Cities would literally be Much Cooler with More Trees Around : Daily Current Affairs

Date: 09/02/2023

Relevance: GS-3: Biodiversity and Environment

Key Phrases: zero carbon emissions, urban heat islands, premature deaths, flash flooding, El Niño, 3-30-300 rule.

2022 was Europe’s hottest summer on record, leading to more than 20,000 excess deaths across western Europe, and this summer could be even worse with the return of El Niño.

El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean.
El Niño is the “warm phase” of a larger phenomenon called the El Niño-Southern Oscillation (ENSO).
El Niño events occur irregularly at two- to seven-year intervals.
During an El Niño event, westward-blowing trade winds weaken along the Equator.

The effects may be felt most in our cities, which are on average 1.5° Celsius warmer than surrounding areas due to so-called urban heat islands (UHIs).
That’s when building materials (concrete, asphalt, metal) and machinery (cars, trucks, air-conditioners) absorb and produce heat, turning city blocks into baking ovens.
The heat is just one way in which cities can be unhealthy places to live; 4.3% of premature deaths in cities during the summer months are attributable to UHIs.
Outdoor air pollution kills more than 4 million people a year. Noise causes the loss of more than 1.8 million healthy life years in Europe.
Studies have shown that people who live in cities have smaller carbon footprints than those in the suburbs and countryside.
Urban dwellers walk more, cycle more, and use public transport more than their suburban and rural counterparts.
They also live in smaller homes with less stuff. Encouraging denser living could be a key part of the race to net zero carbon emissions.
But if we’re going to convince people to live in them, we have to make cities more livable first.

The urban heat island effect is a phenomenon whereby cities experience higher air temperatures than the surrounding countryside. This effect can be quite noticeable.
On average, cities tend to be 1-7°F warmer during the daytime.
This difference continues well into the night, during which cities can still be as much as 5°F warmer than the areas around them.
Scientists refer to areas afflicted by these higher temperatures as urban heat islands.

As cities grow, new development such as roads and buildings displace natural surfaces like trees, ponds, and soil.
This change in the local environment results in a corresponding change in the local climate.
That’s because these natural surfaces help moderate air temperatures.
Trees and other plants, for instance, can lower air temperatures by providing shade.
This vegetation, along with soil and water, also helps cool nearby air through “evaporative cooling,” which is a natural process by which evaporating water absorbs heat (much like sweat cools the human body).
The man-made surfaces that replace these features, however, tend not to have cooling effects.
Instead, they tend to absorb and re-emit more heat, which makes their surroundings warmer too.
Though much of that heat comes from the sunlight those surfaces receive, another source of heat is human activities—like power generation and the use of cars and air conditioners.
The geometry of cities also contributes to heat islands: the narrow spaces between tall structures, known as urban canyons, can block wind and trap heat.

A new study published in The Lancet shows that increasing tree canopy cover to 30% of the city could reduce premature summer deaths in cities by about 40%, by reducing the temperatures through a combination of shading, evaporating water, and removing sources of heat such as concrete and asphalt.
Satellite data has shown that 30% of tree coverage is a feasible target in the 93 cities covered in the study, but the average in Europe is still only 14.9%.
In a 2011 study, Soares estimated the cost of maintaining trees at $1.9 million a year. The benefits came in at $8.4 million.
Not only are streets more aesthetically pleasing when they’re lined with trees, but there are proven benefits for mental health.
Urban green spaces are also associated with a lower prevalence of diabetes, heart problems, better birth outcomes, and improved cognitive functioning.
Plus, trees are handy carbon stores that can also help prevent flash flooding—another climate risk.

Cities have historically given priority to space for vehicles. Wide roads and car parks could be reduced to make way for foliage but, as battles over cycle lanes in different cities have shown, there is little space left for trees to be planted.
There is also the expense. After buying and planting, new trees require maintenance.
Like people, they can also find the urban environment difficult to survive in.

The vital thing will be to ensure there’s an equitable distribution of trees throughout the city.
One huge forest park won’t have the same beneficial effects as many tree-lined streets.
Richer areas already tend to be greener than poorer ones, so there’s a social justice element too in ensuring everyone has equal access to nature.
3-30-300 rule: Cecil Konijnendijk, professor of urban forestry at the University of British Columbia, has suggested a 3-30-300 rule: Everyone should be able to see 3 trees from their window, live in a neighborhood with 30% tree cover and be 300 meters from a green space.

Making our cities more livable and sustainable will involve a lot of difficult decisions, about more than plant life. But considering trees can take decades to grow, we should get planting now.

Source: Live-Mint

Mains Question:

Q. What is Urban Heat? How trees could help cool cities, reduce pollution and improve our Mental and Physical Health? (250 words).