to 2020.In a way,moderate,severe,and extreme dry occurred with a lesser percentage,gradually decreasing.According to the PDSI,during 2000-2003 and 2007-2014,extreme dry struck practically all hot semi-arid regions of Iran.Several parts of the cold semi-arid regions,on the other hand,only experienced moderate to severe dry from 2000 to 2003,except for the eastern areas and wetter regions.The significance of this study is the determination of the spatiotemporal distribution of meteorological drought in semi-arid regions of Iran using strongly validated data from TerraClimate.

Drought fluctuations based on dendrochronology since 1786 for the Lenglongling Mountains at the northwestern fringe of the East Asian summer monsoon region

The Lenglongling Mountains （LLM） located in northeastern part of the Tibet Plateau, belong to a marginal area of the East Asian summer monsoon （EASM） and are sensitive to monsoon dynamics. Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability. Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index （sc_PDSI） were significant and stable across time, demonstrating the strength of sc_PDSI in modeling drought conditions in this region. Based on the relationships, the mean sc_PDSI was reconstructed for the period from 1786 to 2013. Dry conditions prevailed during 1817-1819, 1829-1831, 1928-1931 and 1999-2001. Relatively wet periods were identified for 1792-1795 and 1954-1956. Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China, long-term variability of moisture conditions was synchronous before the 1950s at a decadal scale （1791-1954）. In northwestern margin of the EASM, most of all selected reconstructions had better consistency in low-frequency variation, especially during dry periods, indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region.

帕默尔干旱指标及其应用研究进展

干旱灾害是世界各国,尤其是我国最为严重的自然灾害之一。不同领域、不同应用中所定义的干旱指标各不相同。气象干旱是其他各类干旱的基础,而帕默尔(Palmer)干旱指标是气象干旱的主流指标,有着广泛的影响,该指标能反映干旱的成因、程度及开始、结束和持续时间,具有物理意义明确、涉及资料容易获得和参数计算简便等特点。根据国内外大量文献,对帕默尔干旱指标的研究进展进行了回顾,对其应用进行了总结,同时对未来帕默尔旱度模式的进一步修正进行了展望。

新疆气候的干湿变化及其趋势预估

利用新疆气象局提供的90个气象台站的连续观测记录,计算了1961-2003年新疆地区年平均和季节平均自适应Palmer干旱指数的气候态及其变化趋势,表明新疆地区气候就平均态而言整体上属于正常的气候条件,研究时段内年平均和季节平均气候以湿润化趋势为主要变化特征,定性的分析显示地表气温的持续上升倾向于引起干旱化,而降水的增加则有利于气候的湿润化趋势。在SRES A2温室气体和气溶胶排放情景下,21世纪90年代新疆地区地表气温的升高会导致干旱化的发生,而降水的增加则有利于湿润化,在二者的联合作用下,新疆地区的干湿状况可能将发生一定程度的变化。

帕默尔旱度模式的进一步修正

为了正确评估干旱 ,根据帕默尔旱度模式的思路和 1 986年安顺清等人修正的帕默尔旱度模式 ,我们以济南、郑州和太原 3站逐年逐月气温和降水等作为基本资料 ( 1 961～ 2 0 0 0年 ) ,以哈尔滨、佳木斯、呼和浩特、沈阳、北京、固原、西安、汉中、青岛、德州、运城、长沙、武汉、南昌、杭州、福州、广州、昆明、南宁、成都和贵阳 2 1个站的有关资料 ( 1 961～ 2 0 0 0年 )为权重因子修正资料 ,并且在计算可能蒸散时选用了FAO推荐的彭曼 蒙蒂斯公式。另外 0～2 0cm和 2 0～ 1 0 0cm土层的土壤田间有效持水量根据我国测定的资料和土壤特性确定 ,对帕默尔旱度模式进行了进一步修正。利用此模式计算了我国北方地区 1 39个站点 ( 1 961年1月～ 2 0 0 0年 1 2月 )的帕默尔指数值。将计算的帕默尔指数值与一些文献记载的实际旱涝灾情相对照进行验证 ,表明进一步修正的帕默尔旱度模式能较为准确地评估旱涝情况 。

基于PDSI和SPI的综合气象干旱指数研究

在总结对比已有气象干旱指数的基础上,结合帕默尔干旱指数(PDSI)和标准化降水指数(SPI)的优点,提出综合气象干旱指数DI,并对综合气象干旱指数与区域干旱受旱/成灾面积和径流丰枯的相互关系进行分析,结果表明:综合气象干旱指数能够较好地反映区域干旱受旱/成灾范围,以及河道径流的丰枯状况。并且综合气象干旱指数还同时考虑了月季降水量的异常和一段时间的水分亏缺,比单个气象干旱指数更能反映农业干旱和水文干旱。

黄河流域极端干旱的时空演变特征及多变量统计模型研究

干旱是黄河流域经常性发生的自然灾害之一,给该地区的社会生产、人民生活带来了巨大的影响.本文选取黄河流域61个气象站点1960—2009年的气象资料,计算每个站点月尺度和年尺度的PDSI指数,分析了该地区极端干旱和干旱的时空演变特征,并利用Copula函数,构建干旱历时和干旱强度之间的两变量统计模型,研究该地区干旱发生风险的空间分异特征.研究发现,黄河流域在过去50年有逐渐变旱的趋势,其中20世纪60年代该地区降水较为丰沛,但也有少部分年份发生了比较严重的干旱.20世纪80年代以后,黄河流域极端干旱和干旱的发生频次均有增加的趋势.黄河流域干旱发生频率大体上呈现出北高东南低的空间分布特征.通过对特定站点(陕西吴旗站)的分析,发现干旱历时和干旱强度之间具有很好的相依性,从Chi图中可以反映出上述两个变量之间具有上尾相关的特征.K-S检验的结果表明,指数分布和Gamma分布能够分别很好的拟合干旱历时和干旱强度.拟合优度检验的结果表明,在所选择的3种Copula函数中,Gumbel Copula能够较好的描述干旱历时和干旱强度之间的相关结构.重现期分析的结果表明,黄河上游和中游北部发生干旱的风险相对较高,而流域下游地区风险相对较低.

帕尔默旱度指数方法在全国实时旱情监视中的应用

在进一步修正的帕尔默旱度指数月模式的基础上研制了帕尔默旱度指数日模型,同时采用了权重帕尔默旱度指数方法实现了逐日帕尔默旱度指数计算。经过对全国556个气象测站的参数调试,建立了全国范围帕尔默旱度指数实时业务应用系统,一年多的运行表明,帕尔默旱度指数确实能够较好地及时反映实时旱涝情况和变化过程。

基于帕尔默旱度模式的干旱识别及其特征值频率分析

干旱过程识别及干旱特征值频率分析是旱灾风险管理的重要基础性工作。目前干旱频率分析中存在的主要问题有:水文干旱指标易受人类活动影响,其序列的一致性条件常难满足;基于阈值的干旱过程识别法中存在着阈值无明确物理意义;干旱历时定义为干旱过程中的时段数,会使过程中有较多旱情缓解期但烈度并不大的干旱因干旱历时较长而被识别为严重干旱;干旱烈度常不具有时间可比性。采用受人类活动影响较小的气象因子为输入,基于帕尔默旱度模式计算了研究区逐时段的干、湿状态及帕尔默干旱指数,根据其干、湿状态及帕尔默干旱指数识别了干旱过程,以干旱过程中处于干期状态的时段数为干旱历时并以干旱过程中具有时间可比性的帕尔默水分距平指数的累积值为干旱烈度。在采用适线法确定干旱历时、干旱烈度分布的基础上,利用GH Copula函数构建了两者的联合分布,计算了昆明站1951-2011年干旱事件的重现期,其中2009-2010年干旱为61 a资料中最严重干旱,重现期达64.7 a一遇。经与昆明实际旱情及由降水、径流指标识别的干旱过程比较,表明基于帕尔默旱度模式识别的干旱过程能较好地反映实际旱情,与由径流指标识别的干旱过程具有较高一致性,而与未涉及地表水文过程的降水指标识别的干旱过程有所差异。研究结果为旱灾危险性评估提供参考。