Cities are hotter than ever. Here are 5 things they can do about it

Another hellish summer. The double whammy caused by the climate crisis, which is human-caused, and El Nino’s arrival has led to temperatures so high that this year was downright deadly. The world’s hottest ever month has been named July 2023. UN Secretary-General Antonio Guterres described in a recent speech that this year is the beginning of “the global boiling era.”

Heat waves are given names similar to hurricanes and typhoons in some countries. Italian Meteorological Society named a recent hot spell “Cerberus” after the three-headed dog guarding hell’s gates in Dante “Inferno.”

The problem is particularly acute in densely-populated cities, where the “urban island effect” can lead to microclimates that are 10 degrees Celsius hotter than those in surrounding areas. An amateur London meteorologist first observed the phenomenon in the 1800s. It occurs in areas where there are many concrete buildings that absorb heat, asphalt surfaces, and few green spaces.

Many cities have been ill-prepared for global warming despite knowing the dangers of it for many decades. Local officials have appointed “chief heat officers” in order to accelerate “heat action planning”, while start-ups are racing to develop better air conditioners, and personal cooling devices.

Many solutions are based upon time-tested principles of design. Here are five ways cities are combating rising temperatures right now:

1. Planting trees in green spaces

Healthy canopy trees are one of the most effective and equitable defenses against urban heat islands. According to the US Environmental Protection Agency, standing under a tree is 11 to 25 degrees Celsius cooler than standing in direct sun. Apart from the instant relief of shade, a process called “evapotranspiration,” where water transfers from plants and soil into the atmosphere, also helps cool surrounding areas by up to 5 degrees Celsius (9 degrees Fahrenheit).

Barcelona, a city that has been a pioneer in urban planning, could soon be a case study for the effectiveness of trees. According to its “Tree Master Plan,” Barcelona aims at covering 30% of its area with climate-resilient plants by 2037. Today, trees such as holm oaks (as well as Aleppo Pines, Plane Trees, Cypresses, and others) line the streets of the city and its new “superilla” or superblocks. These are basically reclaimed roadways that have been transformed into tree-lined plazas. The city has only completed a few of the 503 planned superblocks in time for the grueling Spanish Summer.

2. Spraying mist

Cooling sprays are available in parks, malls and bus stops of Chinese cities such as Wuhan and Chongqing where temperatures reached 113 degrees Fahrenheit. According to China Dialogue, the sprays can be accompanied by “mist-cannons,” which are basically utility trucks with high pressure water sprayers.

The cannons, which were originally designed to combat air pollution, have been shown in a study by the Seoul National University that misting fine water particles at an optimal angle can reduce ambient temperatures as much as 7 percent.

Austria’s capital Vienna, has designated 22 areas “cool strassen”, equipped with mist showers, drinking fountains and sprinklers that activate automatically when temperatures exceed 35 degrees Celsius.

3. Awnings rolled out

A simple, inexpensive weather shield has fallen out of style due to the current architectural trend for sleek facades. Canopies are likely to be back in fashion as cities look for quick solutions to the unrelenting summer heat.

Seville, a Spanish city (sometimes called “the Iberian Oven”), has recently increased its network of large canvas shades to cover more transit stations and shelter playgrounds, hospitals, schools, and schools.

The Tel Aviv business district has installed a series canopies that are made from LumiWeave – a “smart cloth” embedded with solar cells. The awnings were designed by Israeli designer Anai green. They store solar energy in the daytime, which is used to power the LED lights that are woven into them.

4. Paint the roofs and pavements White

Residents of Greek islands will attest that painting roofs and buildings white can be a relatively cheap and easy way to protect against the hot summers. A structure with a white roof will reflect around 85% more sunlight than a roof that is dark.

A research team from Purdue University in Indiana claims to have created a “ultra-white paint” that can reflect nearly 98% of the sunlight. This paint lowers a building’s temperature by almost 20 degrees Fahrenheit compared to the surrounding area at night.

In a statement to the press, XiulinRuan, a Purdue professor of mechanical engineering, said that covering a roof of 1,000 square feet with this paint would provide 10 kilowatts in “cooling power”. This is more powerful than central air conditioners found in most homes.

The city of Los Angeles’ Bureau of Street Services, in recent years, has painted roads with a reflective white and gray coating called CoolSeal. After a cooling effect of 10 to 15 degrees Fahrenheit was observed in pilot areas, LA’s then-mayor Eric Garcetti, announced a plan for LA to cover 250 miles of roads with cooling material by the year 2028.

White is not the only pigment that cools. In the Pacoima district of LA, a pilot project is testing street coatings in different colors. StreetBond’s acrylic-based colorant, according to the manufacturer is designed to reduce the urban heat island effect of at least 10 degrees Fahrenheit.

A 2020 study in Environmental Research Letters cast doubt on this strategy, suggesting that reflective sidewalks may result in lower surface temperatures but people in these areas could feel hotter because they absorb the heat. The authors concluded that “Solar reflective surfaces are not the panacea to urban heat problems.” They also said that cities should consider how and when people use their land in order to determine which heat metric to prioritize (air, surface or radiant temperature).

5. Restoring local materials and building techniques

Growing numbers of architects and urbanists are abandoning the Western architectural tradition and embracing natural ventilation, construction techniques that are centuries old and materials such as insulating mud-bricks.

Francis Kere, Pritzker Prize winner, uses clay, laterite stone, dead wood, and eucalyptus limbs to create a feeling of spaciousness. Kere’s Burkina Faso school buildings show how to create comfortable, convivial spaces even in extreme heat without AC.

The Auroville Earth Institute in the state of Tamil Nadu is a hub for this “vernacular architecture” movement. The research center has worked with architects and builders from around the globe for nearly 40 years to learn how to create low-carbon and economical structures using compressed soil and mud. Earth bricks are more absorbent of heat and moisture than concrete, steel and glass.

Anupama Kundoo is an Indian architect who built many structures in Auroville. She is well known for her beautiful and climate-resistant buildings, which she describes as being made with “materials sourced locally.” Kundoo, who spoke at the The World Around Summit last year in the Netherlands and argued for building with materials that are abundant there, made an impressive case.

She explained that in pre-industrial architecture we used any materials. “If there was mud we used mud. If there was wood we used wood. If it was a desert, and there is no wood you build domes.

She added, “There’s a very deep connection between what you make and where you put it.”

The conclusion of the article is:

These innovative strategies can help cities cope with the heat caused by climate change. They also offer hope for a more sustainable and cooler future. Urban centers can reduce their environmental impact by planting trees, using cooling solutions, installing awnings, and painting surfaces white.

FAQs

1. How can trees reduce urban heat?Urban areas are more comfortable in hot weather when trees provide shade. They also cool the area through a cooling process known as evapotranspiration.
2. What is the effect of white surfaces on albedo?The albedo is the ability for white surfaces to reflect light, which reduces heat absorption. This keeps temperatures down.
3. Reflective sidewalks: an effective way to combat urban heatA study from 2020 found that while they can reduce surface temperatures, the impact of their use on human comfort is dependent on a variety of factors.
4. What traditional building techniques can help in hot climatesConstruction methods and materials that are traditional can be used to create structures that are climate resilient, reducing the need for air conditioning.
5. What role does local material play in sustainable architectureBy using materials that are readily available, you can reduce the environmental impact and increase sustainability.