1961-2010年潜在干旱对我国夏玉米产量影响的模拟分析

玉米是我国重要的粮食和饲料作物,旱灾是玉米生产中常见的气象灾害。采用CERES-Maize作物模拟模型,模拟了1961—2010年潜在干旱对我国夏玉米产量影响的时空变化趋势,并分析了其与大气环流因子间的关系,以期了解我国50年来夏玉米受旱的变化情况,并为干旱的研究方法提供一些参考。结果表明:(1)1961—2010年我国夏玉米的潜在产量损失呈略微下降的趋势,不同时期表现不同,其中20世纪60年代、90年代表现为上升趋势。(2)在过去50年里,我国夏玉米潜在旱灾损失中心有向东北移动的趋势,华北地区受旱程度的减轻和东北地区受旱程度的增强是造成损失中心移动的主要原因。(3)我国夏玉米潜在旱灾产量损失中心的经纬度和影响我国夏季降水的北极涡、副热带高压系统的部分指数具有显著的相关关系。当北极涡在生长季前期或同期偏小、偏弱时,我国夏玉米潜在旱灾产量损失中心将偏东、偏北,而副热带高压系统影响更为复杂。     

昆虫对降雨和干旱的响应与适应

水分因子在昆虫的生长发育及其整个生活史中起着至关重要的作用。降雨作为改变环境水分的方式之一,其机械冲刷作用对昆虫具有直接的致死效应,并影响昆虫的生长发育、繁殖及其产卵和取食行为等;干旱作为降雨减少导致的极端环境形式,不仅对昆虫生理产生直接影响,而且还会通过影响寄主植物而间接作用于昆虫;同时,干旱还会改变同一寄主植物上昆虫之间的种间关系,导致群落多样性和稳定性的变化以及种群演替的发生。本文综述了气候变化背景下降雨和干旱对昆虫生长发育和繁殖的影响,并介绍了迁飞型昆虫、群居型昆虫、土壤害虫等对降雨和干旱的行为反应;此外,还详细介绍了昆虫对降雨和干旱的适应对策(包括对水分因子的行为适应对策、滞育和迁飞对策等),并建议利用环境水分(尤其是土壤水分)调控措施(如人工降雨和灌溉等)来防治农业害虫。     

A review of the relationships between drought and forest fire in the United States

The historical and presettlement relationships between drought and wildfire are well documented in North America, with forest fire occurrence and area clearly increasing in response to drought. There is also evidence that drought interacts with other controls (forest productivity, topography, fire weather, management activities) to affect fire intensity, severity, extent, and frequency. Fire regime characteristics arise across many individual fires at a variety of spatial and temporal scales, so both weather and climate – including short‐ and long‐term droughts – are important and influence several, but not all, aspects of fire regimes. We review relationships between drought and fire regimes in United States forests, fire‐related drought metrics and expected changes in fire risk, and implications for fire management under climate change. Collectively, this points to a conceptual model of fire on real landscapes: fire regimes, and how they change through time, are products of fuels and how other factors affect their availability (abundance, arrangement, continuity) and flammability (moisture, chemical composition). Climate, management, and land use all affect availability, flammability, and probability of ignition differently in different parts of North America. From a fire ecology perspective, the concept of drought varies with scale, application, scientific or management objective, and ecosystem.     

干旱胁迫对不同耐旱性玉米杂交种产量和根系生理特性的影响

通过盆栽人工模拟干旱试验,研究了全生育期中度干旱胁迫对不同耐旱性玉米杂交种（耐旱：京科628;不耐旱：农大95）产量及根系生理特性的影响.结果表明：干旱胁迫下,耐旱玉米产量比对照减少33.7%,不耐旱玉米则比对照减少62.3%.干旱胁迫下,玉米根系生物量降低且最大值出现时间提前,与对照相比,不耐旱玉米根冠比升高,耐旱玉米根冠比前期升高后期降低;根系活力降低,不耐旱玉米根系活力降低幅度大于耐旱玉米;根系超氧化物歧化酶（SOD）活性前期高于对照后期低于对照,耐旱玉米根系SOD活性开始低于对照的时间比不耐旱玉米晚;根系丙二醛（MDA）含量升高,随干旱胁迫处理时间的延长,不耐旱玉米MDA含量比对照升高的幅度大于耐旱玉米;根系可溶性蛋白含量降低,不耐旱玉米的降低幅度大于耐旱玉米.干旱胁迫下耐旱玉米杂交种根系活力﹑根系SOD活性及可溶性蛋白含量较高,减缓了根系的衰老进程,延长了根系功能期,这可能是耐旱玉米杂交种在干旱胁迫下仍能获得较高产量的重要原因之一.     

A multi-satellite framework to rapidly evaluate extreme biosphere cascades: The Western US 2021 drought and heatwave

The increasing frequency and intensity of climate extremes and complex ecosystem responses motivate the need for integrated observational studies at low latency to determine biosphere responses and carbon-climate feedbacks. Here, we develop a satellite-based rapid attribution workflow and demonstrate its use at a 1–2-month latency to attribute drivers of the carbon cycle feedbacks during the 2020–2021 Western US drought and heatwave. In the first half of 2021, concurrent negative photosynthesis anomalies and large positive column CO₂ anomalies were detected with satellites. Using a simple atmospheric mass balance approach, we estimate a surface carbon efflux anomaly of 132 TgC in June 2021, a magnitude corroborated independently with a dynamic global vegetation model. Integrated satellite observations of hydrologic processes, representing the soil–plant–atmosphere continuum (SPAC), show that these surface carbon flux anomalies are largely due to substantial reductions in photosynthesis because of a spatially widespread moisture-deficit propagation through the SPAC between 2020 and 2021. A causal model indicates deep soil moisture stores partially drove photosynthesis, maintaining its values in 2020 and driving its declines throughout 2021. The causal model also suggests legacy effects may have amplified photosynthesis deficits in 2021 beyond the direct effects of environmental forcing. The integrated, observation framework presented here provides a valuable first assessment of a biosphere extreme response and an independent testbed for improving drought propagation and mechanisms in models. The rapid identification of extreme carbon anomalies and hotspots can also aid mitigation and adaptation decisions.     

荒漠短命植物地上和地下生产力对极端干旱和降水的响应

在古尔班通古特沙漠南缘沙垄4个坡位和坡向,设置减少65%和增加65%生长季降水量以模拟极端干旱和极端降水事件,研究极端干旱和极端降水事件对沙垄不同坡位和坡向短命植物层片生产力的影响。结果表明: 极端干旱使地上净初级生产力和地下净初级生产力分别显著降低48.8%和13.7%,极端降水使地上净初级生产力和地下净初级生产力分别显著增加37.9%和23.2%。地上净初级生产力对极端干旱和极端降水的敏感性(0.26和0.21 g·m^-2·mm^-1)显著强于地下净初级生产力的敏感性(0.02和0.03 g·m^-2·mm^-1)。沙垄东坡地上净初级生产力(24.22 g·m^-2)和地下净初级生产力(5.77 g·m^-2)与西坡相比显著增大29.7%和71.7%,而地上净初级生产力和地下净初级生产力对降水变化的敏感性在不同坡位和坡向之间差异不显著。     

基于SPEI的辽宁省玉米生育期干旱特征分析

在全球气候变暖的背景下,探究玉米生育期的气候变化及干旱特征,对于预防干旱灾害对作物造成的损失,以及农业可持续发展意义重大。基于1967—2018年辽宁省33个国家级气象台站逐日观测数据,计算了不同月尺度下玉米各生育期标准降水蒸散指数（SPEI）,并结合干旱频率及干旱站次比综合分析了干旱时空变化情况。结果表明：（1）辽宁省玉米生育期降水量以13.31 mm/10a的速率减少,与SPEI呈显著正相关（P<0.01）;气温以0.25℃/10a的速率显著上升（P<0.01）,与SPEI呈负相关。（2）播种-出苗期、出苗-拔节期和喇叭口期SPEI在时间上均呈上升趋势,抽雄期和成熟期呈降低趋势;在空间上全生育期SPEI表现为西北向东南递增趋势。（3）全生育期干旱站次比以0.41%/10a的速率上升;出苗-拔节期干旱站次比呈减少趋势,其他生育阶段均呈上升趋势;发生干旱类型频次区域性干旱 > 部分区域性干旱 > 局域性干旱 > 全域性干旱。（4）全生育期干旱频率整体呈现出由西北向东南递减的特征,且干旱频发区主要在辽西地区;干旱发生频率轻旱 > 中旱 > 重旱 > 特旱。（5）出苗-拔节期为干旱站次比最高的时期;SPEI平均值和不同等级干旱频率最高的时期均为播种-出苗期。该研究成果可为区域农业干旱风险评价以及抗灾减灾等提供参考。     

The impacts of increasing drought on forest dynamics,structure, and biodiversity in the United States

We synthesize insights from current understanding of drought impacts at stand‐to‐biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand‐level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. In the eastern US, the effects of increasing drought are becoming better understood at the level of individual trees, but this knowledge cannot yet be confidently translated to predictions of changing structure and diversity of forest stands. While eastern forests have not experienced the types of changes seen in western forests in recent decades, they too are vulnerable to drought and could experience significant changes with increased severity, frequency, or duration in drought. Throughout the continental United States, the combination of projected large climate‐induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought‐tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.     

Recent cover crop adoption is associated with small maize and soybean yield losses in the United States

Cover crops are gaining traction in many agricultural regions, partly driven by increased public subsidies and by private markets for ecosystem services. These payments are motivated by environmental benefits, including improved soil health, reduced erosion, and increased soil organic carbon. However, previous work based on experimental plots or crop modeling indicates cover crops may reduce crop yields. It remains unclear, though, how recent cover crop adoption has affected productivity in commercial agricultural systems. Here we perform the first large-scale, field-level analysis of observed yield impacts from cover cropping as implemented across the US Corn Belt. We use validated satellite data products at sub-field scales to analyze maize and soybean yield outcomes for over 90,000 fields in 2019–2020. Because we lack data on cover crop species or timing, we seek to quantify the yield impacts of cover cropping as currently practiced in aggregate. Using causal forests analysis, we estimate an average maize yield loss of 5.5% on fields where cover crops were used for 3 or more years, compared with fields that did not adopt cover cropping. Maize yield losses were larger on fields with better soil ratings, cooler mid-season temperatures, and lower spring rainfall. For soybeans, average yield losses were 3.5%, with larger impacts on fields with warmer June temperatures, lower spring and late-season rainfall, and, to a lesser extent, better soils. Estimated impacts are consistent with multiple mechanisms indicated by experimental and simulation-based studies, including the effects of cover crops on nitrogen dynamics, water consumption, and soil oxygen depletion. Our results suggest a need to improve cover crop management to reduce yield penalties, and a potential need to target subsidies based on likely yield impacts. Ultimately, avoiding substantial yield penalties is important for realizing widespread adoption and associated benefits for water quality, erosion, soil carbon, and greenhouse gas emissions.     

Phenological responses to extreme droughts in a Mediterranean forest

Mediterranean regions are projected to experience more frequent, prolonged and severe drought as a consequence of climate change. We used a retractable rainfall shelter, to investigate the impact of extreme droughts on the development of Quercus ilex leaves, flowers and fruit. In 2008, 97% of rainfall was excluded from a forest plot during the autumn, representing 50% of the 1127 mm of rain that fell during the year. In 2009, 87% of rainfall was excluded during the spring, representing 58% of the 749 mm that fell during the year. The rainfall shelter did not impact neither incident radiation nor air temperature. Autumn rainfall exclusion did not significantly affect leaf, flowers or fruit development. Spring rainfall exclusion resulted in larger and more sustained depression of leaf water potential during the key phases of foliar and floral development. Consequently, only half of the sampled trees (6) reached the shoot lengthening stage which leads to functionally mature leaves (phenophase 4), with one abandoning leaf development at budburst (phenophase 3) and the other two at the bud swelling stage (phenophase 2). All trees of the control plot passed phenophase 4, with most reaching complete leaf development. The impact of extreme droughts on flower development differed between the sexes. The spring exclusion had no effect on male flower, but only one of six trees completed female fruit maturation, compared with four in the control plot. The difference between the male and female drought impacts is likely attributable to the occurrence of male floral development before the period of lowest leaf water potential, and to the lower resource allocation requirements of male flowers. The information provided by our experimental approach may constitute a crucial step to evaluate the impact of increasing drought due to climate change on the most dominant Mediterranean tree species and to help drawing a full picture of the ecological consequences of the decline in water resource on forest dynamics under changing conditions.     

不同生育期持续干旱对玉米的影响及其与减产率的定量关系

为了探究不同生长阶段土壤水分含量持续下降过程对玉米生长发育和产量形成的影响,通过设置遮雨棚人工控水试验,分析不同生长阶段持续干旱条件下玉米株高、叶面积指数(LAI)、光合性能、地上生物量和产量等生理生态指标的动态变化.试验因素为控水时段和控水持续时间,从拔节普遍期开始分别控水20(T₁)和27 d(T₂),从抽雄普遍期开始控水20(T₃)和27 d(T₄),加上不控水对照(CK),共5个处理.结果表明: 持续干旱导致植株叶片卷曲、打绺,下部叶片衰老加快,对LAI影响较大,从而降低生物量的累积与籽粒产量.T₁～T₄处理结束时LAI分别为CK的74.9%、68.2%、60.5%和48.3%.玉米植株在经历持续控水后,叶片最大净光合速率(P_{n max})逐渐下降,T₁(T₃)和T₂(T₄)处理结束时P_{n max}分别降至CK的23%及不足10%,复水2周后,P_{n max}能恢复到CK的90%左右.T₁和T₂处理产量较CK分别下降18.5%和24.0%,T₃和T₄处理分别减产41.6%和45.8%.抽雄期持续干旱对玉米地上生物量及产量构成的影响大于拔节期干旱.干旱程度(D)能够定量表示土壤干旱状况,与玉米减产率存在线性定量关系,可通过计算D来预测玉米的减产情况.     

Near‐future forest vulnerability to drought and fire varies across the western United States

Recent prolonged droughts and catastrophic wildfires in the western United States have raised concerns about the potential for forest mortality to impact forest structure, forest ecosystem services, and the economic vitality of communities in the coming decades. We used the Community Land Model (CLM) to determine forest vulnerability to mortality from drought and fire by the year 2049. We modified CLM to represent 13 major forest types in the western United States and ran simulations at a 4‐km grid resolution, driven with climate projections from two general circulation models under one emissions scenario (RCP 8.5). We developed metrics of vulnerability to short‐term extreme and prolonged drought based on annual allocation to stem growth and net primary productivity. We calculated fire vulnerability based on changes in simulated future area burned relative to historical area burned. Simulated historical drought vulnerability was medium to high in areas with observations of recent drought‐related mortality. Comparisons of observed and simulated historical area burned indicate simulated future fire vulnerability could be underestimated by 3% in the Sierra Nevada and overestimated by 3% in the Rocky Mountains. Projections show that water‐limited forests in the Rocky Mountains, Southwest, and Great Basin regions will be the most vulnerable to future drought‐related mortality, and vulnerability to future fire will be highest in the Sierra Nevada and portions of the Rocky Mountains. High carbon‐density forests in the Pacific coast and western Cascades regions are projected to be the least vulnerable to either drought or fire. Importantly, differences in climate projections lead to only 1% of the domain with conflicting low and high vulnerability to fire and no area with conflicting drought vulnerability. Our drought vulnerability metrics could be incorporated as probabilistic mortality rates in earth system models, enabling more robust estimates of the feedbacks between the land and atmosphere over the 21st century.     

Crop yield response to climate change varies with cropping intensity

Projections of the response of crop yield to climate change at different spatial scales are known to vary. However, understanding of the causes of systematic differences across scale is limited. Here, we hypothesize that heterogeneous cropping intensity is one source of scale dependency. Analysis of observed global data and regional crop modelling demonstrate that areas of high vs. low cropping intensity can have systematically different yields, in both observations and simulations. Analysis of global crop data suggests that heterogeneity in cropping intensity is a likely source of scale dependency for a number of crops across the globe. Further crop modelling and a meta‐analysis of projected tropical maize yields are used to assess the implications for climate change assessments. The results show that scale dependency is a potential source of systematic bias. We conclude that spatially comprehensive assessments of climate impacts based on yield alone, without accounting for cropping intensity, are prone to systematic overestimation of climate impacts. The findings therefore suggest a need for greater attention to crop suitability and land use change when assessing the impacts of climate change.     

干旱对东北春玉米生长发育和产量的影响

选取玉米品种丹玉39为供试材料,利用大型农田水分控制试验场,采用大田池栽方式,在玉米三叶-拔节期、拔节-吐丝期、吐丝-乳熟期分别开展中度干旱胁迫及复水控制对比试验,分析3个关键生育时期干旱胁迫对春玉米生长发育和产量的影响.结果表明：与水分适宜对照（CK）相比,三叶-拔节期遭受干旱胁迫后,全生育期推迟13 d,至拔节普遍期,株高偏低29.8%,叶面积偏小41.2%,复水后,株高和产量得到较大程度恢复,果穗性状和最终产量差异不大;拔节-吐丝期遭受干旱胁迫后,全生育期缩短7 d,至吐丝普遍期,株高偏低18.6%,叶面积偏小14.1%,果穗长、穗粒数、果穗干质量、穗粒质量分别下降6.9%、19.1%、28.1%和29.4%,空秆率增加13.3%;吐丝-乳熟期遭受干旱胁迫后,全生育期缩短15 d,生长至乳熟普遍期,株高偏低2.3%,叶面积偏小37.3%,果穗长、穗粒数、果穗干质量、穗粒质量分别下降9.2%、24.1%、30.8%和27.9%,空秆率增加24.5%.拔节-吐丝期、吐丝-乳熟期干旱胁迫处理并复水后,玉米株高恢复不明显,产量降幅显著.     

Contingent productivity responses to more extreme rainfall regimes across a grassland biome

Climate models predict, and empirical evidence confirms, that more extreme precipitation regimes are occurring in tandem with warmer atmospheric temperatures. These more extreme rainfall patterns are characterized by increased event size separated by longer within season drought periods and represent novel climatic conditions whose consequences for different ecosystem types are largely unknown. Here, we present results from an experiment in which more extreme rainfall patterns were imposed in three native grassland sites in the Central Plains Region of North America, USA. Along this 600 km precipitation–productivity gradient, there was strong sensitivity of temperate grasslands to more extreme growing season rainfall regimes, with responses of aboveground net primary productivity (ANPP) contingent on mean soil water levels for different grassland types. At the mesic end of the gradient (tallgrass prairie), longer dry intervals between events led to extended periods of below-average soil water content, increased plant water stress and reduced ANPP by 18%. The opposite response occurred at the dry end (semiarid steppe), where a shift to fewer, but larger, events increased periods of above-average soil water content, reduced seasonal plant water stress and resulted in a 30% increase in ANPP. At an intermediate mixed grass prairie site with high plant species richness, ANPP was most sensitive to more extreme rainfall regimes (70% increase). These results highlight the inherent complexity in predicting how terrestrial ecosystems will respond to forecast novel climate conditions as well as the difficulties in extending inferences from single site experiments across biomes. Even with no change in annual precipitation amount, ANPP responses in a relatively uniform physiographic region differed in both magnitude and direction in response to within season changes in rainfall event size/frequency.     

Tree resilience to drought increases in the Tibetan Plateau

Forests in the Tibetan Plateau are thought to be vulnerable to climate extremes, yet they also tend to exhibit resilience contributing to the maintenance of ecosystem services in and beyond the plateau. So far the spatiotemporal pattern in tree resilience in the Tibetan Plateau remains largely unquantified and the influence of specific factors on the resilience is poorly understood. Here, we study ring‐width data from 849 trees at 28 sites in the Tibetan Plateau with the aim to quantify tree resilience and determine their diving forces. Three extreme drought events in years 1969, 1979, and 1995 are detected from metrological records. Regional tree resistance to the three extreme droughts shows a decreasing trend with the proportion of trees having high resistance ranging from 71.9%, 55.2%, to 39.7%. Regional tree recovery is increasing with the proportion of trees having high recovery ranging from 28.3%, 52.2%, to 64.2%. The area with high resistance is contracting and that of high recovery is expanding. The spatiotemporal resistance and recovery are associated with moisture availability and diurnal temperature range, respectively. In addition, they are both associated with forest internal factor represented by growth consistence among trees. We conclude that juniper trees in the Tibetan Plateau have increased resilience to extreme droughts in the study period. We highlight pervasive resilience in juniper trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes.     

Multiscale topoedaphic heterogeneity increases resilience and resistance of a dominant grassland species to extreme drought and climate change

It is argued that the inclusion of spatially heterogeneous environments in biodiversity reserves will be an effective means of encouraging ecosystem resilience and plant community conservation under climate change. However, the resilience and resistance of plant populations to global change, the specific life‐history traits involved and the spatial scale at which environmentally driven demographic variation is expressed remains largely unknown for most plant groups. Here we address these questions by reporting an empirical investigation into the impacts of an unprecedented 3‐year drought on the demography, population growth rates (λ) and biogeographical distribution of core populations of the perennial grassland species Austrostipa aristiglumis in semiarid Australia. We use life‐history analysis and periodic matrix population models to specifically test the hypothesis that patch‐ and habitat‐scale variation in vital life‐history parameters result in spatial differences in the resilience and resistance of A. aristiglumis populations to extreme drought. We show that the development of critical soil water deficits during drought resulted in collapse of adult A. aristiglumis populations (λ?1), rapid interhabitat phytosociological change and overall contraction towards mesic refugia where populations were both more resistant and resilient to perturbation. Population models, combined with climatic niche analysis, suggest that, even in core areas, a significant reduction in size and habitat range of A. aristiglumis populations is likely under climate change expected this century. Remarkably, however, we show that even minor topographic variation (0.2–3 m) can generate significant variation in demographic parameters that confer population‐level resilience and resistance to drought. Our findings support the hypothesis that extreme climatic events have the capacity to induce rapid, landscape‐level shifts in core plant populations, but that the protection of topographically heterogeneous environments, even at small spatial scales, may play a key role in conserving biodiversity under climate change in the coming century.     

硅对干旱胁迫下玉米水分代谢的影响

利用盆栽试验研究了施硅(K2SiO3)对玉米植株水分代谢的影响.结果表明:施硅降低了干旱胁迫下玉米植株的气孔导度,降低了干旱胁迫早期到中期的蒸腾速率,保持了干旱胁迫后期较高的蒸腾速率,从而导致施硅玉米植株的叶片含水量和水势高于对照.由于植株的水分状况改善,施硅玉米植株生物量高于对照.硅增强玉米植株的抗旱性,而提高植株保水能力是硅提高抗旱性的重要原因.     

Negative effects of climate warming on maize yield are reversed by the changing of sowing date and cultivar selection in Northeast China

Northeast China (NEC) accounts for about 30% of the nation's maize production in China. In the past three decades, maize yields in NEC have increased under changes in climate, cultivar selection and crop management. It is important to investigate the contribution of these changing factors to the historical yield increases to improve our understanding of how we can ensure increased yields in the future. In this study, we use phenology observations at six sites from 1981 to 2007 to detect trends in sowing dates and length of maize growing period, and then combine these observations with in situ temperature data to determine the trends of thermal time in the maize growing period, as a measure of changes in maize cultivars. The area in the vicinity of these six sites accounts for 30% of NEC's total maize production. The agricultural production systems simulator, APSIM‐Maize model, was used to separate the impacts of changes in climate, sowing dates and thermal time requirements on maize phenology and yields. In NEC, sowing dates trended earlier in four of six sites and maturity dates trended later by 4–21 days. Therefore, the period from sowing to maturity ranged from 2 to 38 days longer in 2007 than it was in 1981. Our results indicate that climate trends alone would have led to a negative impact on maize. However, results from the adaptation assessments indicate that earlier sowing dates increased yields by up to 4%, and adoption of longer season cultivars caused a substantial increase in yield ranging from 13% to 38% over the past 27 years. Therefore, earlier sowing dates and introduction of cultivars with higher thermal time requirements in NEC have overcome the negative effects of climate change and turned what would have otherwise been a loss into a significant increase in maize yield.