Characteristics of Drought and Flood in Zhejiang Province,East China:Past and Future

On the basis of large amount of historical and measured data, this paper analyzed the regional, periodic, frequency, continuing, and response characteristics of droughts and floods in Zhejiang and proposed the conception of ratio of peak runoff. Main characteristics of droughts and floods in Zhejiang are as follows： 1） The western Zhejiang region is plum rain major control area, and the eastern coastal region of Zhejiang is typhoon major control area. 2） Within a long period in the future, Zhejiang will be in the long period that features droughts. 3） In Zhejiang the 17th century was frequent drought and flood period, the 16th, 19th, and 20th centuries were normal periods, while the 18th century was spasmodic drought and flood period. 4） The severe and medium floods in Zhejiang were all centered around the M-or m-year of the 11-year sunspot activity period. 5） There are biggish years of annual runoff occurred in E1 Nifio year （E） or the following year （E＋1） in Zhejiang. The near future evolution trend of droughts and floods in Zhejiang is as follows： 1） Within a relatively long period in the future, Zhejiang Province will be in the long period of mostly drought years. 2） Between 1999 and 2009 this area will feature drought years mainly, while the period of 2010-2020 will feature flood years mostly. 3） Zhejiang has a good response to the sunspot activities, and the years around 2009, 2015, and 2020 must be given due attention, especially around 2020 there might be an extremely severe flood year in Zhejiang. 4） Floods in Zhejiang have good response to El Nifio events, in El Nifio year or the following year much attention must be paid to. And 5） In the future, the first, second, and third severe typhoon years in Zhejiang will be 2009. 2012. and 2015. resnectivelv.

Extreme Weather and Climate Events and Their Impacts on Island Countries in the Western Pacific: Cyclones, Floods and Droughts

Increases in the frequency of extreme weather and climate events and the severity of their impacts on the natural environment and society have been observed across the globe in recent decades. In addition to natural climate variability and greenhouse-induced climate change, extreme weather and climate events produce the most pronounced impacts. In this paper, the climate of three island countries in the Western Pacific: Fiji, Samoa and Tuvalu, has been analysed. Warming trends in annual average maximum and minimum temperatures since the 1950s have been identified, in line with the global warming trend. We present recent examples of extreme weather and climate events and their impacts on the island countries in the Western Pacific: the 2011 drought in Tuvalu, the 2012 floods in Fiji and a tropical cyclone, Evan, which devastated Samoa and Fiji in December 2012. We also relate occurrences of the extreme weather and climate events to phases of the El Niño-Southern Oscillation (ENSO) phenomenon. The impacts of such natural disasters on the countries are severe and the costs of damage are astronomical. In some cases, climate extremes affect countries to such an extent that governments declare a national state of emergency, as occurred in Tuvalu in 2011 due to the severe drought’s impact on water resources. The projected increase in the frequency of weather and climate extremes is one of the expected consequences of the observed increase in anthropogenic greenhouse gas concentration and will likely have even stronger negative impacts on the natural environment and society in the future. This should be taken into consideration by authorities of Pacific Island Countries and aid donors when developing strategies to adapt to the increasing risk of climate extremes. Here we demonstrate that the modern science of seasonal climate prediction is well developed, with current dynamical climate models being able to provide skilful predictions of regional rainfall two-three months in advance. The dynamic climate model-based forecast products are now disseminated to the National Meteorological Services of 15 island countries in the Western Pacific through a range of web-based information tools. We conclude with confidence that seasonal climate prediction is an effective solution at the regional level to provide governments and local communities of island nations in the Western Pacific with valuable assistance for informed decision making for adaptation to climate variability and change.

Simulation of Extreme Climate Events over China with Different Regional Climate Models

During phase II of the Regional Climate Model Inter-comparison Project （RMIP） for Asia, the Asian climate was estimated from July 1988 to December 1998 using six climate models. In this paper, the abilities of six climate models to simulate several important ex- treme climate events in China during the last years of the last century were analyzed. The modeled results for the intensity of the precipitation anomaly over the Yang- tze-Huaihe Valley during the summers of 1991 and 1998 were weaker than the observed values. The positive pre- cipitation anomaly responsible for a catastrophic flood in 1991 was well reproduced in almost all simulation results, but the intensity and range of the precipitation anomaly in 1998 were weaker in the modeled results. The spatial dis- tribution of extreme climate events in 1997, when severe drought affected North China and flood impacted South China, was reproduced by most of the regional models because the anomaly of the large-scale background field was well-simulated, despite poor simulation of high temperature areas in the north during the summer by all models.

Large-scale atmospheric singularities and summer long-cycle droughts-floods abrupt alternation in the middle and lower reaches of the Yangtze River

The daily precipitation data at 720 sta- tions over China for the 1957―2003 period during summer (May―August) are used to investigate the summer subseasonal long-cycle droughts-floods abrupt alternation (LDFA) phenomenon and a long-cycle droughts-floods abrupt alternation index (LDFAI) in the middle and lower reaches of the Yangtze River (MLYRV) is defined to quantify this phenomenon. The large-scale atmospheric circula- tion features in the anomalous LDFA years are ex- amined statistically. Results demonstrate that the summer droughts-to-floods (DTF) in the MLYRV usually accompany with the more southward western Pacific subtropical high (WPSH), negative vorticity, strong divergence, descending movements develop- ing and the weak moisture transport in the low level, the more southward position of the South Asia high (SAH) and the westerly jets in the high level during May―June, but during July―August it is in the other way, northward shift of the WPSH, positive vorticity, strong convergence, ascending movements and strong moisture transport in the low level, and the northward shift of the SAH and the westerly jets in the high level. While for the summer floods-to-droughts (FTD) in the MLYRV it often goes with the active coldair mass from the high latitude, positive vorticity, strong convergence, ascending movement develop- ing and the strong moisture transport in the low level, and the SAH over the Tibetan Plateau in the high level, but during July―August it is often connected with the negative vorticity, strong divergence, de- scending movements developing and the weak moisture transport in the low level, the remarkable northward shift of the WPSH, the SAH extending northeastward to North China and the easterly jets prevailing in the high level over the MLYRV. In addi- tion, the summer LDFA in the MLYRV is of significant relationship with the Southern Hemisphere annual mode and the Northern Hemisphere annual mode in the preceding February, which offers some predictive signals for the summer LDFA forecasting in the MLYRV.

Relationship Between an Abrupt Drought-Flood Transition over Mid-Low Reaches of the Yangtze River in 2011 and the Intraseasonal Oscillation over Mid-High Latitudes of East Asia

NCEP/NCAR daily reanalysis data and Chinese daily gridded precipitation data are used to study the relationship between an aprupt drought-flood transition over the mid-low reaches of the Yangtze River in 2011 and the intraseasonal oscillation （ISO; 30-60 days） in the mid-high latitude meridional circulation of the upper troposphere over East Asia. The abrupt transition from drought to flood occurs in early June. The first two recovered fields of the complex empirical orthogonal function show that northward-propagating westerlies from low latitudes converge with southward-propagating westerlies from high latitudes over the mid-low reaches of the Yangtze River （MLRYR） in mid late May. The timing of this convergence corresponds to the flood period in early-mid June. The ISO index is significantly and positively correlated with rainfall over the MLRYR. During the dry phase （before the transition）, the upper troposphere over the MLRYR is characterized by cyclonic flow, easterly winds, and convergence. The regional circulation is dominated by a wave train with a cyclone over east of Lake Baikal, an anticyclone over northern China, and a cyclone over the MLRYR. During the wet phase, the situation is reversed. The configuration of the wave train during the dry phase favors the southward propagation of westerly wind disturbances, while the configuration of the wave train during the wet phase favors the development and maintenance of a pumping effect and sustained ascending motions over the MLRYR.

干旱区与湿润区旱涝急转演变特征对比研究

以长江、黄河和淮河流域为研究对象,基于标准化旱涝急转指数,利用趋势分析、变点检验、小波分析、随机森林等方法探究典型干旱区与湿润区旱涝急转演变特征及其驱动因子。结果表明:湿润和半湿润区是极端旱涝急转事件的高频发生区,干旱区是极端旱转涝事件的高频发生区;干旱区的突变发生在1998年,湿润区的突变在1978年,未来干旱区更易发生旱转涝事件,湿润区则相反;气象因子在湿润区对旱涝急转的贡献度更大,大气环流对干旱区的影响突出,旱涝急转与不同驱动因子间存在非线性关系。

近53 a辽河流域旱涝灾害的时空特征

针对气候变化背景下辽河流域旱涝事件的频繁发生,以国家气象中心提供的地面降水日值数据集V3.0为基础数据,采用Z指数法表征旱涝事件,并应用集合经验模态分解法(EEMD)分析了辽河流域1968—2020年逐年、逐生长季的旱涝事件分布特征及其周期性规律,结果表明:(1)辽河流域近53 a中发生旱涝事件的灾害年份约占总时间序列的2/3以上,集中发生于上世纪80、90年代中后期及本世纪00年代.(2)近53 a中,重度干旱或洪涝事件均以流域东南部的河流下游及入海口区域最为严重,流域东南部的旱涝程度反差最为强烈.(3)对于辽河流域范围的旱涝事件来说,周期特征以短时高频振荡为主,年代际尺度的波动对于周期规律的贡献率相对较低.

2022年7月内蒙古干旱半干旱区涝—旱转折事件的成因分析

2022年7月内蒙古中西部地区降水明显偏少,且呈前期偏多、后期偏少的涝—旱转折性分布特征,分析不同阶段环流分布差异和影响系统间的配置对进一步做好内蒙古汛期降水预测具有重要作用。利用内蒙古116站逐日降水量、国家气候中心130项气候指数、美国国家环境预报中心/国家大气科学研究中心(National Center for Enviromental Prediction/National Center for Atmospheric Research,NCEP/NCAR)逐日再分析资料和美国国家海洋和大气管理局(National Oceanic and Atmospheric Admin⁃istration,NOAA)逐月海表温度资料,分析2022年7月内蒙古中西部地区涝-旱转折事件的成因。结果表明:(1)2022年7月内蒙古中西部地区降水量严重偏少,为该地区1991年以来同期降水最少、气象干旱最为严重。(2)7月1—11日降水相对偏多,冷空气路径偏北且强度较弱,西太平洋副热带高压强度偏弱,位置偏北、偏西,冷暖空气在内蒙古中西部地区交绥,加之这一时段高空西风急流位置偏北,内蒙古中西部位于急流轴以南,有利于高层辐散和上升运动发展。7月12—31日降水明显偏少,环流经向度加大,冷空气活动路径偏南且强度增强,西太平洋副热带高压强度偏强且位置明显偏南,不利于水汽输送,加之高空西风急流位置偏南,内蒙古中西部位于急流轴以北,不利于高层辐散和上升运动发展;7月中旬后期至下旬高空西风急流南北向扰动偏强有利于激发东亚—西北太平洋经向遥相关波列,使得西太平洋副热带高压位置偏南从而导致降水偏少。(3)日本海至北太平洋西北部地区的海温异常是影响内蒙古中西部地区降水多寡的重要外强迫信号之一。2022年7月该海区海温异常偏高,其上空激发的气旋式环流减弱了南方暖湿水汽的经向输送,是导致内蒙古中西部降水由涝转旱的原因之一。

旱涝急转对玉米叶片衰老特性和产量的影响

为研究旱涝急转对玉米叶片衰老特性和产量的影响,以春玉米“宜丹629”为供试材料,2021年在测坑条件下,设置拔节期旱(drought,D)、涝(waterlogging,W)、旱急转轻涝(drought-light waterlogging,D-LW)、旱急转中涝(drought-moderate waterlogging,D-MW)、旱急转重涝(drought-heave waterlogging,D-HW)、和正常供水(control,CK)6个处理。测定不同处理组合下玉米大喇叭口期、抽雄期和灌浆期叶片叶绿素仪(soil and plant analyzer development,SPAD)值、过氧化物歧化酶(superoxide dismutase,SOD)、过氧化物酶(peroxidase,POD)、过氧化氢酶(catalase,CAT)活性、丙二醛(malondialdehyde,MDA)、可溶性蛋白含量和净光合速率(net photosynthetic rate,P_(n)),成熟期籽粒产量及其构成。结果表明,与CK相比,D-LW处理抽雄期和灌浆期玉米叶片的SPAD值、SOD、POD、CAT活性、可溶性蛋白含量、P_(n)和成熟期穗数、穗粒数和千粒质量差异不显著,其籽粒产量维持在较高水平(7 810.3kg/hm~2),说明旱急转轻涝不会加速玉米叶片的衰老,从而稳定籽粒产量。而其他水分胁迫处理显著降低各监测时期玉米叶片SPAD值、SOD、POD、CAT活性、可溶性蛋白含量和P_(n),明显提高MDA含量,使穗数、穗粒数和千粒质量减少,最终显著降低产量(较CK下降13.3%~72.7%)。整体上,D-MW和D-HW处理明显加速玉米叶片衰老,严重抑制籽粒产量。综上,拔节期旱后急转轻涝对玉米叶片SPAD值、抗氧化酶活性、可溶性蛋白含量和P_(n)有补偿作用,从而获得较高的籽粒产量。研究结果为玉米应对旱涝急转灾害和灌排管理提供理论依据。

长江流域旱涝急转演变特征及其社会经济暴露度

旱涝急转是指干旱和洪水之间的快速转变,对农业生产和人类安全造成巨大威胁。本研究基于月尺度的旱涝急转量级指数,分析了长江流域历史和未来四种旱涝急转事件,并通过滑窗法构建了旱涝急转量级的时变函数,揭示了未来旱涝急转风险变化。同时,结合共享社会经济路径量化了人口和经济受旱涝急转风险变化影响的程度。结果显示,历史时期长江流域中下游旱涝急转事件频发,旱–涝和涝–旱事件每10年发生10~12次,而旱–涝–旱和涝–旱–涝事件每10年发生3~4次。未来旱–涝–旱和涝–旱–涝事件预计大幅增加,其中长江上游部分地区增长了约7倍。对于历史基准期50年一遇的旱涝急转事件,未来发生概率将增加5~10倍,给长江流域的人口和经济带来重大影响。

中国旱涝急转事件时空变化特征

【目的】旱涝急转事件造成的社会经济和生态环境影响严重,是我国发生频繁且广泛的一种复合型事件。明确我国旱涝急转事件发生的时空变化特征,可为地区制定防灾减灾措施提供科学依据。【方法】基于1961—2021年气象观测数据,使用Penman-Monteith模型计算潜在蒸散发,然后计算逐日的标准化降水蒸散指数(daily-SPEI),分流域对中国旱涝急转事件的频次、影响范围和趋势的变化特征进行分析。【结果】结果显示:(1)时间趋势上,1961—2021年中国受旱涝急转事件影响的范围以0.6%/10a的趋势增加,且平均每年有19.8%的范围发生旱涝急转事件。(2)空间分布上,旱涝急转事件主要分布在淮河流域、黄河流域、长江流域和松花江流域,事件发生频次在30次以上地区分别占流域总面积的63.1%、20.7%、15.0%、14.6%,事件频次最高达到53次。(3)中国旱涝急转事件存在明显的季节差异,主要发生在夏季事件发生频次在5次以上的空间范围占中国总面积的一半以上;其次是春季和秋季,事件发生频次在5次以上的空间范围占比均不足15%;冬季发生最少,事件发生频次在5次以下。【结论】结果表明:中国旱涝急转事件的影响范围整体呈增加趋势,中国中东部和东北部是旱涝急转事件发生频繁地区。研究结果可为旱涝急转事件的监测与应对提供科学基础。

基于日尺度旱涝急转指数的重庆市旱涝急转事件演变特征分析

为准确地反映旱涝急转事件的“突发性”与“交替性”特征,对重庆市34个气象站采用日尺度旱涝急转指数DWAAI提取1960—2018年旱涝急转事件,根据重庆市的实际情况划分不同强度旱涝急转事件对应的DWAAI数值范围,探究不同强度旱涝急转事件发生频次的时空演变特征。结果表明:重庆市旱涝急转事件以旱急转涝为主,旱急转涝事件占旱涝急转事件累计次数的85%,主要发生在4—9月,多年平均次数为22.64站次,其中,中度、重度事件占所有旱急转涝事件的11.7%、2.9%;旱急转涝事件频发于重庆市西部、中部及东北部区域,发生频次的变化趋势不显著;涝急转旱事件主要发生在7—9月,多年平均次数为5.60站次,轻度、中度事件占所有涝急转旱事件的92.9%、7.1%;涝急转旱事件在重庆市东南部、中部以及东北部区域的西部地区(如开县)频发,频发地区的发生频次总体呈增加的趋势。研究成果可为保障重庆市及相关地区水安全、加强防旱抗涝减灾工作提供理论基础。

嘉陵江流域旱涝急转演变规律及其对径流影响研究

针对气象旱涝转换对流域径流影响的问题,基于嘉陵江流域逐日降水量和流量数据,采用长、短周期旱涝急转指数方法,揭示了旱涝急转时空分布特征与演变规律,定量评估了径流变化对不同旱涝急转类型的响应程度。结果表明:1977~2022年,嘉陵江流域共发生了8次汛期旱涝急转事件,其中6次发生在2004年及之后;空间上,南部、中部以及西北部地区发生旱涝急转的频率较大,在17%以上;在月尺度上,6~7月发生旱涝急转的频率最大,超过了20%。当汛期发生涝转旱时,北碚、罗渡溪、武胜以及小河坝等站的前半汛期流量相比常年平均增长了57.52%,38.74%,85.50%和99.73%,后半汛期流量相对常年平均偏低了20.82%,49.83%,22.64%和14.53%;而在旱转涝影响下,上述站点前半汛期流量较常年平均减少了31.17%,45.77%,28.83%和26.16%,后半汛期流量较常年分别增长了31.45%,47.17%,24.31%和3.27%;月尺度上也表现出相似规律,表明旱涝急转对嘉陵江径流有着显著影响。研究成果可为梯级水库科学调度、流域水安全保障提供参考。

辽宁省旱涝急转特征与趋势研究

【目的】旱涝急转事件有较高的突发性和致灾性,明确辽宁省旱涝急转的特征与趋势,为辽宁省旱涝灾害预警与水资源应急管理提供依据。【方法】旱涝急转指标是进行旱涝急转研究的基础,利用辽宁省19个气象站点1970—2020年的降水数据,分别采用长、短周期旱涝急转指数(LDFAI、SDFAI)进行时空特征分析,并指明旱涝急转指数的异同,实现对辽宁省旱涝急转事件的量化识别。【结果】结果表明:(1)1970—2020年辽宁省LDFAI与SDFAI总体呈上升趋势,未来辽宁省干旱转洪涝风险正逐步提升;(2)辽宁省旱涝急转事件的发生概率空间差异性显著并且与辽宁省的降水分配不均密切相关;(3)SDFAI重心变化幅度明显大于LDFAI,LDFAI与SDFAI迁移中心主要集中在辽宁省中部盘锦、鞍山、营口等地。【结论】总体来看,辽宁省旱涝急转现象频发,且具有周期性,强度逐年增大。研究结果可为辽宁省科学应对旱涝灾害和提高水资源应急管理能力提供参考。

水稻品质及产量对灌浆期旱涝急转的响应

为探究灌浆期旱涝急转对水稻品质及产量的影响,以湘早籼6号为研究对象,基于桶栽试验,采用四因素三水平正交试验设计,设置干旱水平(田间持水量的65%±5%,50%±5%,35%±5%)、干旱历时(5,7,9 d)、淹涝水平(淹没株高的50%,75%,100%)、淹涝历时(5,7,9 d),共计9个旱涝急转处理,以及对照处理(CK),探究灌浆期旱涝急转下各水稻品质指标及产量的响应规律,并在主成分分析基础上,通过理想点法技术(TOPSIS)对产量及品质的综合质量进行评价.结果表明:灌浆期旱涝急转会导致米粒偏短、偏窄,透明度与黄粒米率显著提高,垩白度与垩白粒率分别较CK提高了13.42%~69.16%和6.14%~48.72%;直链淀粉质量分数在灌浆期旱涝急转下较CK提高12.39%~34.46%,而胶稠度的降低幅度为25.26%~36.84%;除碱消值外,灌浆期旱涝急转下的水稻品质受干旱和淹涝的共同影响,淹涝水平是大部分品质指标的主要影响因素;与对照相比,灌浆期旱涝急转导致水稻减产67.32%~98.71%,大部分品质指标与产量呈负相关,长宽比与产量的负相关性最强(r为-0.78***),胶稠度与产量呈正相关(r为0.68***);灌浆期旱涝急转下水稻产量及品质的综合质量最优的处理为轻旱轻涝急转,综合质量最差的处理为重旱重涝急转.研究结果可为应对旱涝急转的水稻品质改良以及减灾策略的制定提供理论依据.

旱涝急转工况下土石坝上游粘土防渗体水力劈裂研究

近年来作为极端小概率事件的旱涝急转工况频繁出现,极易造成防渗体缺陷扩展,诱发工程失事。通过在模型试验与数值计算分析的基础上探讨了旱涝急转工况下土石坝粘土防渗体中的水力劈裂问题。结果表明,旱涝急转工况中的干旱过程促使土体基质渗透性降低,同时导致防渗体产生裂缝,具备了发生水力劈裂的必要条件。理论分析推导了沿裂缝所在平面产生水力劈裂破坏的渗透压力理论值,离心试验模型测得铺盖层孔压骤降的同时砂层孔压骤增,表明裂缝受高水压作用产生劈裂贯穿了防渗体,裂缝处测量孔隙水压力值与理论推导结果基本一致。旱涝急转过程中裂缝处土体内的压应力先是逐渐增大,随后不断减小最终转变为拉应力,从而导致水力劈裂。研究结果对旱涝急转工况下的土石坝安全运行具有指导作用。

旱涝急转条件下水稻水分利用效率变化研究

为探究水稻在旱涝急转条件下光合效率及水分利用变化规律,从而为研究水稻经历旱涝急转灾害后产量变化及灌溉方式提供科学依据,以Ⅱ优898水稻为研究对象,采用四因素三水平正交实验,研究了旱涝急转条件下,水稻叶片水分利用效率WUE_(leaf)及气孔导度gs、蒸腾速率E、光合速率A等参数的变化。结果表明干旱程度和淹水深度对光合作用的累积作用最明显;A/gs与叶气温差呈线性相关,但旱涝急转导致响应积极性降低;分蘖期末~拔节孕穗期初WUE_(leaf)~g_(s)均可用上凸抛物线描述,此阶段干旱引起绝对光合速率的降低是影响生育期生物量积累的控制因素。拔节孕穗中后期WUE_(leaf)~g_(s)均可用下凸抛物线描述,经历旱涝急转导致叶片提前衰老,绝对蒸腾速率下降,WUE_(leaf)的增加并不能促使产量的补偿,可提前控制土壤含水量,减少非必要的水资源消耗。

川渝高温热浪与暴雨旱涝演变特征及适应策略研究

为加深对川渝地区多灾种综合影响的理解,提升灾害综合风险防范能力,基于长时序观测数据,利用线性拟合、Pettitt检验、小波时频分解等方法,分析了1961~2022年川渝热浪与暴雨的时空演变特征,并针对耦合影响区提出适应性策略。结果表明:(1)近60 a来川渝总体高温热浪趋强趋长趋频,且不同时长高温热浪的区域差异性特征显著。川南经济区、川东北经济区至重庆市9 d及以上高温热浪的发生频次显著增多,成都平原经济区西部3~8 d高温热浪频次显著增多,自1990年代初期以来,盆西变化尤为明显。(2)川渝暴雨灾害变化也存在显著的区域差异。成都平原经济区西部、川南经济区暴雨日数显著减少、强度降低,川东北经济区至重庆市的暴雨日数增加、强度增强。(3)对高温干旱复合与旱涝急转事件的分析表明,盆东至重庆市旱涝急转自1980年代中期以来显著增加,盆南高温干旱复合事件自2000年代初以来显著增加。(4)成都平原经济区应着重关注高温热浪频发对超大城市脆弱人群及能源供给的冲击;川南经济区需关注持续性高温热浪叠加干旱给工业、农业带来的不利影响;川东北经济区在充分考虑高温热浪和暴雨灾害单独影响的同时,也应进一步综合考虑区域内旱涝急转给农业及重点项目带来的不利影响。

1976—2020年弥河流域旱涝急转特征分析

基于弥河流域13个雨量站1976—2020年的逐日降水数据,使用长周期旱涝急转指数(LDFAL)、短周期旱涝急转指数(SDFAL),通过Mann-Kendall趋势检验、Mann-Kendall突变检验、滑动T检验、重标极差分析法(R/S分析法)、小波分析法、反距离插值法对弥河流域旱涝急转的时空分布特征进行分析。结果表明:在45 a内,弥河流域长周期6—9月共发生18次旱涝急转现象,LDFAL呈现下降趋势,表明未来“旱转涝”现象将占据主导。SDFAL在6—7月和8—9月呈现上升趋势,表明未来“涝转旱”现象将占据主导;7—8月呈现下降趋势,表明未来“旱转涝”现象将占据主导。LDFAL与旱涝急转强度均未发生突变,SDFAL只在2007年6—7月发生突变,短周期旱涝急转强度在2007年的6—7月和2005年的7—8月发生突变。长周期旱涝急转现象变化存在11 a主周期,短周期6—7月、7—8月、8—9月的变化主周期分别为34、64、43 a。

湖北省旱涝灾害致灾规律的初步研究

利用1960—2005年湖北省76个地区气象灾害的灾情普查数据和逐日降水量观测资料,对湖北省旱涝灾害的时空分布特征及其致灾规律进行分析。结果表明:干旱灾害的频发区呈东西走向的带状分布,而洪涝灾害的发生频次和频发区面积均明显少于干旱;干旱和洪涝灾害年平均发生站次在1996年以后出现相反的变化趋势,干旱发生站次增加,而洪涝发生站次减少,且两种灾害均主要集中发生在夏季;1996—2001年湖北省部分地区连续出现严重干旱灾害,干旱的累积增强效应导致农业经济损失出现跳跃性增长并在2001年达到最大值;洪涝的致灾强度呈准周期的起伏振荡,农作物受洪涝影响面积最大、损失最多的年份集中在20世纪90年代,农作物受害面积与农业经济损失的决定系数为0.8;受害人口与直接经济损失具有较好的相关特征,且直接经济损失随受害人口增多而增加的速度加快,但近年来人口对洪涝灾害的抵御能力也显著提高;急转干旱和急转洪涝主要发生在鄂西北和鄂东南的夏季,农作物的脆弱度增加,农业经济损失随受害面积增大而增加的速度加快,但所造成的农业经济损失远小于仅发生干旱和洪涝时的数值。