Some US cities are trying new ways to fight extreme heat. One way is planting more trees. Another is painting streets white.
In 2013, Los Angeles was the first big city to make a law. The law says all new homes must have a cool roof. Los Angeles expects many more very hot days above 35C (95F) by 2050. So the city started other cool initiatives too. Like painting sidewalks white. And expanding building codes for cool roofs.
Even with these efforts, people still have heat issues. A study found a direct link. When days reached 32C (90F) or higher in LA from 2018-2022, there were more emergency calls due to extreme heat.
An expert says there are huge opportunities to reduce heat in US cities. But he is frustrated. The knowledge exists, but not enough is being done.
In June, a heat dome brought very dangerous temperatures to the western US. People experienced up to 46.1C (115F) in some states. The National Weather Service warned temperature records could be tied or broken. They said there would be little relief from the heat at night.
This recent extreme heat shows cities must get ready for hot weather. But some experts say cities are not prepared enough. Even though the science on how to cool cities is well known.
Around 80% of Americans live in cities. The heat island effect makes hot weather worse in cities. Heat islands are crowded areas with few trees. They have a lot of dark concrete and asphalt that absorbs the sun’s energy. At night, these materials release the stored heat. So cities stay hot, even when the sun goes down. City heat islands can be up to 20F hotter than less crowded areas.
Vulnerable groups are impacted more by the heat. This includes elderly people, children, and low-income populations. The heat can even harm newborn babies.
Many US cities continue to have record-breaking, extremely hot days that threaten lives. But researchers say many cities are still not prepared enough. In 2022, scientists looked at city plans for the 50 biggest US cities. Most plans mentioned heat, but few included good strategies to address it.
A researcher says if city plans do not fully describe the heat problem, we cannot protect residents well. She says we could make existing social and environmental injustices worse.
Another study found 41 million people live where urban heat islands are extreme. This report was by Climate Central. It found 14 cities had a big difference between city temperatures and surrounding areas. These cities included Albuquerque, Bakersfield, Fresno and Las Vegas.
The expert says there is too much talk and not enough action on this issue. He says it is extremely hard to make real change happen. He says no US city is a good model for reducing extreme heat well.
But the expert is still hopeful. This is because there are things cities can do to become cooler. He thinks cities are starting to change their way of thinking about this.
Green over gray
Planting trees is widely known to lower temperatures. Trees provide shade and cooling from evaporation. Research shows urban forests are on average 2.9F cooler than areas without trees.
Because of this, many US cities have started planting more trees. Austin, Texas requires 50% tree coverage in the city by 2050. Phoenix has a reputation as the hottest US city. There, they are planting trees to shade the warmest neighborhoods. Over $1 million was approved to plant up to 1,800 trees for cool corridors.
In Tucson, Arizona, drought makes tree planting hard in low-income areas. People there cannot afford to plant or maintain trees. The city gives rebates up to $2,000 for rainwater collection systems to water trees and green spaces. They offer zero-interest loans and grants for struggling communities. They also provide workshops in Spanish.
Cities are not just planting plants on the ground. They are also putting plants on roofs. In 2017, San Francisco made a new rule. For big new buildings over 2,000 square feet, 15% of the roof must have solar panels or plants.
Some large buildings in the city already have green roofs. Green roofs remove heat from the air through evaporation. They also reduce roof surface temperatures. On hot summer days, a green roof can be cooler than the outside air. But a regular roof can be over 72F hotter.
Paint it white
A study found clean white roofs that reflect 80% of sunlight stay about 56F cooler on summer afternoons.
This idea is not new. Cities in North Africa and southern Europe have been doing this for centuries. Lehmann helped start painting white roofs in Australia in 2012. Community projects there found it cooled building insides by up to 4.5F. He says this is finally happening in the US now.
New York City recently coated over 10 million square feet of roofs white. This reduces indoor building temperatures by 30%. California updated building codes to promote cool roofs as a way to save energy.
Scientists worldwide have developed special cool paint coatings for pavements, roofs and walls. These contain additives to reflect the sun’s heat better than regular white paint. The coatings have been proven to make pedestrians feel 2.7F cooler.
The paint reduces heat absorption. So at night, the light surfaces don’t release stored heat from the day. Los Angeles has tested cool paints, but there are downsides. The paint costs $40,000 per mile and lasts 7 years. Also, Lehmann points out white roads don’t stay clean for long.
Cooling a city at night is extremely important. Staying hot at night can lead to serious health problems. Night time is also when the urban heat island effect can be at its worst.
Some places are testing painting pavements with special cool coatings. In 2020, a study in Phoenix found cool paint lowered street surface temperatures. After this, Phoenix made it a permanent program.
But it’s a complicated solution. Reports show white pavements can actually make people feel hotter. The sunlight reflects off the white ground onto people walking there. Although the pavement surface in Phoenix was 10F cooler, the air temperature 6 feet away was just 0.3F cooler.
Community participation
Collecting data plays an important role in planning for future heat.
In 2022, 60 volunteers measured temperatures in the morning, afternoon and evening across Clark County, where Las Vegas is located. This was part of a heat mapping study. The map made from this data shows elevated temperatures are worst in North Las Vegas, East Las Vegas and downtown – up to 11F hotter than other parts.
The county is now using this data to make heat reduction policies. These include community cooling centers and planting more trees.
In Albuquerque, New Mexico, the city gave special thermal sensors to local volunteers. Residents drove or biked set routes twice daily to record over 67,000 temperature points. The maps showed differences of almost 17F across parts of the city, with downtown and areas near highways being hottest.
Again, low-income neighborhoods were most affected. So the city teamed up with NASA to take satellite images overlaid with data on vulnerable communities to target these areas.
The city of Albuquerque had never collected data like this before. The data allowed the city government to plan for heat based on who needed help the most.
“It led to two important strategies we are doing now,” says the city’s sustainability officer Ann Simon. One is a program to help low-income families be more energy efficient at home and lower their energy bills by around $300 per year. So far, the city has improved 104 homes.
Simon says, “We are a small program but we just got a $2 million grant. This will help six times more families.”
NASA will also take new images of the neighborhoods again. Simon hopes this new data will help plan for the future.
Planning for the future
Planning is very important for cities like Las Vegas. Las Vegas is the second fastest warming city in the US after Reno, Nevada. Temperatures in Las Vegas reached around 115F this June.
A professor says, “A few years ago, very few cities talked about preparing for rising temperatures. It is an important step that heat is now a bigger part of the conversation.”
Lehmann has worked with Las Vegas city officials for six years. They made a plan to cool the city by 2050. In 2021, Clark County released this 2050 Master Plan. It has ideas to reduce heat. Planting shady, drought-resistant plants is one idea. Reducing paved areas is another. Designing shady buildings is also part of the plan.
Lehmann believes change will come now that the city wants it. Las Vegas has started other projects too. They opened cooling stations for homeless people during hot weather. They plan to plant 60,000 trees by 2050 for shade. At a big stadium, they will remove 1,000 parking spots to plant 1,000 trees. This is controversial because Las Vegas depends on cars.
The city works with University of Vegas engineers too. They develop a reflective coating for casino and hotel roofs. But using this coating is voluntary.
There is a lot of science on cooling cities. But the science is complex. Trees can make air feel humid, which is unhealthy. White paint on roads can still leave streets hot. Many solutions are needed. Creative thinking is required.
Lehmann stays positive despite frustrations. He says architects must reimagine the future. He wants to see how Las Vegas will look in 20 years.
