It is generally accepted that climate change is having a negative impact on food security. However, most of the literature variously focuses on the complex and many mechanisms linking climate stressors; the links with food production or productivity rather than food security; and future rather than current effects. In contrast, we investigate the extent to which current changes in food insecurity can be plausibly attributed to climate change. We combine food insecurity data for 83 countries from the FAO food insecurity experience scale (FIES) with reanalysed climate data from ERA5-Land, and use a panel data regression with time-varying coefficients. This framework allows us to estimate whether the relationship between food insecurity and temperature anomaly is changing over time. We also control for Human Development Index, and drought measured by six-month Standardized Precipitation Index. Our empirical findings suggest that for every 1 [Formula: see text] of temperature anomaly, severe global food insecurity has increased by 1.4% (95% CI 1.3-1.47) in 2014 but by 1.64% (95% CI 1.6-1.65) in 2019. This impact is higher in the case of moderate to severe food insecurity, with a 1 [Formula: see text] increase in temperature anomaly resulting in a 1.58% (95% CI 1.48-1.68) increase in 2014 but a 2.14% (95% CI 2.08-2.20) increase in 2019. Thus, the results show that the temperature anomaly has not only increased the probability of food insecurity, but the magnitude of this impact has increased over time. Our counterfactual analysis suggests that climate change has been responsible for reversing some of the improvements in food security that would otherwise have been realised, with the highest impact in Africa. Our analysis both provides more evidence of the costs of climate change, and as such the benefits of mitigation, and also highlights the importance of targeted and efficient policies to reduce food insecurity. These policies are likely to need to take into account local contexts, and might include efforts to increase crop yields, targeted safety nets, and behavioural programs to promote household resilience.© 2022. The Author(s).

Extreme weather and climate events, such as heat waves, cyclones, and floods, are an expression of climate variability. These events and events influenced by climate change, such as wildfires, continue to cause significant human morbidity and mortality and adversely affect mental health and well-being. Although adverse health impacts from extreme events declined over the past few decades, climate change and more people moving into harm's way could alter this trend. Long-term changes to Earth's energy balance are increasing the frequency and intensity of many extreme events and the probability of compound events, with trends projected to accelerate under certain greenhouse gas emissions scenarios. While most of these events cannot be completely avoided, many of the health risks could be prevented through building climate-resilient health systems with improved risk reduction, preparation, response, and recovery. Conducting vulnerability and adaptation assessments and developing health system adaptation plans can identify priority actions to effectively reduce risks, such as disaster risk management and more resilient infrastructure. The risks are urgent, so action is needed now.

Recent decades have been characterized by increasing temperatures worldwide, resulting in an exponential climb in vapor pressure deficit (VPD). VPD has been identified as an increasingly important driver of plant functioning in terrestrial biomes and has been established as a major contributor in recent drought-induced plant mortality independent of other drivers associated with climate change. Despite this, few studies have isolated the physiological response of plant functioning to high VPD, thus limiting our understanding and ability to predict future impacts on terrestrial ecosystems. An abundance of evidence suggests that stomatal conductance declines under high VPD and transpiration increases in most species up until a given VPD threshold, leading to a cascade of subsequent impacts including reduced photosynthesis and growth, and higher risks of carbon starvation and hydraulic failure. Incorporation of photosynthetic and hydraulic traits in 'next-generation' land-surface models has the greatest potential for improved prediction of VPD responses at the plant- and global-scale, and will yield more mechanistic simulations of plant responses to a changing climate. By providing a fully integrated framework and evaluation of the impacts of high VPD on plant function, improvements in forecasting and long-term projections of climate impacts can be made.© 2020 The Authors. New Phytologist © 2020 New Phytologist Trust.

Rising air temperatures are a leading risk to global crop production. Recent research has emphasized the critical role of moisture availability in regulating crop responses to heat and the importance of temperature-moisture couplings in driving concurrent heat and drought. Here, we demonstrate that the heat sensitivity of key global crops depends on the local strength of couplings between temperature and moisture in the climate system. Over 1970-2013, maize and soy yields dropped more during hotter growing seasons in places where decreased precipitation and evapotranspiration more strongly accompanied higher temperatures, suggestive of compound heat-drought impacts on crops. On the basis of this historical pattern and a suite of climate model projections, we show that changes in temperature-moisture couplings in response to warming could enhance the heat sensitivity of these crops as temperatures rise, worsening the impact of warming by -5% (-17 to 11% across climate models) on global average. However, these changes will benefit crops where couplings weaken, including much of Asia, and projected impacts are highly uncertain in some regions. Our results demonstrate that climate change will impact crops not only through warming but also through changing drivers of compound heat-moisture stresses, which may alter the sensitivity of crop yields to heat as warming proceeds. Robust adaptation of cropping systems will need to consider this underappreciated risk to food production from climate change.© 2021. The Author(s), under exclusive licence to Springer Nature Limited.

Climate extremes have profound impacts on key socio-economic sectors such as agriculture. In a changing climate context, characterised by an intensification of these extremes and where the population is expected to grow, exposure and vulnerability must be accurately assessed. However, most risk assessments analyse extremes independently, thus potentially being overconfident in the resilience of the socio-economic sectors. Here, we propose a novel approach to defining and characterising concurrent climate extremes (i.e. extremes occurring within a specific temporal lag), which is able to identify spatio-temporal dependences without making any strict assumptions. The method is applied to large-scale heat stress and drought events in the key wheat producing regions of the world, as these extremes can cause serious yield losses and thus trigger market shocks. Wheat regions likely to have concurrent extremes (heat stress and drought events) are identified, as well as regions independent of each other or inhibiting each other in terms of these extreme events. This tool may be integrated in all risk assessments but could also be used to explore global climate teleconnections.

Climate extremes cause significant winter wheat yield loss and can cause much greater impacts than single extremes in isolation when multiple extremes occur simultaneously. Here we show that compound hot-dry-windy events (HDW) significantly increased in the U.S. Great Plains from 1982 to 2020. These HDW events were the most impactful drivers for wheat yield loss, accounting for a 4% yield reduction per 10 h of HDW during heading to maturity. Current HDW trends are associated with yield reduction rates of up to 0.09 t ha per decade and HDW variations are atmospheric-bridged with the Pacific Decadal Oscillation. We quantify the "yield shock", which is spatially distributed, with the losses in severely HDW-affected areas, presumably the same areas affected by the Dust Bowl of the 1930s. Our findings indicate that compound HDW, which traditional risk assessments overlooked, have significant implications for the U.S. winter wheat production and beyond.© 2022. The Author(s).

Compound events of climate extremes such as extremely high temperature and low precipitation during crop growing seasons can greatly affect agricultural production and food security. No study has investigated how Compound Extreme Hot and Dry days (CEHD days) during crop-growing seasons have changed or will change in response to climate warming. Based on observations, we find upward trends in CEHD days during wheat and maize growing seasons in China in the historical period 1980-2015. These trends are remarkably different during wheat and maize growing seasons, pointing to the need for targeted analysis focusing on crop-specific growing seasons. Projections of future temperature and precipitation from the Coordinated Regional Climate Downscaling Experiment show that upward trends will continue into future. On average over China, the frequencies of CEHD days during wheat and maize growing seasons are projected to increase respectively by 168% and 162% in 2036-2050 relatively to 1980-2015 under the RCP8.5 emissions scenario. The projected increases may have serious implications for China's food production, adding to the need for resilience planning to limit the impacts of growing-season CEHD days.

Compound events (CEs) are weather and climate events that result from multiple hazards or drivers with the potential to cause severe socio-economic impacts. Compared with isolated hazards, the multiple hazards/drivers associated with CEs can lead to higher economic losses and death tolls. Here, we provide the first analysis of multiple multivariate CEs potentially causing high-impact floods, droughts, and fires. Using observations and reanalysis data during 1980-2014, we analyse 27 hazard pairs and provide the first spatial estimates of their occurrences on the global scale. We identify hotspots of multivariate CEs including many socio-economically important regions such as North America, Russia and western Europe. We analyse the relative importance of different multivariate CEs in six continental regions to highlight CEs posing the highest risk. Our results provide initial guidance to assess the regional risk of CE events and an observationally-based dataset to aid evaluation of climate models for simulating multivariate CEs.

Drought and high temperature often occurs simultaneously, causing significant yield losses in wheat (Triticum aestivum L.). The objectives of this study were to: (i) quantify independent and combined effects of drought and high temperature stress on synthetic hexaploid wheat genotypes at anthesis and at 21 days after anthesis; and (ii) determine whether responses to stress varied among genotypes. Four synthetic hexaploid and two spring wheat genotypes were grown from emergence to anthesis (Experiment I) and emergence to 21 days after anthesis (Experiment II), with full irrigation and 21/15°C day/night temperature. Thereafter, four treatments were imposed for 16 days as (a) optimum condition: irrigation+21/15°C, (b) drought stress: withhold irrigation+21/15°C, (c) high temperature stress: irrigation+36/30°C and (d) combined stress: withhold irrigation+36/30°C. Results indicated a decrease in leaf chlorophyll, individual grain weight and grain yield in an increasing magnitude of drought<high temperature<combined stress. There were 69, 81 and 92% grain yield decreases in Experiment I and 26, 37 and 50% in Experiment II under drought, high temperature and combined stress respectively. Synthetic hexaploid wheat genotypes varied in their response to stresses. Genotypes ALTAR 84/AO'S' and ALTAR 84/Aegilops tauschii Coss. (WX 193) were least affected by combined stress in Experiments I and II respectively. Overall, combined effect of drought+high temperature stress was more detrimental than the individual stress and the interaction effect was hypo-additive in nature.

Environmental stress conditions such as drought, heat, salinity, cold, or pathogen infection can have a devastating impact on plant growth and yield under field conditions. Nevertheless, the effects of these stresses on plants are typically being studied under controlled growth conditions in the laboratory. The field environment is very different from the controlled conditions used in laboratory studies, and often involves the simultaneous exposure of plants to more than one abiotic and/or biotic stress condition, such as a combination of drought and heat, drought and cold, salinity and heat, or any of the major abiotic stresses combined with pathogen infection. Recent studies have revealed that the response of plants to combinations of two or more stress conditions is unique and cannot be directly extrapolated from the response of plants to each of the different stresses applied individually. Moreover, the simultaneous occurrence of different stresses results in a high degree of complexity in plant responses, as the responses to the combined stresses are largely controlled by different, and sometimes opposing, signaling pathways that may interact and inhibit each other. In this review, we will provide an update on recent studies focusing on the response of plants to a combination of different stresses. In particular, we will address how different stress responses are integrated and how they impact plant growth and physiological traits.© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.

Although extreme weather events recur periodically everywhere, the impacts of their simultaneous occurrence on crop yields are globally unknown. In this study, we estimate the impacts of combined hot and dry extremes as well as cold and wet extremes on maize, rice, soybean, and wheat yields using gridded weather data and reported crop yield data at the global scale for 1980-2009. Our results show that co-occurring extremely hot and dry events have globally consistent negative effects on the yields of all inspected crop types. Extremely cold and wet conditions were observed to reduce crop yields globally too, although to a lesser extent and the impacts being more uncertain and inconsistent. Critically, we found that over the study period, the probability of co-occurring extreme hot and dry events during the growing season increased across all inspected crop types; wheat showing the largest, up to a six-fold, increase. Hence, our study highlights the potentially detrimental impacts that increasing climate variability can have on global food production.© 2023. The Author(s).

There is high confidence that climate change has increased the probability of concurrent temperature-precipitation extremes, changed their spatial-temporal variations and affected the relationships between drivers of such natural hazards. However, the extent of such changes has been less investigated in Australia. We used 131 years (1889-2019) of daily data from SILO gridded data set at 700 grid cells (1 degrees x 1 degrees) across Australia to calculate annual and seasonal mean daily maximum temperature (MMT) and total precipitation (TPR). A nonparametric multivariate copula framework was adopted to estimate the return period of compound hot-dry (CHD) events based on an 'And' hazard scenario (hotter than a threshold 'And' drier than a threshold). We defined CHD extremes as years with joint return periods of longer than 25 years calculated over the period 1889-2019. Mann-Kendall nonparametric tests were used to analyse trends in MMT and TPR as well as in the frequency of univariate and CHD extremes. We found a general cooling-wetting trend over 1889-1989. Significant increasing trends were detected over 1990-2019 in the frequency and severity of hot extremes across the country while trends in dry extremes were mostly insignificant (and decreasing). We showed a significant increase in the association between temperature and precipitation at various temporal scales. The frequency of CHD extremes was mostly stable over 1889-1989, but significantly increased between 1990 and 2019 at 44% of studied grid cells, mostly located in the north, south-east and southwest.

Irrigation is the largest sector of human water use and an important option for increasing crop production and reducing drought impacts. However, the potential for irrigation to contribute to global crop yields remains uncertain. Here, we quantify this contribution for wheat and maize at global scale by developing a Bayesian framework integrating empirical estimates and gridded global crop models on new maps of the relative difference between attainable rainfed and irrigated yield (ΔY). At global scale, ΔY is 34 ± 9% for wheat and 22 ± 13% for maize, with large spatial differences driven more by patterns of precipitation than that of evaporative demand. Comparing irrigation demands with renewable water supply, we find 30-47% of contemporary rainfed agriculture of wheat and maize cannot achieve yield gap closure utilizing current river discharge, unless more water diversion projects are set in place, putting into question the potential of irrigation to mitigate climate change impacts.

Irrigation has been pivotal in wheat's rise as a major crop in India and is likely to be increasingly important as an adaptation response to climate change. Here we use historical data across 40 years to quantify the contribution of irrigation to wheat yield increases and the extent to which irrigation reduces sensitivity to heat. We estimate that national yields in the 2000s are 13% higher than they would have been without irrigation trends since 1970. Moreover, irrigated wheat exhibits roughly one-quarter of the heat sensitivity estimated for fully rainfed conditions. However, yield gains from irrigation expansion have slowed in recent years and negative impacts of warming have continued to accrue despite lower heat sensitivity from the widespread expansion of irrigation. We conclude that as constraints on expanding irrigation become more binding, furthering yield gains in the face of additional warming is likely to present an increasingly difficult challenge.

【目的】在黄淮北片气象灾害频发的异常气候背景下，通过筛选抗旱、耐热和抗寒的冬小麦品种，明确抗逆广适品种的产量构成特征、株型结构特征和生理特征，为抗逆广适品种筛选工作提供简易检测指标。【方法】于2017年秋至2020年夏连续3个小麦生长季在河北藁城堤上试验站进行大田水分试验（试验1）和温室试验（试验2），同时，利用2018年和2020年春季自然低温进行抗寒品种筛选试验；试验1设置3个灌水处理，0水、1水（拔节水）和2水（拔节水+开花水），试验2设置2个温度处理，灌浆后期常温对照和增温处理，以16个冬小麦品种为材料，测定抗逆性能评价指标、产量形成指标、株型结构指标和叶片生理指标。【结果】综合考虑产量、抗旱指数、产量热感指数和冻害级别，筛选出济麦23、山农30、冀麦325、济麦22、品育8012 5个冬小麦品种，这些品种综合表现较优，具有抗旱、耐热、抗寒性强、丰产稳产的特点。通过分析产量与产量形成指标、株型指标和叶片生理指标的相关性，千粒重、收获指数和生物产量与产量呈极显著正相关；旗叶叶宽、茎粗和穗长与产量呈显著或极显著正相关，而旗叶茎叶夹角与产量呈显著负相关；旗叶相对叶绿素值（SPAD值）和相对含水量与产量均呈极显著正相关，冠层温度与产量呈极显著负相关。与其他品种比较，抗逆广适品种千粒重、收获指数和生物产量分别提高了12.9%、5.2%和3.4%；旗叶叶宽为（16.2±0.4） cm、茎叶夹角（18.2±3.2）°、基部茎粗（4.0±0.3） mm、穗长（7.5±0.14） cm、株高（80.3±1.3） cm；灌浆后期旗叶SPAD值和相对含水量分别提高了9.8%和4.2%、冠层温度降低了1.9 ℃。【结论】明确了抗逆广适小麦品种“上部紧凑直立、下部松散平展”的优化株型，提出了旗叶叶宽、茎叶夹角、基部茎粗、穗长的定量指标；明确了生育后期旗叶SPAD和相对含水量较高、冠层温度较低的生理特征以及千粒重、收获指数和生物产量较高的产量特征。

【目的】 本研究基于气候室模拟温度日变化特征,旨在探讨氮素对高温、干旱及复合胁迫下冬小麦地上干物质重、氮积累与分配、氮代谢相关酶活性、蛋白质含量、产量及水氮利用效率的影响。【方法】 基于人工气候室开展冬小麦盆栽试验,以小偃22号为试验材料,采用裂-裂区随机完全区组设计,以2个温度处理（高温：H;适宜温度：S）为主区,以2个水分水平（干旱：D;充分供水：F）为裂区,3个施氮水平（低氮：N₁;中氮：N₂;高氮：N₃）为裂-裂区,研究冬小麦生长生理特性、产量及水氮利用效率对高温干旱胁迫及各施氮量的响应特征。【结果】 高温、干旱及复合胁迫导致地上总干物质重（ADW）和氮积累量（ANA）降低。在成熟期,高温干旱复合胁迫（HD）和干旱胁迫（SD）下N₃处理ANA分别较N₁处理增加7.26%和6.82%。高温、干旱及复合胁迫提高小麦花前氮素对籽粒贡献率（NRR）,HD胁迫各施氮处理NRR均值较对照（SF）增加达38.21%,施氮量的增加扩大这种增加效应。高温、干旱及复合胁迫导致成熟期穗氮分配率降低,特别是复合胁迫。暴露于高温、干旱及复合胁迫下籽粒蛋白质产量（PY）降低,干旱胁迫（7.37%）各施氮处理PY均值较高温胁迫（3.94%）降低更多,无论单一或复合胁迫下籽粒PY均在N₂处理下显著增加。此外,单一的干旱和高温胁迫下降低的谷氨酰胺合成酶（GS）和硝酸还原酶（NR）活性在N₂处理下显著增加,复合胁迫N₁处理NR和GS活性分别较N₃处理提高23.81%和23.07%。与对照相比,干旱胁迫各施氮处理穗粒数、千粒重和产量均值的降幅均高于高温胁迫,N₂处理对高温和干旱胁迫下这些参数存在明显正向调控,产量水分利用效率（WUE_g）和生物量水分利用效率（WUE_b）在N₂处理下得到明显改善。充分供水+N₂处理籽粒（NUE_g）分别较低干旱和复合胁迫N₃处理提高19.09%和19.44%,表明在水分充足条件下中氮能有效地缓解干旱和高温胁迫下籽粒氮利用效率的降低。NUE_g和NUE_b的提高可能归因于合理氮肥调控下增加的GS和NR活性。主成分分析表明胁迫条件下小麦千粒重和ADW与产量的关系更紧密。【结论】 高温和干旱胁迫的综合效应比单一胁迫对小麦危害更大。在单一高温和干旱胁迫下,适量增加氮输入能增加氮代谢酶活性并维持更高氮代谢能力,提高籽粒氮积累量及蛋白质产量,将更有利于提高产量及水氮利用效率。然而在花后遭遇高温干旱复合胁迫时,相比低施氮量,增加施氮对小麦产量形成及水氮的吸收利用均产生一定抑制作用,应适当减少氮肥用量。

【Objective】 The diurnal variation of temperature was simulated based on the growth chamber, this study aimed to investigate the effects of nitrogen (N) on dry matter accumulation, N accumulation and distribution, activities of N metabolism-related enzymes, protein content, yield, and water and N use efficiency of winter wheat plants under heat, drought and combined stress.【Method】 The experiments were carried out based on growth chambers with Xiaoyan 22 as test material. The experiment consisted of three blocks, in which two temperature treatments (high temperature: H; suitable temperature: S) were assigned as the main plot, two watering treatments (drought: D; sufficient water supply: F) were arranged split-plot, and three N supply levels (low N: N1; medium N: N2; high N: N3) were arranged split-split plot to form a completely randomized block design to investigate the response of the growth and physiological characteristics, yield, and water and N use efficiency in wheat plants to heat, drought stress and different N applications.【Result】 Heat, drought and combined stress resulted in the decrease in ADW (aboveground dry weight) and ANA (aboveground nitrogen accumulation). At maturity, the ANA of N3 supply under HD and SD was higher 7.26% and 6.82% than that under N1 supply, respectively. Heat, drought and combined stress resulted in the increase in NRR, and the average NRR of three N supplies under HD increased by 38.21% compared with the control, while increasing N supply further expanded this increasing effect. Heat, drought and combined stress led to decrease in N distribution rate of panicle at maturity, especially combined stress. PY decreased significantly when exposed to heat, drought and combined stress. Compared with the control, the decrease of PY under drought stress conditions (7.37%) was more obvious than that under heat stress conditions (3.94%). Under individual and combined stress treatments, PY was significantly increased under N2 supply. Furthermore, GS and NR activities decreased under individual heat and drought stress, which were significantly increased under regulation of N2 supply. The NR and GS activities of N1 supply under HD were 23.81% and 23.07% higher than that of N3 supply, respectively. Compared with the control, the reduction in grain number per spike, 1000 grain weight and yield under drought stress conditions was greater than that under heat stress. N2 supply had an obvious positive effect on these parameters of the two stress treatments, and WUEg and WUEb were significantly improved under N2 supply. Adequate water supply under N2 had 19.09% and 19.44% higher NUEg than drought and combined stress under N3, respectively. This indicates adequate water supply under medium N could effectively alleviate the decrease of NUEg induced by drought and heat stress. The increase of NUEg and NUEb might be attributed to increase of GS and NR activities by appropriate N supply. Principal component analysis indicated that TGW and ADW of wheat were more closely related to yield under stresses conditions.【Conclusion】 The results showed that combined effect of drought and heat stress was more detrimental than individual stresses. Under individual heat and drought stress, an appropriate N supply could increase the activities of N metabolism enzymes and maintain higher N metabolism capacity, improve GNA and PY, and would be much more beneficial to increasing grain yield, water and N use efficiency in wheat production. However, when wheat was subjected to the combined stress after anthesis, compared with low N supply, increasing N supply had a restrictive effect on wheat yield formation as well as water and N utilization capacity, while N supply should be appropriately reduced.

Farmers and breeders have long known that often it is the simultaneous occurrence of several abiotic stresses, rather than a particular stress condition, that is most lethal to crops. Surprisingly, the co-occurrence of different stresses is rarely addressed by molecular biologists that study plant acclimation. Recent studies have revealed that the response of plants to a combination of two different abiotic stresses is unique and cannot be directly extrapolated from the response of plants to each of the different stresses applied individually. Tolerance to a combination of different stress conditions, particularly those that mimic the field environment, should be the focus of future research programs aimed at developing transgenic crops and plants with enhanced tolerance to naturally occurring environmental conditions.

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop-level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well-adapted crops with similar phenology: bread wheat and two-row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose-built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post-flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C(-1) ), due to GN reductions (ca. 6% °C(-1) ) linked to a lower number of spikes per m(2). An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.© 2015 John Wiley & Sons Ltd.