Numerical Study of Ural Blocking High＇s Effect Upon Asian Summer Monsoon Circulation and East China Flood and Drought

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DIAGNOSTIC ANALYSIS OF PERSISTENT DROUGHT/FLOOD EVENTS IN SUMMER OVER THE TWO-LAKE REGION OF CHINA

Based on the daily regional mean rainfall,the Z-index method is used to identify persistent flood and drought events lasting for at least 10 days over a region where Dongting Lake and Poyang Lake sit(referred to as the"two-lake region"hereafter).The National Centers for Environmental Prediction(NCEP)reanalysis data are then utilized to perform a preliminary diagnostic analysis on these events.The results indicate that the composite standardized geopotential height at 500 hPa presents two different meridional wave trains from north to south over the East Asian-Pacific region,i.e.,a"-+-"pattern for the droughts and a"+-+"pattern for the floods,respectively.The developing,maintaining and decaying phases in the drought and flood events are closely related to the intensity and location of a subtropical high and an extra-tropical blocking high.It is shown that the East Asian summer monsoon is strong(weak)with the occurrence of persistent drought(flood)events.Droughts(floods)are accompanied by a weak(strong)tropical convergent system and a strong(weak)subtropical convergent system.Furthermore,the persistent drought(flood)events are associated with a divergence(convergence)of vertically integrated water vapor flux.In the vertical profile of water vapor flux,divergence(convergence)in the mid-and lower-levels and convergence(divergence)in the higher levels are evident in the droughts(floods).Both the divergence in the droughts and the convergence in floods are strongest at 850 hPa.

Effects of spring Arctic sea ice on summer drought in the middle and high latitudes of Asia

本文分析了亚洲中高纬度地区(MHA)年际尺度夏季干旱的主模态时空变化特征,以及影响第一模态的主要影响因子和可能的物理过程.结果显示该区域夏季干旱第一模态主要呈现一个南北偶极性的分布.而影响MHA夏季干旱的主要影响因子为前春北极海冰.当春季斯瓦尔巴群岛附近海冰偏多,而巴伦支海-喀拉海海冰减少时,通过冰-气相互作用,使得MHA北部春季降水增加,雪深加厚,土壤湿度偏高,而南部则相反.然后这样的土壤湿度条件从春季持续到夏季,通过土壤湿度-大气反馈影响夏季MHA降水和温度变化,最终对夏季干旱主模态产生影响.

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 1950 s 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.

Discussion on the Causes of Drought in Summer in Alashan League in 2010

[Objective] The causes of drought in summer in Alashan League in 2010 were discussed. [Method] Through the discussion of climate background, circulation characteristics, subtropical high and ocean temperature of the severe drought in Alashan League in Inner Mongolia during the flooding time, the potential causes of drought in Alashan League in summer in 2010 were discussed. [Result] The circulation around Alashan League and surroundings in 850 hPa was weak. Especially the southerly was extremely weak and it restricted the transportation of southerly water vapor towards Inner Mongolia, which was one of the direct reasons of drought; the 500 hPa high pressure ridge controlled Alashan League, and resulted into long-term drought and lasting high temperature. The summer seasonal wind was weak and arrived land in Alashan League. The northwest pacific subtropical high was large and strong. Only when subtropical high was strong and merged as well as strengthened with high pressure ridge around middle and high latitude in the lower reaches 130°-140° E, can rain be generated. However, the latter condition was limited in summer in 2010. When the ocean temperature around 30°-50° N and 140°-150° E was low in the north and high in the south, there would be less rain in Alashan League. [Conclusion] The study provided relevant information and technological support for the drought disaster warning forecast, drought observation system, and disaster prevention and mitigation measures.

Drought and Waterlogging Characteristics during the Growth Period of Summer Maize in Luxi Plain Areas

In summer maize growth period,the water supply and demand ratio is regarded as the evaluation index of drought and waterlogging for the summer maize in Liaocheng City. Using GIS,statistics,agrometeorology and other methods,we analyze the precipitation during the summer maize growth period in Luxi Plains from 1961 to 2011. Through the calculation of drought and waterlogging index,it indicates that the disasters of drought and waterlogging frequently occur during the summer maize growth period,mainly affected by the drought; the frequency of occurrence of drought accounts for 80. 4%,that is,it is very prone to serious drought phenomenon,seriously affecting the normal growth and development of summer maize during the seedling period. With global warming,the industrial and domestic water demand is increasing year by year,so it is extremely difficult to increase the water diversion to solve the problem of water shortage for the growth of summer maize. Finally we put forth the following recommendations:( i) Selecting drought-resistant varieties,and improving the water resource use efficiency;( ii)Promoting the water and fertilizer coupling,sprinkler irrigation,drip irrigation,micro-irrigation and other water-saving irrigation technologies,and improving the water use efficiency;( iii) Promoting the ditch,ridge and laminating cultivation technology,reducing the field evapotranspiration,keeping warming and conserving moisture,and saving water resources;( iv) Strengthening the construction of water conservancy facilities,so that it can be irrigated during drought and drained during waterlogging;( v) During dry season,timely organizing artificial rainfall operation,and increasing precipitation in arid areas to ease drought;( vi) Rationally exploiting the groundwater,and improving the underground water use efficiency.

Study on the Strengths and Weaknesses of Agricultural Climate Resources during Summer Drought in Guizhou Province

In order to quantitatively assess the objective impact of light,heat and water agricultural climate resources on food crops during summer drought,this paper uses the assessment methods for light and temperature potential productivity,and light,temperature and water potential productivity of food crops,performs the comparative analysis of the difference between the food production potential and the average climate state during summer drought,and objectively analyzes the strengths and weaknesses of agricultural climate resources in Guizhou Province during summer drought. Studies show that under summer drought in Guizhou Province,the light and temperature potential productivity of rice and corn is generally about 10% higher than in normal climate years,and the strengths of light and heat resources are obvious; the light,temperature and water potential productivity of rice and corn is generally 30% to 40% lower than in normal climate years,and the weaknesses of water resources hamper the crop growth. Rational development and efficient use of water resources and good light and heat conditions for crops during drought,are more conducive to agricultural production.

Analysis on the Disastrous Weather of Serious Drought in Northwest Hunan in Summer and Autumn of 2009

[Objective] The research aimed to analyze the disastrous weather of serious drought in Northwest Hunan in summer and autumn of 2009.[Method] According to the meteorological data in Zhangjiajie of Northwest Hunan during the drought period from June to September,2009,the disaster characteristics of continuous drought in summer and autumn were analyzed.Based on NCEP/NCAR 2.5°×2.5° reanalysis data,by using the climatic diagnostic method,the formation reason of serious drought was initially analyzed from the circulation characteristics in the middle and high latitudes,Western Pacific subtropical high,the abnormal characteristics of sea surface temperature in the equatorial Middle Eastern Pacific Ocean and the tropical system activity.[Result] The characteristics of serious drought in Northwest Hunan in summer and autumn of 2009 were the quick developed speed,wide influence range,long duration,big disaster loss and long high temperature time.The influence range,duration and harm degree were rare to see in the history.During the arid period(June-September),the atmospheric circulation was abnormal.The polar vortex in the northern hemisphere was weak,and the center was by north.It was two-trough-one-ridge type in the middle and high latitudes of Eurasia.The long-wave trough existed respectively near Balkhash Lake and from Sea of Okhotsk to the east coast in China.The long-wave ridge maintained from Lake Baikal to Central Asia and stabilized in 90°-110° E of Central Asia.From the middle dekad of June to the middle dekad of September,the westerly index increased.The zonal circulation was the main one in the middle and high latitudes of Eurasia.The cold air in the high-latitude frontal zone spread eastward with the small-amplitude fluctuation form along the latitude circle direction,and was difficult to pass the westerly barrier near 45° N to reach the low latitude.Meanwhile,Western Pacific subtropical high jumped northward to control Jiangnan and South China for a long time.The down airflow was prevalent.It was hot and rainless.The drought developed quickly.The sea surface temperature in the equatorial Middle Eastern Pacific Ocean started to rise in June,and it entered into El Nino state.When El Nino event of obvious temperature increasing started to appear in spring and summer,the plum rain amount was less in the middle and low reaches of Yangtze River in the year or next year.The probability was 80%.In El Nino year,the typhoon was less.In addition,for the influence of strong Western Pacific subtropical high,the landing pathway of typhoon was by east or south.The kind of typhoon had the small role for easing the drought in Northwest Hunan.[Conclusion] The research provided the theory basis for improving the prediction level of short-term climate and the understanding of extreme climate event.

Differences in physiological and biochemical responses to summer drought of Pinus nigra subsp.pallasiana and Pinus brutia in a natural mixed stand

Understanding how tree species respond to drought in their natural environment is needed to predict forest adaptation and management practices under global environmental changes.This study was carried out to determine and compare physiological and biochemical responses to variations in environmental conditions during summer drought of mixed natural stands of Pinus nigra Arn.subsp.pallasiana(Lamb.)Holmboe and Pinus brutia Ten.Midday xylem water potential(ψmd),water relations,photosynthetic pigments,total soluble sugar and proline contents were investigated during the growing season.ψmd followed a similar seasonal trend in both species but P.nigra subsp.pallasiana had higher ψmd than P.brutia.The ψmd gradually decreased from June,reached its lowest value in August,and then increased again.Gradual decreases in the osmotic potential at turgor loss point(ψnTLP)were observed during the summer.Generally,ψnTLP was lower in P.brutia.Total soluble sugars decreased from April to June for P.brutia,then increased and stayed relatively constant August to October.Similar changes were found at lower values in P.nigra subsp.pallasiana.Prolin accumulation and photosynthetic pigments were higher in P.brutia.The results indicate that physiological and biochemical responses of both species against changing environmental conditions were in different degrees but followed similar trends.P.nigra subsp.pallasiana is more sensitive to summer drought than P.brutia in their natural environment.

DIAGNOSES OF THE SEVERE DROUGHT OVER YUNNAN AREA IN THE EARLY SUMMER OF 2005

High temperature and drought occurred in Yunnan province during the late spring and early summer in 2005, which was the most severe event in this region since 1950’s. Based on the observational data and relevant diagnoses, this extreme weather event was studied and discussed. The results show that the occurrence of this event could be due to the following observational facts that happened in 2005. (1) The seasonal adjustment of middle-high-leveled atmospheric circulation was delayed. (2) The cold air activity center was deviated north. (3) The onset of summer monsoon over South China Sea was delayed. (4) The tropical convection activity was much weaker than usual. (5) The subtropical high over the western Pacific was located southwestwards and relatively strong.

干旱条件下淮北平原夏玉米根系水分来源研究

为探究干旱胁迫条件下淮北平原夏玉米生长期水分利用特征,分析农田降水-土壤水-作物水之间的转化规律。通过野外实验和室内分析,测定分析不同生长期内降水、土壤水、植物水、地下水的稳定氢氧同位素值。采用稳定氢氧同位素技术分析了各水体的同位素分布特征,利用直接对比法和多元线性混合模型法分析夏玉米对土壤水分的主要吸水深度及贡献率,进而研究其水分来源。结果表明,五道沟实验站夏季大气降水线方程为δD=7.26×δ^(18)O+3.11(R^(2)=0.98),其斜率和截距均小于全球大气降水线方程,表明降水在降落过程存在蒸发富集过程。土壤水氢氧同位素在垂直方向剖面呈现明显的梯度分布。干旱胁迫条件下,夏玉米拔节-抽雄期主要吸收0~20、20~40、40~60 cm处的土壤水,贡献率分别为21.8±13.6%、25.5±20%和25.1±18.2%;抽雄-灌浆期主要吸收0~20 cm处的土壤水,贡献率为68.6±3.6%;灌浆-成熟期主要吸收0~20 cm处的土壤水,贡献率为72.0±0.9%。夏玉米根系优先利用浅层土壤水,土壤水主要来自大气降水。地下水埋深较浅地区,干旱条件下夏玉米在整个生长期内根系吸水深度较浅,由此考虑生长期改变灌溉方式来提高灌溉水利用率。

河南省夏玉米不同生长阶段干旱风险分析

【目的】研究夏玉米各生长阶段的抗干旱风险,为预防夏玉米受干旱影响导致产量和品质下降,降低干旱造成的损失提供理论依据。【方法】本研究利用河南省16个气象站1981—2019年的逐日气象数据,以作物水分亏缺指数(CWDI)为评判指标,根据《北方夏玉米干旱等级》(QX/T 260—2015)对该地区玉米5个生长发育时期进行了干旱等级划分,分析各等级干旱发生的频率、干旱风险指数的时空分布规律。【结果】河南省夏玉米各生长阶段干旱发生总频率在豫北地区最高,其次是豫中和豫东。干旱发生总频率均在夏玉米抽雄—乳熟期最大,高达96%以上,且以中旱和特旱为主。不同等级干旱发生的频率具有差异性,但豫南地区各生长阶段各等级干旱发生的频率相对较低。在夏玉米播种—出苗、出苗—拔节期,河南省各地区干旱风险指数呈由南向北逐渐增加的空间分布特征;在拔节—抽雄、抽雄—乳熟和乳熟—成熟期,该指数基本在30以上。【结论】各地区夏玉米在拔节—抽雄、抽雄—乳熟和乳熟—成熟期干旱发生的风险均较高。夏玉米各个生长阶段干旱发生的风险均为豫北地区最高,豫南地区最低。应重点关注豫北地区的防旱减灾工作。

四川盆地东部再生稻高温伏旱区腋芽萌发期气象适宜度

以四川盆地东部再生稻高温伏旱区为研究区,基于气象条件对腋芽萌发期再生稻生长发育的影响机理,采用结构方程模型探明了腋芽萌发的影响因素、影响路径及影响强度。进一步结合隶属函数和层次分析法,构建了再生稻腋芽萌发气象适宜度模型,并分析了1981—2021年研究区腋芽萌发期气象影响因素及气象适宜度的变化特征。结果表明:气温、空气湿度、降水是四川盆地东部再生稻高温伏旱区腋芽萌发的关键影响因素,基于以上因素的气象适宜度模型能较好地评价再生稻腋芽萌发期的气象影响。1981—2021年研究区气温适宜度、空气湿度适宜度及综合气象适宜度均呈下降趋势,降水适宜度没有表现出明显的变化趋势。气温适宜度、空气湿度适宜度及综合气象适宜度总体呈“西高东低”的空间分布特征,降水适宜度则表现为“东西高、中部低”。1981—2021年研究区气温上升趋势与空气湿度下降趋势显著,导致致害高温(日平均气温≥32℃)积温和致害低湿(日平均相对湿度≤65%)日数明显增加,这是再生稻腋芽萌发期气象适宜度总体呈下降趋势的诱因。

宁波市2022年夏季旱情分析及对策建议

2022年出梅后,宁波市受西太平洋副热带高压中心控制,遭遇3轮大范围、持续性的罕见高温天气,高温少雨导致宁波市各区(县、市)均发生了不同程度的旱情,9月初,受2211号台风“轩岚诺”降雨影响,干旱解除。通过研究宁波市2022年夏季干旱成因及旱情等级评估,并与历史同期旱情进行对比分析,提出旱情灾害防御相关对策建议,为其他地区发生类似旱情提供决策参考。

THE DIRECT EFFECTS OF AEROSOLS AND DECADAL VARIATION OF GLOBAL SEA SURFACE TEMPERATURE ON THE EAST ASIAN SUMMER PRECIPITATION IN CAM3.0

Using the CAM3.0 model, we investigated the respective effects of aerosol concentration increasing and decadal variation of global sea surface temperature(SST) around year 1976/77 on the East Asian precipitation in boreal summer. By doubling the concentration of the sulfate aerosol and black carbon aerosol separately and synchronously in East Asia(100-150 °E, 20-50 °N), the climate effects of these aerosols are specifically investigated. The results show that both the decadal SST changing and aerosol concentration increasing could lead to rainfall decreasing in the center of East Asia, but increasing in the regions along southeast coast areas of China. However, the different patterns of rainfall over ocean and lower wind field over Asian continent between aerosol experiments and SST experiments in CAM3.0 indicate the presence of different mechanisms. In the increased aerosol concentration experiments, scattering effect is the main climate effect for both sulfate and black carbon aerosols in the Eastern Asian summer. Especially in the increased sulfate aerosol concentration experiment, the climate scattering effect of aerosol leads to the most significant temperature decreasing, sinking convection anomalies and decreased rainfall in the troposphere over the central part of East Asia. However, in an increased black carbon aerosol concentration experiment, weakened sinking convection anomalies exist at the southerly position. This weakened sinking and its compensating rising convection anomalies in the south lead to the heavy rainfall over southeast coast areas of China. When concentrations of both sulfate and black carbon aerosols increase synchronously, the anomalous rainfall distribution is somewhat like that in the increased black carbon concentration aerosol experiment but with less intensity.

Atmospheric Blocking in the South Atlantic during the Summer 2014: A Synoptic Analysis of the Phenomenon

Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a positive anomaly of the air pressure. As a result, in the regions affected by the blocking occur several consecutive dry days and temperatures above average. This paper aims to discuss synoptically the atmospheric blocking phenomenon occurred in January and February 2014 in the South Atlantic Ocean, affecting especially the Southeastern Brazil and sectors that depend on the quantity of water for their activities in the region, such as agriculture and electricity generation. The significant population concentration makes this area emphatically vulnerable to long periods of drought, especially during the summer, affecting the water supply for the population. In order to achieve this goal, data of geopotential height at 850/500 hPa, streamlines in 850/500 hPa, pressure, temperature, humidity and wind at surface were evaluated through NCEP/ NCAR reanalysis (CFSRv2—Climate Forecast System Reanalysis Version 2) with 0.2&#176 × 0.2&#176 resolution. The analysis showed that the stationary anticyclone was configured dynamically favorable to blocking in the lower and middle levels of the atmosphere. Thus, atmospheric pressure at mean sea level presented values above normal combined with high average air temperature. By the climatological analysis, it was noted that there were emphatic negative precipitation anomalies over Southeastern Brazil. This atmospheric blocking was characterized as anomalous due to its long duration in a considered rainy season.

Relation among Summer Rainfall in South Shandong and High Pressure in South Asia and Atmospheric Circulation

[Objective] The aim was to study the relation among summer rainfall in south Shandong and high pressure in South Asia and atmospheric circulation.[Method] Taking the precipitation in south Shandong along the Yellow River and Huaihe River,using the NCEP/NCAR data and summer rainfall data in south Shandong in summer from 1961 to 2005,the characteristics of high pressure in South Asia and atmospheric circulation in drought year and flood year in summer in south Shandong Province were expounded.The mechanism of 100 hPa pressure in South Asian influencing precipitation in south Shandong Province was discussed.The interaction of different equipment,different altitude and different system of atmosphere circulation in low and high layer was expounded.[Results] The first mode of EOF decomposition of precipitation in summer in south Shandong Province explained above 63% variances and reflected universal form of precipitation.The difference of central position of the central position of height field of high pressure in South Asia in drought and flood year was small.But the wind field center was inconsistent.As the area of SAH was smaller and its eastern ridge line stretched to the Western Pacific between the middle of south Shandong and Changjiang Estuary,flood summer occurred when there was an unusual cyclone lied in the east of 90° E and south of Lake Baikal.The area of SAH was larger and its eastern ridge line stretching to the Western Pacific over Changjiang Estuary,drought summer occurred,when there was an unusual anticyclone lied in the east of 90° E and south of Lake Baikal.SAH and summer rainfall also had close relationship with Tele-connection Patterns over the Eurasia continent and EAP Tele-connection.When the height anomaly was in "+-+" form in the north of the Caspian Sea,around Lake Baikal and Kamchatka,and when the height anomaly in East Asia-West Pacific area was in "-+" form from low altitude to high altitude,there was much precipitation in summer;and conversely,it was drought in summer in south Shandong.[Conclusion] It provided the oretical basis for summer rainfall in south Shandong.

Premature losses of leaf area in response to drought and insect herbivory through a leaf lifespan gradient

Implications of the differences in leaf life span are still subject to debate in the field of ecophysiology.Since leaf traits associated with these differences may be decisive for determining the distribution of tree species,this topic is particularly relevant in the context of climate change.This study analyzes the effects of the differences in leaf life span on premature losses of leaf area owing to insect herbivory and to abiotic stress.Loss of leaf area may be an important determinant of total leaf carbon assimilation.Seven Mediterranean tree species,distributed on four sites with different climates were studied.The species exhibited strong differences in leaf life span and in leaf traits,especially leaf mass per unit area.Premature leaf area losses were estimated in response to insect herbivory and summer drought over two years.The results revealed that,despite having older leaf cohorts with more damage,species with longer leaf duration had lower area lost to herbivores and less damage due to accelerated senescence during the summer drought.With respect to the predicted increase in water stress,deciduous species are at a disadvantage due to their high premature loss of leaf area and thus loss of photosynthetic capacity.

2022年长江流域夏秋旱特点分析与思考

近年来,极端天气事件呈现趋多、趋频、趋强、趋广态势,干旱灾害的极端性、反常性越来越明显,干旱灾害风险的复杂性、多变性也愈来愈显著。2022年,水资源相对丰沛的长江流域发生1961年有完整记录以来最严重的气象水文干旱,影响波及流域农业生产、城乡供水、生态、航运、发电等诸多方面。在总结2022年长江流域旱情、旱灾特点的基础上,分析长江流域抗旱减灾工作中存在的难点及问题,并有针对性地提出了未来抗旱减灾工作重点的建议。

连旱对夏玉米叶绿素荧光特性、产量和水分利用效率的影响

【目的】探明连续干旱胁迫对夏玉米叶绿素荧光特性、产量和水分利用效率(WUE)的影响,为夏玉米抗旱稳产提供理论指导。【方法】选用夏玉米“DHA757”为供试品种,在拔节期(B)、抽雄期(C)和灌浆期(G)设置不同程度的干旱处理,分别为:正常(CK)、轻旱(1)、中旱(2)、重旱(3),分别对应田间持水率(FC)的(70%,80%)、(60%,70%)、(50%,60%)、(40%,50%)。通过移动防雨棚下桶栽的方式控水,试验设置拔节期单旱2个,两阶段连旱(拔节—抽雄期)3个,三阶段连旱(拔节—抽雄—灌浆期)3个,研究了连旱胁迫对夏玉米耗水量、SPAD、Fv/Fm、Fv/Fo、产量和WUE的影响。【结果】与CK相比,连旱胁迫显著降低了夏玉米的耗水量、SPAD、Fv/Fm和Fv/Fo,且降幅随干旱程度的加剧而增大。不同干旱处理均会造成夏玉米减产,在拔节期单旱处理下,B3减产最明显,B2次之;两阶段连旱和三阶段连旱处理下,轻旱减产不明显,其他干旱程度均导致产量显著降低。WUE在B2、B1C1、B2C2处理下相比CK分别增加了5.1%、2.8%、6.3%,说明低程度干旱有助于WUE的提高。【结论】综合考虑产量和WUE,拔节期中旱(50%~60%FC)和拔节—抽雄期两阶段连续轻旱(60%FC~70%FC)是节水和保障粮食安全的适宜选择。