Local decision-makers looking for ways to reduce the impact of heat waves on their communities now have a valuable resource at their disposal: a new study on vegetation resilience. Researchers at Oak Ridge National Laboratory conducted a study on how vegetation survived extreme heat events in urban and rural areas across the country. The study found that vegetation, such as trees, provides a valuable cooling effect by shading surfaces, deflecting solar radiation, and releasing moisture into the atmosphere through evapotranspiration. The presence of impervious surfaces, moisture conditions, and land cover type all play a role in determining vegetation resilience to heat waves.
Published in the journal PNAS Nexus, this study is the first nationwide analysis of vegetation resilience that takes into account the impact of human-built infrastructure. Using machine learning methods, researchers examined data from 85 large cities and surrounding rural areas covering two decades. They found that factors such as impervious surfaces, moisture conditions, and land cover type all influence vegetation resilience. The study also looked at how vegetation is affected by the intensity, duration, and timing of heat waves, providing crucial insights into how ecosystems can be protected from climate change.
Lead researcher Jiafu Mao stated that the study’s findings can help urban planners understand which plants are more vulnerable to heat waves and stressors such as water availability, guiding decisions about plant selection, location, and urban design improvements. Preserving and enhancing vegetation could significantly contribute to urban sustainability, air quality improvements, and the well-being of residents. The study also builds on previous research on climate impacts in urban and rural ecosystems, showing how vegetation resilience can be improved to counteract the effects of urban heat islands.
One of the key findings of the study was the identification of a temperature threshold of 2 degrees Celsius or higher above the historical summer average persisting for four months or more as the point at which vegetation greening significantly declines. The study also revealed variations in resilience between urban and rural areas, with urban vegetation showing more resilience in the western United States due to higher urban growth temperatures and better irrigation practices. This large-scale quantification of urban and rural differences provides valuable insights for urban planners and ecosystem modelers.
The project utilized high-quality data from sources such as the Daymet4 database, MODIS Enhanced Vegetation Index, and the National Land Cover Database, as well as machine learning algorithms and high-performance computing resources. The information gathered has been used to enhance the land surface component of the DOE Energy Exascale Earth System Model, which simulates potential future climate scenarios. By capturing complex interactions between biological and environmental factors at multiple scales, the study offers a detailed understanding of how vegetation resilience can be improved to mitigate the impacts of heat waves on communities across the country.
