Roots of Resilience: How Trees Can Help Fight Rising Heat In Arid Cities

Via The Nature Conservancy, a report on new science that shows increasing greening programs in arid cities could reduce air temperatures near people’s homes by an average of 0.5 degrees C:

As the world grapples with increasingly common and devastating heat waves, new science shows that nature-based solutions—like tree planting and water conservation—are important and cost-effective ways to help protect vulnerable, frontline communities in arid locations from the worst effects of rising heat. But time is of the essence.

The Gist

For the report, “Roots of Resilience: Using Trees to Mitigate Rising Heat in Arid, Frontline Communities,” researchers assessed 61 large cities (> 3 million population) and found that citizens of arid cities have on average 1.5% tree cover in their neighborhood, while the average for citizens in semi-arid cities is 4.2%.

That’s a lot of room for improvement. And researchers estimate that targeted urban greening programs could realistically increase tree canopy to 7.1% in arid cities and 7.3% in semi-arid cities.

According to researchers, such an increase from greening programs in arid cities, like Athens and Phoenix, would meaningfully reduce air temperatures near people’s homes by an average of 0.5?C. The biggest potential decreases in air temperatures near people’s homes are in urban areas like Kabul (1.2?C) and Damascus (1.1?C), which currently have arid climates and limited tree cover.  

The Big Picture

According to the Intergovernmental Panel on Climate Change, life-threatening heat and humidity are expected to impact between half to three-fourths of the global population by 2100.

Cities, which are currently home to more than half the world’s population and will add another 2.5 billion people by 2050, will be exposed to double the intensity of heat stress compared to rural surroundings.

“Most at risk,” notes report co-author Rob McDonald, TNC’s lead scientist for nature-based solutions, “are what we characterize in the report as ‘frontline communities,’ or those impacted first and worst by the impacts of extreme heat. These are communities that are often home to people of lower socioeconomic status who are most vulnerable to climate change and least empowered to adapt.”

There is a catch, though, to the use of trees as nature-based solutions in arid cities: water scarcity.

Map of all continents showing tree canopy and water need in 31 cities
Tree canopy enhancement potential and irrigation demand rate for large (> 3 million) functional urban areas in arid or semi-arid climates.

Researchers estimate that increasing tree canopy cover in the 61 cities identified in this report to the maximal potential would also increase aggregate water demand by 3,200 million cubic meters per year. To address that concern, the report notes that the use of location-appropriate, drought-tolerant species could reduce this water demand to 1,500 million cubic meters per year—with especially large water savings possible in semi-arid climates.

Therefore, researchers stress that any plans to increase tree canopy cover in these cities must provide viable options for overcoming potential water limitations and increasing tree equity.

In arid climates where irrigation for trees will be essential, recommendations include leveraging alternative sources of water, such as the reuse of stormwater, as well as wastewater or grey water.

The Takeaway

“Extreme heat is the world’s first widespread climate crisis,” says McDonald. “We’re already feeling it, and the years of coming extreme heat will impact water-scarce cities hardest—combining twin threats of deadly heat with water scarcity from declining precipitation. Science shows trees and other nature-based solutions to climate change have roles to play in reducing heat, if water demands are minimized and water recycling is promoted.”

Illustration of a tree with list of benefits

“Roots of Resilience” identified 96 million people in in arid and semi-arid regions where frontline communities are at risk of extreme heat, but water availability may limit their options to use trees to mitigate heat from climate change.

“Actions to address extreme heat are urgently needed today,” says report co-author Eleni Myrivili, the United Nation’s first Chief Heat Officer. “As those most at risk, frontline communities must be explicitly made the focus of funding and action. It takes years for trees to mature into a robust canopy. Climate change is already here, and every year countries wait to ‘green’ frontline communities is a missed opportunity to save and improve lives.”



This entry was posted on Saturday, September 14th, 2024 at 10:23 am and is filed under Extreme Heat, Green Design.  You can follow any responses to this entry through the RSS 2.0 feed.  Both comments and pings are currently closed. 

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BLACK SWANS GREEN SHOOTS
Black Swans / Green Shoots examines the collision between urbanization and resource scarcity in a world affected by climate change, identifying opportunities to build sustainable cities and resilient infrastructure through the use of revolutionary capital, increased awareness, innovative technologies, and smart design to make a difference in the face of global and local climate perils.

'Black Swans' are highly improbable events that come as a surprise, have major disruptive effects, and that are often rationalized after the fact as if they had been predictable to begin with. In our rapidly warming world, such events are occurring ever more frequently and include wildfires, floods, extreme heat, and drought.

'Green Shoots' is a term used to describe signs of economic recovery or positive data during a downturn. It references a period of growth and recovery, when plants start to show signs of health and life, and, therefore, has been employed as a metaphor for a recovering economy.

It is my hope that Black Swans / Green Shoots will help readers understand both climate-activated risk and opportunity so that you may invest in, advise, or lead organizations in the context of increasing pressures of global urbanization, resource scarcity, and perils relating to climate change. I believe that the tools of business and finance can help individuals, businesses, and global society make informed choices about who and what to protect, and I hope that this blog provides some insight into the policy and private sector tools used to assess investments in resilient reinforcement, response, or recovery.