Combating heat at cities

Extreme heat refers to higher temperatures relative to the normal conditions or average for a particular geographical area, while a heatwave or extreme heat event refers to a prolonged period of extreme heat. The standards that define extreme temperature levels and the period of a heatwave vary across different environments. The elevated temperatures of heatwaves are exacerbated by elevated humidity, which hinders the human body’s ability to cool off by sweating. The incidence of extreme heat events has increased dramatically as a result of global warming caused by ongoing emissions of greenhouse gases (GHGs) that trap heat and warm the planet (figure 1.1). Already, 30 percent of the global population is exposed to potentially lethal temperatures for 20 days a year; this is estimated to increase to a staggering 48 percent by the close of the century, even assuming substantial efforts are undertaken to curtail greenhouse gas emissions (Mora et al. 2017). Today, 1.7 billion people are exposed to extreme heat in cities (Tuholske et al. 2021). The urban built environment characterized by impermeable and nonreflective surfaces, designs that ignore airflow, and, often, a lack of vegetation and water features creates heat reservoirs, trapping heat and raising local temperatures relative to surrounding areas. This phenomenon, known as the urban heat island (UHI) effect (Roberts et al. 2023), is further exacerbated by the extensive use of air conditioning and motor vehicles, which also raise temperatures (Deuskar 2022). The UHI effect can cause temperatures in cities to be as much as 10°C higher than in nearby areas, significantly amplifying heat-related risks for urban dwellers (Shandas et al. 2019). Exposure to extreme heat presents a wide range of challenges for public health, labor productivity, economic growth, and other vital societal priorities. Extreme heat is associated with increased rates of hospitalization and emergency room visits, accidents (Park, Pankratz, and Behrer 2021; Wu, Zaitchik, and Gohlke 2018), violence, risk of cardiorespiratory and other diseases, mental health challenges (Burke et al. 2018), and health care costs. Between 2000 and 2019, heat was responsible for approximately 489,000 excess deaths each year globally (Zhao et al. 2021) an estimate that may be too low because of contextual differences in reporting standards, definitions, and impacts that complicate the estimation of overall mortality and morbidity from extreme heat. Additionally, studies show that extreme heat hurts the economy. By 2050, UHI effects could cause cities to lose an average of 1.4–1.7 percent and as much as 10 percent of their gross domestic products (Estrada, Botzen, and Tol 2017).1 One mechanism through which such losses occur is declines in productivity. The International Labor Organization estimates that extreme heat will lead work hours to diminish by 2 percent between 2019 and 2026 (ILO 2019b).

source :

https://openknowledge.worldbank.org/entities/publication/c4cc3e20-c5f0-4469-baea-14dc32021711