中西亚极端干旱特征及其与热带海温的联系

干旱是影响中亚和西亚的首要自然灾害,作为“一带一路”倡议的枢纽地区,开展中西亚的干旱研究对“一带一路”倡议的顺利实施具有重要价值。本文利用自矫正帕尔默干旱指数（Self-calibrating Palmer Drought Severity Index,scPDSI）和ERA5再分析资料,分析了中西亚干旱发生发展的主要特征。结果表明中西亚干旱发展有明显的季节特征,干旱多是从前冬开始,春季迅速加强,春末达到最强,夏季开始逐渐缓解。利用合成分析方法,本文探讨了中西亚极端干旱和湿润事件的气候系统差异,结果表明：极端干旱事件前期热带太平洋海温呈现出La Ni?a海温异常模态,在西南亚激发出反气旋环流,导致中西亚南部低层持续的偏北风异常,使得来自印度洋的水汽输送减少,同时在中西亚对流层中层表现为EU2型遥相关特征,导致该地区出现正的高度场异常并不断加强。高度场正异常控制下大气以下沉运动为主,加之水汽输送减少,均不利于中西亚降水的产生,从而导致了中西亚干旱的迅速发展。     

中亚复合高温干旱事件识别与特征分析

由于复合高温干旱事件造成的综合效应远超普通干旱事件,复合高温干旱日益受到人们关注。基于中亚地区1981—2020年欧洲中期天气预报中心的第五代再分析陆地产品（Land Component of the Fifth Generation of European Reanalysis, ERA5-Land）的逐小时温度数据、月尺度潜在蒸散量数据和日尺度多源集成降水产品,计算标准化降水蒸散指数（Standardized Precipitation Evapotranspiration Index, SPEI）和日最高温度,识别复合高温干旱事件并分析其特征,得到以下结论：（1）复合高温干旱事件在中亚各地区空间分布上呈非集中趋势,1980年代、1990年代、2000年代和2010年代发生频次较高的区域分别位于东南部、北部、西北部和西部;（2）这些事件的时间分布表现出由大波动变为平稳小波动的趋势,且2020年之后将维持此平稳状态;（3）分析1984、1993、2010、2020年4个复合高温干旱事件典型年份,发现1984年高温干旱主要集中在中亚东南部,1993年仅零星地区偶发,2010年北部多发复...     

云南夏秋连续干旱事件及前期海平面气压异常信号

近十多年来云南地区多次发生极端的季节性连续干旱，尤其是夏季、秋季的连续干旱会加重传统冬、春季节干旱的危害，给当地经济和社会活动造成了严重的影响。本文基于1970～2019年云南省气象局120站降水数据及NCEP海平面气压场数据，从降水持续性异常指数出发，分析了云南夏、秋季节连续干旱事件发生的演变特征，进而探究了该区域夏秋连续干旱事件与前期4月海平面气压的可能联系，以期能够在极端干旱的预报中提供帮助。研究结果表明：（1）云南夏秋降水持续性异常的主要特征为全省一致的偏多或偏少；（2）云南夏秋连续干旱事件发生前期表现为3个区域海平面气压异常的组合，分别为北大西洋、北印度洋和中太平洋海平面气压异常；（3）由前期4月上述关键信号构建的组合信号指数，能够较好地表征云南夏季、秋季的降水连续异常，是具有意义的潜在前期预报信号。     

CMIP5全球气候模式对中国地区干旱变化模拟能力评估

利用东亚地区1961～2005年高分辨率（0．5°×0．5°）降水格点数据和参加CMIP5的42个全球气候模式数值模拟结果,通过对简单降水强度指数（降水距平百分率）的计算,对比分析了观测和多模式集合的中国地区干旱面积、干旱频率的时空分布以及干旱分布型的变化,评估了全球气候模式的模拟能力。结果表明：多个全球气候模式的集合结果对中国区域的干旱变化特征有一定的模拟能力,能较好地模拟出中国年平均干旱指数的时间变化趋势,但模拟的干旱强度偏弱;多模式集合模拟的严重干旱面积与观测值的变化趋势基本一致,与观测相比,模拟的长江以南干旱强度偏强,西北干旱强度偏弱;通过EOF的分析表明,多模式集合可以较好地模拟出西北与长江以南呈反位相及我国东部地区的“旱-涝-旱”或“涝-旱-涝”的分布型。     

升温1.5℃和2.0℃情景下中亚地区干旱耕地暴露度研究

基于CMIP5中的5个全球气候模式统计降尺度的降水、最高和最低气温等数据,利用标准降水蒸发指数（SPEI）和强度-面积-持续时间（IAD）方法识别全球升温1.5℃与2.0℃情景下中亚地区干旱事件,结合30 m分辨率土地利用数据,探讨中亚干旱事件的演变及耕地暴露度变化。结果表明：相比基准期（1986—2005年),中亚地区的降水和潜在蒸发量均有所增加;全球升温1.5℃与2.0℃情景下,中亚地区的干旱事件频次、强度和面积均将增加,其中重旱和极旱事件的频次和影响面积大幅上升,而中旱事件的频次和影响面积持续下降;1986—2005年中亚地区年均干旱耕地暴露度约11.5万km2,全球升温1.5℃和2.0℃情景下,干旱耕地暴露度将分别上升到17.9万km2和28.6万km2,且暴露在极旱下的耕地面积增加最明显。全球升温1.5℃与2.0℃情景下,增加的干旱事件将会严重威胁当地农业生产和粮食安全,中亚地区需对干旱事件采取长期的减缓与适应措施。     

中南半岛春季植被覆盖变化及其与ENSO的联系

利用归一化植被指数NDVI（Normalized Difference Vegetation Index）、气候资料以及环流场数据,探讨了中南半岛地区植被覆盖变化特征及其与ENSO（El Niño-Southern Oscillation）的联系。研究表明,降水是影响春季植被生长的主要因子,与NDVI呈显著的正相关关系;而温度、辐射与NDVI呈负相关关系。进一步分析表明,当前期冬季赤道中东太平洋海温异常偏暖（发生厄尔尼诺事件）时,中南半岛附近海平面气压偏高、850 hPa风场辐散,上升运动偏弱,不利于云和降水形成,而有利于太阳辐射增加和温度升高,降水减小和温度升高均抑制春季中南半岛植被生长;反之,当前期冬季发生拉尼娜事件时,有利于中南半岛植被生长。     

2017年春夏呼伦贝尔草原干旱过程多种监测指数对比分析

以2017年春夏季呼伦贝尔草原干旱过程为研究对象,利用呼伦贝尔草原范围内6个气象站的气温、降水数据和MODIS NDVI数据,分析对比2017年4—9月多种气象干旱指数（Pa30、SPI30、SPEI30、CI、MCI）与植被状态指数（VCI）的监测情况。结果表明：只考虑单一降水的气象干旱指数（Pa30、SPI30）在4月波动较大,且此类指数无法反映出高温等其他气象条件对干旱发展的影响。综合气象干旱指数(CI、MCI)由于引入多时间尺度干旱进行计算,旱情缓解时轻旱等级持续的时间过长,且草原植被在降水增加后的恢复速度较快,造成干旱缓解期间植被与监测结果差异较大。MCI与同期和前1期VCI的相关性最好,CI和SPEI30与前1期和前2期VCI的相关性较好,而只考虑单一降水的气象干旱指数与VCI的相关性普遍偏差。植被对SPEI30的响应时间更长,更适宜草原生态干旱的早期预警使用。     

基于大气-土壤-植被系统干旱发生发展过程的综合干旱指标构建与应用

适宜的干旱指标和高分辨率数据是准确监测干旱的基础.本研究从气象干旱和土壤干旱以及植被对干旱的响应出发,整合中国国家气象观测站、中国气象局陆面数据同化系统(CLDAS)土壤湿度(0.0625°×0.0625°)和MODIS叶面积指数(500?m×500?m)等多源数据信息,构建了基于气象干旱指数(标准化降水蒸散指数)、土...     

基于SPI的1961－2020年昌吉地区作物生长季气象干旱时空特征研究

基于昌吉地区7个气象站1961－2020年降水量资料，计算昌吉地区作物生长季标准化降水指数（SPI-7）。运用趋势分析法、M-K突变检验法和小波分析法探究了昌吉地区作物生长季SPI-7指数的年际和年代变化特征；在此基础上分析了作物生长季干旱的站次比和干旱强度的年际变化,并结合该区实际发生的旱灾对SPI进行了验证。结果表明：1961—2020年昌吉地区作物生长季标准化降水指数以0.08/10 a的速率呈微弱的正趋势（变湿），在年代变化趋势中呈现出变干-变湿-变干的变化波动, 1981年标准化降水指数由低到高突变；干旱强度呈增加趋势，干旱发生的区域面积有轻微减少的趋势；干旱强度在全区范围内主要为轻旱和中旱等级，并表现为全域性干旱和区域性干旱；空间分布上看干旱率最高区域在东部地区，轻旱主要集中在东部，中旱、重旱和特旱集中在西部地区，干旱强度大的区域大致分布在西部地区；在周期性变化方面，SPI指数存在着6年、9年、16年周期震荡；历史旱灾与SPI指数干旱评价结果吻合率较高，SPI指数在昌吉地区作物生长季的干旱监测与分析中具有较好的实用性。     

基于温度植被干旱指数（TVDI）的甘肃省农业干旱监测方法研究

改进温度植被干旱指数（Temperature Vegetation Dryness Index,TVDI）并明确TVDI的农业干旱等级阈值,对提高TVDI指数监测农业干旱能力有重要意义。利用近19 a的MODIS(Moderate Resolution Imaging Spectro-radiometer,MODIS)遥感数据,基于单时次和多时次方法构建NDVI(Normalized Difference Vegetation Index,NDVI)-LST(Land Surface Temperature,LST)、EVI(Enhanced Vegetation Index,EVI)-LST、RVI(Ratio Vegetation Index,RVI)-LST、SAVI(Soil-Adjusted Vegetation Index,SAVI)-LST等几种特征空间,讨论TVDI计算方法,分析TVDI在甘肃省农业干旱监测中的适用性,并明确甘肃省夏季TVDI农业干旱分级标准。结果表明：（1）基于多时次方法构建的SAVI-LST特征空间TVDI更适合甘肃省农业干旱监测,其对土壤相对湿度（...     

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1986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（1961～2000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21个站的有关资料（1961～2000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0～20 cm和20～100 cm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139个站点（1961年1月～2000年12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，适合应用于我国     

On the potential application of land surface models for drought monitoring in China

The potential of using land surface models (LSMs) to monitor near-real-time drought has not been fully assessed in China yet. In this study, we analyze the performance of such a system with a land surface model (LSM) named the Australian Community Atmosphere Biosphere Land Exchange model (CABLE). The meteorological forcing datasets based on reanalysis products and corrected by observational data have been extended to near-real time for semi-operational trial. CABLE-simulated soil moisture (SM) anomalies are used to characterize drought spatial and temporal evolutions. One outstanding feature in our analysis is that with the same meteorological data, we have calculated a range of drought indices including Standardized Precipitation Index (SPI), Standardized Precipitation-Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI). We have assessed the similarity among these indices against observed SM over a number of regions in China. While precipitation is the dominant factor in the drought development, relationships between precipitation, evaporation, and soil moisture anomalies vary significantly under different climate regimes, resulting in different characteristics of droughts in China. The LSM-based trial system is further evaluated for the 1997/1998 drought in northern China and 2009/2010 drought in southwestern China. The system can capture the severities and temporal and spatial evolutions of these drought events well. The advantage of using a LSM-based drought monitoring system is further demonstrated by its potential to monitor other consequences of drought impacts in a more physically consistent manner.     

Use of the National Drought Model (NDM) in Monitoring Selected Agroclimatic Risks Across the Agricultural Landscape of Canada

Abstract

The National Drought Model (NDM) is an amalgamation of the atmospheric component of the original Palmer Drought and Versatile Soil Moisture Budget (VSMB) models. The NDM uses locally derived coefficients from the station or gridded climate data to calculate a calibration factor for comparing locations in time and space. A modular approach is used to model major processes such as evapotranspiration, biometeorological time, snowmelt, and the cascading of soil moisture down to the root zone. The modular approach allows modifications to be made to specific sections without making structural changes to the entire model or the data inputs. The NDM is an operational tool, integrating data from the climate, soil, and plant sciences to monitor agroclimatic risks such as drought and excess moisture. In this paper, the capacity of the NDM to monitor extreme agroclimatic risks, such as drought and flooding of agricultural soils, was assessed. Using the Palmer Drought Severity Index component of the NDM, the mapping of the spatial extent and severity of the 2001 and 2002 droughts across Canada and the excess moisture conditions on the Canadian Prairies in 2010 agreed with other assessments. The validation study of soil moisture at two Alberta locations (Lethbridge and Beaverlodge) showed that the VSMB tracked the soil moisture flux in the root zone successfully in response to changing environmental conditions. The VSMB explained about 70 and 60% of the variance in observed soil moisture at the two respective locations.     

Frequency and duration of historical droughts from the 16th to the 19th centuries in the Mexican Maya lands, Yucatan Peninsula

Using unprecedented catalogues of past severe drought data for the Yucatan Peninsula between 1502 and 1900 coming from historical written documentation, we identified five conspicuous time lapses with no droughts between 1577–1647, 1662–1724, 1728–1764, 1774–1799 and 1855–1880, as well as time epochs with most frequent droughts between 1800 and 1850. Moreover, the most prominent periodicity of the historical drought time series was that of ∼40 years. Using the Palmer Drought Severity Index for the Yucatan Peninsula for the period 1921–1987 we found prominent negative phases between ∼1942–1946 and 1949–1952, 1923–1924, 1928–1929, 1935–1936, 1962–1963, 1971–1972 and 1986–1987. Two prominent periodicities clearly appear at ∼5 and 10 years. Most modern and historical severe droughts lasted 1 year, and share a quasi-decadal frequency. Also, in the first 66 years of the twentieth century the frequency of occurrence of severe drought has been lower compared with the nineteenth century. Some of the major effects and impacts of the most severe droughts in the Yucatan region are examined. We also studied the relation between historical and modern droughts and several large scale climate phenomena represented by the Atlantic Multidecadal Oscillation (AMO) and the Southern Oscillation Index (SOI). Our results indicate that historical droughts and the cold phase of the AMO coincide, while the influence of the SOI is less clear. The strongest coherence between historical droughts and AMO occurred at periodicities of ∼40 years. For modern droughts the coherence of a drought indicator (the Palmer Drought Severity Index) is similar with AMO and SOI, although it seems more sustained with the AMO. They are strongest at ∼10 years and very clearly with the AMO cold phase. Concerning the solar activity proxies and historical droughts, the coherence with a record of beryllium isotope Be¹⁰, which is a good proxy of cosmic rays, is higher than with Total Solar Irradiance. We notice that the strongest coherence between historical droughts and Be¹⁰ occurs at periods ∼60–64 years. When studying modern droughts and solar activity, frequencies of ∼8 years appear, and the coherences are similar for both sunspots and cosmic rays. Comparing natural terrestrial and solar phenomena, we found that the most sustained and strongest modulation of historical drought occurrence is at ∼60–64 years and is between the historical drought series and the solar proxy Be¹⁰. For modern droughts we notice that the coherence is similar among AMO, SOI and the solar indices. We can conclude that the sea surface temperatures (AMO) and solar activity leave their signal in terms of severe droughts in the Maya lands, however in the long term, the influence of the SOI on this type of phenomenon is less clear.     

近20年华北地区干旱期大气环流异常特征

利用NCAR/NCEP再分析资料和中国气象局整编的中国160站气温、降水月平均资料, 计算并分析了1951年1月-2000年10月中国华北地区Palmer drought severity index (PDSI)。研究表明:近50年来华北干旱有显著的年际和年代际变化。从20世纪80年代以来, 华北出现了持续性严重干旱现象; 另外, 华北地区干旱持续时间一般都在两年以上。华北夏季典型干旱年的前期 (冬季和春季) 及同期环流特征是:北半球中高纬度500hPa高度距平场出现EU型遥相关分布, 华北地区长期处于大陆暖高压控制下。     

Investigation of seasonal droughts and related large-scale atmospheric dynamics over the Potwar Plateau of Pakistan

As a result of climate change and unsustainable land use management in the recent past, droughts have become one of the most devastating climatic hazards whose impacts may prolong from months to years. This study presents analysis of droughts for two major cropping seasons, i.e., Kharif (May–September) and Rabi (October–April), over the Potwar Plateau of Pakistan. The analysis is performed using various datasets viz. observational, reanalysis, and Regional Climate Models (RCMs), for the past (1981–2010) and future (2011–2100) time periods. The following two methods for the identification of dry and wet years, also referred to as drought and wetness, are applied: (1) the percentile rank approach and (2) the drought indices, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI). Future projections of droughts are investigated using RCM (RegCM4.4 and RCA4) outputs from CORDEX South Asia domain under two Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5. Generally, the indices show non-significant decreasing trends of drought severity in the recent past for all cases; however, significant increasing trends are observed for annual (0.006) and Kharif (0.007) cases under RCP4.5 scenario. The analysis of large-scale atmospheric dynamics suggests the significant role of low-level geopotential height anomalies over Tibetan Plateau (northwest of Pakistan) during Kharif (Rabi) season in controlling drought occurrence by transporting moisture from the Bay of Bengal (Arabian Sea). Moreover, composites of vertically integrated moisture transport, moisture flux convergence/divergence, and precipitable water anomalies show their marked contribution in maintaining the drought/wetness conditions over the Potwar region.     

Severity, duration and frequency of drought in SE England from 1697 to 2011

Severe droughts have affected much of Europe over the last 40 years. A limitation to current understanding of droughts is based around drought characteristics (e.g. frequency, severity and duration) as there are limited long series (>100 years) with well documented severe droughts. This is further complicated with future climate projections, and the potential implications that these will have on drought characteristics. This paper presents reconstructed drought series from 1697, 1726 and 1767 to 2011 for three sites in southeast England. Precipitation and temperature series are reconstructed to generate long drought series using the self-calibrated Palmer Drought Severity Index, enabling determination of drought characteristics. The reconstructions identify multiple drought-rich periods, 1730–1760 and 1890-present, with an increasing tendency towards more severe droughts during the latter period. Prolonged rainfall deficiencies are found to be the primary cause of severe droughts, with rising temperatures increasing soil moisture deficit, therefore intensifying drought conditions. Cycles at the 6–10 year period identify a sub-decadal to decadal signal during drought-rich periods. Analysis of the spatial variability of droughts finds that whilst severe events are predominantly regionally coherent, there are notable variations in severity and duration between sites, which are attributed to localised rainfall variability. This study extends the temporal range of previous drought studies and places recent drought events in a longer context improving upon existing ‘benchmark’ drought analyses in southeast England; with far-reaching implications for local, national and continental scale reduction of drought vulnerability and risk.     

Characteristics of Clustering Extreme Drought Events in China During 1961-2010

Based on the Multi-Scale Standardized Precipitation Index (MSPI), extreme severe drought events in China during 1961-2010 were identified, and the seasonal, annual, and interdecadal variations of the clustering extreme drought events were investigated by using the spatial point process theory. It is found that severe droughts present a trend of gradual increase as a result of the significant increase and clustering tendency of severe droughts in autumn. The periodicity analysis of the clustering extreme droughts in different seasons suggests that there is a remarkable interdecadal change in the occurrence of clustering extreme droughts in winter. Meanwhile, it is revealed that the clustering extreme drought events exhibit greatly different annual mean spatial distributions during 1961-2010, with scattered and concentrated clustering zones alternating on the decadal timescale. Furthermore, it is found that the decadal-mean spatial distributions of extreme drought events in summer are correlated out of phase with those of the rainy bands over China in the past 50 years, and a good decadal persistence exists between the autumn and winter extreme droughts, implying a salient feature of consecutive autumn-winter droughts in this 50-yr period. Compared with other regions of China, Southwest China bears the most prominent characteristic of clustering extreme droughts.     

干旱严重指数（DSI）在内蒙古地区的适用性分析

利用MODIS遥感产品计算内蒙古地区2000—2019年植被生长季的干旱严重指数(DSI),并结合气象干旱综合指数(MCI)、植被状态指数(VCI)等干旱指数和典型干旱过程,对DSI在内蒙古地区的适用性进行分析。研究表明,DSI与MCI、VCI的平均相关系数为0.509和0.839,分别通过0.05和0.01的显著性检验,具有较好的一致性。与MCI相比,DSI具有更高的空间分辨率,能反映不同植被类型抗旱能力的差异和区域植被改善后抗旱能力的增强。与VCI相比,DSI受高植被覆盖区归一化植被指数(NDVI)饱和现象的影响更小,并在干旱缓解期的灵敏性更高。DSI在内蒙古地区的适用性较好,可在干旱监测研究与业务中进行尝试和使用。