To reduce the dangerous effects of heat domes and the urban heat island effect, cities in the US are actively planting trees, painting sidewalks white and reducing concrete/cement surfaces.
In 2013, Los Angeles became the first major city to pass a requirement that all new homes must have heat-resistant roofs. Since then, the city, which is expected to see a spike in days above 35 degrees Celsius by 2050, has implemented many other cooling initiatives, including painting sidewalks white and expanding the Green Standard Construction Regulations to require Heat-resistant roofs in non-residential buildings, according to BBC.
However, despite efforts to reduce heat, people in the city still suffer from problems related to high temperatures. One study found that the number of emergency calls related to extreme heat in Los Angeles from 2018 to 2022 was directly correlated with the number of days of 32 degrees Celsius or higher.
In June, a prolonged heat dome brought dangerous temperatures to the western United States. People experienced temperatures up to 46.1 degrees Celsius in California, Nevada, Utah and Arizona. The most recent heat wave shows the importance of being prepared for hot weather in cities. About 80% of the US population lives in urban areas, where the heat island effect can be worsened by hot weather. Urban heat islands are densely populated areas with few trees and lots of concrete and asphalt that absorb solar energy. When the Sun sets, man-made materials release stored heat, causing the city to remain hot into the evening. Urban heat island temperatures can be up to 11 degrees Celsius higher than in less populated areas. As the number of hot days continues to increase, US city governments are applying many measures to deal with hot weather.
Plant a tree
Planting trees helps reduce ground and air temperatures by providing shade and cooling through evaporation and transpiration. Research shows that urban forests have an average temperature of 1.6 degrees Celsius lower than urban areas without forests. Many cities across America are implementing the greening movement. Austin, Texas, aims to green 50% of the city by 2050. In Phoenix, Arizona, the hottest city in the US, the tree planting movement provides shade for some residential areas. Authorities have approved an investment of more than 1.4 million USD to plant 1,800 trees across the city to provide cool corridors.
In Tuscon, Arizona, drought makes planting more difficult in low-income neighborhoods where residents don’t have the money to plant and care for plants in their gardens. The city conducts a refund program of up to 2,000 USD to support people in installing rainwater collection systems for watering plants.
Trees are planted not only on the ground but also on the roof. In 2017, San Francisco required at least 15% of the roof surface area of new buildings larger than 1,858 m2 to be covered with photovoltaic cells or trees. A large number of buildings in the city have green roofs, not only removing heat from the air through evaporation, but also reducing the roof surface temperature. On a hot summer day, the temperature of a green roof can be cooler than the surrounding air while a regular roof can be hotter than 40 degrees Celsius.
White paint
A recent study found that white-painted roofs reflect 80% of sunlight and are 31 degrees Celsius cooler on summer afternoons. This is not a new idea. Cities in North Africa and Southern Europe have applied it for centuries. Currently, this solution is being applied in the US. New York City recently painted more than 930,000 square meters of roofs white, helping to reduce internal temperatures by 30%. The state of California also updated its building codes to encourage heat-resistant roofs.
Scientists around the world develop a variety of cooling coatings for sidewalks, roofs and walls, containing special additives to reflect heat from the Sun. They can help pedestrians feel 1.5 degrees Celsius cooler, while also reducing surface heat absorption, meaning that at night, light-colored surfaces will not release heat stored during the day. Los Angeles has been experimenting with cooling paint, but has encountered some limitations. The paint the city uses costs $40,000 per mile (1.6 km) and only lasts seven years. In 2020, a study in Phoenix showed that covering sidewalks with cooling paint helps lower the street’s surface temperature. The city then decided to make the program permanent.
Collect data
Data collection plays an important role in future planning for heat stress. In 2022, 60 volunteers measured morning, afternoon and evening temperatures in Clark County, which includes Las Vegas, in a heat mapping study funded by the US National Oceanic and Atmospheric Administration. Maps created from that data show temperatures rising the most in north and east Las Vegas as well as downtown, which could be as much as 6 degrees Celsius hotter than elsewhere in the city. Clark County is now using data to find ways to reduce heat, including building public cooling centers and planting trees.
The City of Albuquerque, New Mexico, is teaming up with local volunteers to map temperature and humidity through the distribution of specially designed heat sensors. Residents drive or cycle around predetermined routes twice a day to record more than 67,000 temperature points. The map reveals a difference of up to nearly 9.4 degrees Celsius in different areas of the city, the hottest places are the central area and residential areas next to the highway and the people most affected are the community. low income.
Other solutions
Heat planning is extremely important for cities like Las Vegas. This is the second fastest warming city in the US after Reno, Nevada, with temperatures in June reaching 46.1 degrees Celsius. Experts have worked with city authorities over the past six years to develop the plan Heat protection by 2050. Heat mitigation plans include planting low-cost drought-resistant trees to provide shade, reducing concrete or cement surfaces and designing buildings with roofs.