Early heat waves hit wheat yields hardest but boost their resilience to subsequent heat waves
Society for Experimental Biology
New research published in the Journal of Experimental Botany reveals that wheat crops are more sensitive to grain yield losses from heat waves that occur before reaching their flowering stage than those occuring later. However, exposure to heat waves early in the growing season may reduce yield losses during additional heat waves through a protective “priming” effect.
A team of researchers from the University of Lleida in Catalonia, Spain, investigated the roles of heat wave intensity, frequency, and their timing relative to crop flowering during the growing season to identify how these factors interacted to impact wheat crop yield.
Heat waves are increasing in frequency and intensity around the world, and their durations are also expanding to cover more of the wheat crop growing season, which can include the pivotal flowering stage where wheat shifts from setting grains to grain growth.
This research demonstrates that heat wave damage in wheat depends not only on the intensity of the heat wave, but also when it occurs and whether the crop has experienced a heatwave earlier in the season.
“Most studies have examined heat stress as a single event, and have done so under controlled conditions rather than under field conditions,” says co-author Dr Gustavo Slafer. “We investigated whether an earlier heat wave could alter how wheat responds to a later one during reproductive development”.
Field experiments were carried out across two growing seasons using two modern wheat varieties. Both varieties responded similarly to the heat wave treatments, despite having contrasting yield-building strategies.
Heat wave treatments were created by growing wheat inside transparent tents that created a daily temperature rise due to a greenhouse effect, and the pre-flowering and post-flowering conditions were standardised to relative heat load to allow for comparisons. Heat load was measured as the additional hourly degrees of temperature accumulated over an average day compared to the control treatment, and giving more emphasis to the heat load above 32 °C.
The major findings of this study are that wheat grain yield is more sensitive to heat waves that occur before flowering than after flowering, and that while the earlier heat waves reduced the overall number of grains produced, later heat waves reduced the weight of those grains.
Surprisingly, the team also found that when exposed to sequential heat waves in one season, wheat appears to be primed by the early pre-flowering heat waves to reduce the impact of the later post-flowering heat waves, compared to those experiencing only post-flowering heat waves.
Priming is a type of physiological memory, where exposure to an initial stress can trigger protective responses that remain partly active, allowing the plant to respond more effectively to a later stress.
“To our knowledge, this is the first evidence of this type of antagonistic interaction between successive heat waves in field-grown crops,” says Dr Slafer.
These findings can help farmers to improve predictive models of crop yields and help identify where and when adaptation measures will be most useful.
“This study reinforces the importance of protecting wheat during the stages when grain number is determined, particularly around flowering,” says Dr Slafer. “The most effective adaptation measures are therefore likely to be those that reduce exposure during the most sensitive reproductive stages.”
These findings are expected not to be unique to wheat and may be relevant to other temperate field crops such as barley, oats and rye, but specific heat thresholds are likely to differ among a wide range of crop species.
This study also highlights the importance of considering multiple heat wave events when predicting crop yield damage under future climate scenarios.
“Wheat is one of the world’s most important staple crops, so safeguarding its yield under climate change is a major priority,” says Dr Slafer. “As a crop of temperate origin, wheat is generally less adapted to high-temperature episodes than crops with tropical origins, such as maize or rice.”
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Additional authors: Breno Bicego and Roxana Savin
The Journal of Experimental Botany is a partially open access journal published on behalf of the Society for Experimental Biology by Oxford University Press. The aim of the Journal of Experimental Botany is to publish papers that advance our understanding of plant biology.
The graphs show that even though the expansion and transport histories of the magnetic fields and reconnection timings differed substantially, the reconnection rates were strikingly similar once a current sheet had formed.
Credit
Taichi Morita/Kyushu University
Journal
Journal of Experimental Botany
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Heat waves at pre-anthesis, post-anthesis, and sequentially across both stages on wheat yield under field conditions
on Date
18-Sep-2026
Hot new dataset focuses on human health
Enhanced dataset is an important tool for urban heat and health research
Heat stress is a leading cause of weather-related deaths and can be especially dangerous in cities where phenomena like urban heat islands drive temperatures higher than surrounding rural areas. Now a new dataset developed by the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR) aims to provide city governments and health officials with information that could minimize heat impacts on residents.
The layout of a city including the height and density of buildings can affect not just the number on the thermometer, but whether it feels cooler or hotter due to factors like wind and shade. This means more information than just temperature is needed to understand the true impacts of extreme heat on residents.
Researchers at NSF NCAR, Emory University, and University of North Carolina at Chapel Hill believed high-resolution urban meteorology datasets could help and began by focusing on Atlanta. The result is the High-resolution Urban Meteorology for Impacts Dataset for Atlanta Metropolitan Region (HUMID-Atlanta).
“This is a useful tool in actually quantifying how human beings experience heat in an urban environment and how factors like wind or humidity influence the impacts,” said Tzu-Shun Lin, an NSF NCAR scientist and lead author of the paper. “HUMID-Atlanta is just the first dataset of its kind. We’re already talking with other major cities and looking into the possibility of creating a version for the entire conterminous U.S.”
This research was funded by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases and is published in the journal Scientific Data.
Adding in the atmosphere
To create HUMID-Atlanta, Lin and his colleagues started with an existing dataset called HUMID that was also developed at NSF NCAR. The HUMID dataset was created using an offline simplistic urban model combined with measurements of temperature and humidity for the years 1980-2018. While it was an important research advancement, it did not capture how the atmosphere interacts with the urban environment.
To improve HUMID, the research team coupled it with NSF NCAR’s Weather Research and Forecasting model (WRF), piloting the method on the Atlanta metropolitan area. WRF has the ability to incorporate more details about an urban environment through the WRF-Urban extension. Adding characteristics like building height makes it so HUMID-Atlanta can capture details such as how wind moves around buildings and influences cooling, a factor that can change how humans are affected by heat.
The resulting enhanced dataset analyzed the years 2010-2023 and can be used to cross-reference records, such as hospitalizations, with detailed heat data from the same time period. This can help researchers identify what mix of weather and infrastructure leads to spikes in heat stress. In turn, identifying when and where dangerous conditions are likely to occur can help with planning and interventions that could reduce residents' exposure to extreme heat.
HUMID-Atlanta is publicly available. Lin and other NSF NCAR researchers are continuing to improve the method and have already extended the HUMID-Atlanta dataset through the year 2025. There are plans to use the method for other large cities, the entire U.S., and possibly even globally. Lin believes this method could also be further developed to forecast future meteorological changes and serve as a potential tool for early warning systems for extreme heat action days.
Focusing on health
HUMID-Atlanta is already being used to understand and assess heat-health impacts in urban environments. Andrew Newman, an NSF NCAR senior scientist and co-author of the paper, is working with colleagues at Emory University to help them use the dataset to better understand the impacts of heat waves on human diseases such as acute kidney injury (AKI), which causes a rapid decline in kidney function.
Previous work that analyzed links between kidney diseases and heat exposure failed to capture differences in how people experience heat depending on whether they live in city centers, surrounding suburbs, or rural areas. HUMID-Atlanta is helping to narrow in on where the risks are highest and what can be done to mitigate harm to people.
“Not only is acute kidney injury a serious health concern, but the economic burden of treating those with it is substantial,”said Newman. “HUMID-Atlanta and subsequent versions have the ability to fill major gaps in heat health research. This research will ultimately support targeted outreach and education activities, guide improvements in clinical case management, and provide inputs for risk assessment and economic evaluation of heat-health impacts.”
Journal
Scientific Data
Method of Research
Computational simulation/modeling
Article Title
The High-resolution Urban Meteorology for Impacts Dataset for Atlanta Metropolitan Region (HUMID-Atlanta)
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