Flowering Characteristics of Japonica Rice Male Sterile Lines Adaptive to High Temperature and Summer Drought

[Objective] This study was conducted to screen japonica rice male sterile lines with good flowering characteristics under high temperature and summer drought. [Method] The flowering habits of 23 japonica male sterile lines, such as flowering peak, single-panicle flowering duration, single-plant flowering duration, en- closed glume rate, glume-opening angle, the distance between glumes, stigma exer- tion rate and sigma vitality, were compared with II-32A as a control under above weather condition. [Result] The flowering characteristics had significant difference a- mong the tested rice lines. Compared with the control, three japonica rice male ster- ile lines 35478A, 35489A and 35502A had better flowering traits, such as earlier flowering peak, longer single-panicle flowering duration, longer single-plant flowering duration, lower rate of enclosed glumes, larger glume angle and larger distance be- tween glumes. 35478A performed its flowering peak from 10：00-11：00 am, 1.5 h earlier than the control; 35489A exhibited higher stigma exertion rate, up to 76.23%; and 35502A had higher stigma vitality, up to 84.68%, which kept longer time than that of the CK. [Conclusion] The results will provide high-quality resources for the breeding of new japonica rice varieties with high-yield and high-temperature toler- ance.

Analysis on the Climate Characteristics of Summer Drought Frequency in Chongqing

By using daily meteorological data from 34 surface meteorological stations in Chongqing from 1960 to 2006,the climate characteristics of summer drought in recent 47 years were analyzed by means of Morlet wavelet analysis.The results revealed that summer drought in Chongqing showed obvious decrease trend on the whole,while extreme severe summer drought decreased firstly and then increased,especially since 1990s with obvious increase trend.Around 1995 or 2004,there existed obvious oscillation period of 2-3 years in summer drought in Chongqing,and extreme severe summer drought was very stable without evident oscillation in 1906s,while there was obvious strong oscillation period of 4-5 years in extreme severe summer drought in Chongqing from 1970 to 1978.

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

Based on data observed from 1979 to 2017,the influence of Arctic sea ice in the previous spring on the first mode of interannual variation in summer drought in the middle and high latitudes of Asia(MHA)is analyzed in this paper,and the possible associated physical mechanism is discussed.The results show that when there is more sea ice near the Svalbard Islands in spring while the sea ice in the Barents-Kara Sea decreases,the drought distribution in the MHA shows a north-south dipole pattern in late summer,and drought weakens in the northern MHA region and strengthens in the southern MHA region.By analyzing the main physical process affecting these changes,the change in sea ice in spring is found to lead to the Polar-Eurasian teleconnection pattern,resulting in more precipitation,thicker snow depths,higher temperatures,and higher soil moisture in the northern MHA region in spring and less precipitation,smaller snow depths,and lower soil moisture in the southern MHA region.Such soil conditions last until summer,affect summer precipitation and temperature conditions through soil moisture–atmosphere feedbacks,and ultimately modulate changes in summer drought in the MHA.

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.

Climate Characters of Summer Drought in Mountain City and the Effect on Flowers and Trees

[Objective] The aim was to provide references for development of industries engaging in flowers and trees in Beipei area in Chongqing. [Method] The occurring trend, intensity trend of summer drought, relationship of intensity with rainfall and extremely highest temperature, occurring trend during initial period of summer drought and the effects in mountain cities were analyzed, based on information on lasting period, rainfall, average temperature, extremely highest temperature of sum- mer drought in Beipei area in mountain cities during 1981-2010 and, growth condi- tion and phenological phenomena of Michelia champaca during 2005-2007. [Result] The occurring probability of summer drought in mountain cities was 57% and the probabilities of light, moderate, heavy and extreme drought were 30%, 10%, 7% and 10%; intensity of summer drought was none of linear relation with rainfall and ex- tremely highest temperature. In summer drought, daily average rainfall was less than 0.9 ram; extremely highest temperature was 35.0-45.0 ℃ with probability at 30%; initial period of summer drought was from later June to middle August and of extreme drought was later June-later July; the ending period was early September. During drought, when the extremely highest temperature （〉35.0 ℃） occurred in three days within a Hou, flowers and trees were affected by the hot drought and when the extreme temperature （〉40.0 ℃） occurred in three days within a Hou, the plants were seriously affected. [Conclusion] Based on characters of summer drought, pre- cautions can be taken to reduce effects of summer drought on flowers and trees with the help of weather forecast.

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.

The Relation between Atmospheric Intraseasonal Oscillation and Summer Severe Flood and Drought in the Changjiang-Huaihe River Basin

The intraseasonal oscillation (ISO) is studied during the severe flood and drought years of the Changjiang-Huaihe River Basin with the NCEP/NCAR reanalysis data and the precipitation data in China. The results show that the upper-level (200 hPa) ISO pattern for severe flood (drought) is characterized by an anticyclonic (cyclonic) circulation over the southern Tibetan Plateau and a cyclonic (anti-cyclonic) circulation over the northern Tibetan Plateau. The lower-level (850 hPa) ISO pattern is characterized by an anticyclonic (cyclonic) circulation over the area south of the Changjiang River, the South China Sea, and the Western Pacific, and a cyclonic (anticyclonic) circulation from the area north of the Changjiang River to Japan. These low-level ISO circulation patterns are the first modes of the ISO wind field according to the vector EOF expansion with stronger amplitude of the EOF1 time coefficient in severe flood years than in severe drought years. The analyses also reveal that at 500 hPa and 200 hPa, the atmospheric ISO activity over the Changjiang-Huaihe River basin, North China, and the middle-high latitudes north of China is stronger for severe flood than for severe drought. The ISO meridional wind over the middle-high latitude regions can propagate southwards and meet with the northward propagating ISO meridional wind from lower latitude regions over the Changjiang-Huaihe River Basin during severe flood years, but not during severe drought years.

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.

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

In terms of Kuo-Qian pesigma incorporated coordinate five-level primitive equation spheric band (70°N-30°S)model with the Ural high's effect introduced into it as initial and boundary conditions, study is made of the high's influence on Asian summer monsoon circulation and dryness / wetness of eastern China based on case contrast andcontrol experiments. Rusults show that as an excitation source, the blocking high produces a SE-NW stationarywavetrain with its upper-air atnicyclonic divergent circulation oust over a lower-level trough zone) precisely over themiddle to lower reaches of the Changjiang River, enhancing East Asian westerly jet, a situation that contributes toPerturbation growth, causing an additional secondary meridional circulation at the jet entrance, which intensifies theupdraft in the monsoon area. As such, the high's presence and its excited steady wavetrain represent the large-scalekey factors and acting mechanisms for the rainstorm over the Changjiang-Huaihe River catchment in the easternpart of the land.

Preyminary Investigations on the Global Summer Monsoonal Drought Mechanics and the Latitudinal Teleconnections

The question of possible teleconnections between the middle latitude general circulation and the Indian south-west monsoon was investigated in this paper. Within the framework of a simple model it was shown that there can exist such an interaction via the ultra-long Rossby waves.

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.

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.

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.

Transport of Water Vapor over North China during the Drought Period in Summer of 1980

The features of water vapor transport, such as temporal evolution, vertical structure and spatial pattern, over North China during the prolonged drought in the summer of 1980 have been analyzed through computation of water vapor flux based on the once daily ECMWF grid-point data at 12GMT. The results indicate that it is unlikely that the characteristics of the atmospheric mass divergence, ascending motion and stratification stability in North China were completely opposite to those in the Yangtze River Valley, where the heavy flood occurred in the summer of 1980. It is major differences that the strong ascending motion and significant water vapor convergence overlap fairly well each other in the vertical levels in the Yangtze River Valley, while the maximum ascending motion is accompanied by water vapor divergence or weak water vapor convergence in North China. This vertical structure in North China results in insufficient water vapor supply and, therefore, little condensation and precipitation in the middle and upper atmosphere were produced. Additionally, a mode of monthly-scale low frequency oscillation can be found in water vapor flux, which is in correspondence to the fluctuation period of rainfall.

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.

海温异常对长江流域夏季典型旱涝的影响研究

为研究长江流域夏季旱涝特征及其与海温异常之间的关联性,基于中国326个气象站降水量、NCEP/NCAR再分析资料等,采用合成分析、EOF分解等方法,分析了长江流域夏季典型旱涝年的降水分布、同期大气环流及前期海温特征,并以2018年为例,初步揭示了2018年前期海温异常对大气环流的可能影响。结果表明:①长江流域夏季典型旱年,仅嘉陵江和岷沱江会表现出局部偏涝,全国为典型的Ⅰ类雨型,多雨区位于黄河流域及以北地区。前期冬季赤道太平洋表现出类拉尼娜的东冷西暖分布,同时黑潮区海温偏低,西风漂流区海温偏暖。受多海域协同作用,同期欧亚环流场上自西北向东南呈现出“+-+”三极型分布,东亚地区为自北向南“-+-”的EAP负位相。长江流域典型涝年,全国多为典型的Ⅱ类和Ⅲ类雨型,环流及海温呈现出相反特征。②2018年为典型的长江中下游偏旱年,仅在岷沱江降水偏多近3成,为历史第4多,与长江流域夏季降水的主模态正位相类似,解释方差达24%。③2018年前冬出现弱拉尼娜、春末夏初西风漂流区异常偏暖、NAT异常正位相,三者共同作用,使得东亚副热带西风急流偏北,东亚沿岸出现EAP负位相,大陆热低压明显偏强,东亚夏季风为1961年以来最强,同时副高脊线最北,造成夏季降水主雨带北推至华北、西北地区,岷沱江、嘉陵江异常多,而长江中下游异常少,为典型的Ⅰ类雨型。研究成果可为长江流域旱涝预测、水资源调度提供参考。

2024年4-6月我国区域性高温干旱特征及其影响因子

在全球气候变暖的严峻形势下,区域性高温干旱事件愈发频繁,对生态环境、粮食安全、经济发展和生命健康构成重大威胁。2024年4—6月,我国华北、西北及西南地区再度遭遇高温干旱侵袭,农业生产遭受明显损失。本研究综合多种数据资料剖析上述3个区域高温干旱事件的演变特征及成因。结果表明,西南地区干旱主要发生在4月,而华北和西北地区自4月起旱情显现、5—6月旱情逐渐加剧(强度增强、范围扩大)。伴随旱情加剧,区域最高气温异常范围明显扩展,西北地区高温日数创历史新高,5月最高气温达到峰值,较旱情最为严重的6月提前一个月;西南和华北地区高温接近历史极值。进一步分析表明,华北地区干旱主要受太平洋地区环流调控,而高温则主要受低纬度太平洋环流及西太平洋暖池影响;西北地区的干旱主要与西太平洋副热带高压及北半球极涡密切相关,高温则主要来自北大西洋的影响;西南地区高温干旱的成因更为复杂,但主要聚焦于北半球副热带高压和低纬度太平洋、印度洋。从大气环流和水汽输送的角度审视,华北和西北旱情的主导因素为大陆高压的发展和维持,而西南地区的干旱则受偏北的西太平洋副热带高压引导,致使来自印度大陆的干热气流控制这一区域,造成水汽辐散,进而引发高温干旱灾害。

淮北平原不同时间尺度下的夏玉米干旱特征

【目的】在生长阶段和生长季内起始不定的10d尺度下,对淮北平原夏玉米的干旱时空特征进行研究,探索不同土层深度下的干旱规律,为夏季作物的抗旱灌溉提供更加科学合理的规划依据。【方法】基于干旱严重程度指数(DSI),将2010—2019年表土层(0~10cm)和根系主要分布层(0~50cm)的干旱状态进行分级,并利用M-K检验法和克里金空间插值法,在生长阶段和生长季内起始时间不定的10 d两种较小时间尺度下,对淮北平原夏玉米干旱的时间变化趋势和空间分布特征进行了分析。【结果】(1)自2016年生长季开始,砀山、蒙城、谯城站的干旱程度和频率显著升高,阜阳站干旱程度和频率都显著降低,而宿州站的干旱事件则集中在2010—2012、2019年生长季;与生长阶段尺度相比,部分干旱事件在生长季内起始不定的10 d尺度下的干旱程度更大,干旱频率也更高;(2)各个生长阶段的多年平均干旱指数最高的是播种—出苗期,达到了中旱以上,此生长阶段的干旱频率同时也最高,在40%以上;2种尺度下重旱以上的干旱事件常发生在北部砀山和中部蒙城、宿州区域;0~10 cm土层的干旱频率在西南部较高,0~50 cm土层的干旱频率则在东部和北部较高;(3)生长季内起始不定10 d尺度下,每个生长季干旱程度最高的时段其起始时间多数处于播种—出苗的早期,出苗—拔节的早期,拔节—抽雄的中期,且大都在重旱以上,少数发生在8月与9月。【结论】淮北平原夏玉米在2016年生长季之后有显著的干旱突变趋势,干旱程度和频率常常在播种—出苗期最高,相比于生长阶段时间尺度,在生长季内起始不定的10d尺度下会识别出更高的干旱程度,干旱频率也有所增大,同时能更确定严重干旱事件的发生时段。

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。