Climate variations intensify heat waves, endangering public health and exacerbating social inequalities. American researchers are studying the impact of these phenomena on different populations and exploring solutions to strengthen the climate resilience of urban communities.
Heat waves, while less spectacular than other extreme weather events, are just as deadly. The thermal stress they cause puts a strain on the human body, particularly when high humidity reduces the effectiveness of transpiration. In many parts of the world, extreme heat already causes more deaths than floods, wildfires and hurricanes combined.
Researchers at the Pacific Northwest National Laboratory (PNNL) have studied how heat waves evolve under climate change. Their computer simulations reveal that uneven warming of the Pacific Ocean is intensifying heat waves. atmospheric Rossby waves. These air movements can stagnate over certain regions for long periods, creating conditions conducive to oppressive heat.
Models predict that the amplitude of these waves could double by 2080-2099 compared to the period 1995-2014. Combined with other factors such as soil drought, this development suggests a significant increase in the intensity of heat waves, particularly in the northwestern states of the United States.
Urban areas, particularly vulnerable
City dwellers are especially exposed to heat stress. The phenomenon ofurban heat island is explained by the concentration of buildings and paved surfaces which absorb heat during the day and release it at night. A PNNL study of several large cities in the eastern United States found that city dwellers experience two to six additional hours of uncomfortable heat (above 26.7°C) compared to rural areas. surrounding areas.
The temperature difference between urban and rural areas increases during heat waves. An increase of 6.1°C compared to seasonal norms translates into three additional hours of uncomfortable heat per day for city dwellers.
Inequalities in the face of heat
Even within cities, significant disparities are observed between neighborhoods. Areas with a high concentration of concrete and little green space experience significantly higher temperatures. These differences often follow socio-economic and racial fault lines, inherited in particular from the redlining policies of the 1930s.
An analysis of 481 large U.S. cities found that the average black resident lives in an area where heat stress is 0.28°C higher than the city average. Conversely, the average white resident enjoys a 0.22°C cooler environment. Similar gaps are observed between income groups, with poorer populations generally more exposed to heat.
Towards better climate resilience
A detailed understanding of the mechanisms of heat waves and their differentiated impacts on populations makes it possible to guide adaptation efforts. The U.S. Department of Energy supports several initiatives to collect local data and help communities assess their specific needs.
Four integrated urban laboratories have been implemented in Baltimore, Chicago, southeast Texas and Arizona. These structures bring together varied expertise (universities, national laboratories, local governments, neighborhood organizations) to study the interactions between the urban environment and the climate system.
Six Climate Resilience Centers were also created across the country. Their mission is to train the next generation of scientists and technicians, while putting the tools of climate science at the service of local decision-making.
Illustration caption: Photo of part of New York City with a heat map overlaid, with red indicating the hottest areas. Credit: Timothy Holland | Pacific Northwest National Laboratory
