Temperatures are rising around the world, with 2023 recently confirmed as the hottest year on record. A new study finds that bringing nature into cities can help lower temperatures during heat waves. If you're lucky enough to live near a forested area, you'll know that one of the best ways to escape the midday heat while strolling is to head toward tree cover. Living in a concrete jungle may have fewer options than living in the suburbs, but even a trip to a local park or botanical garden can help keep you cool.
In fact, research led by the University of Surrey in the UK found that botanic gardens can lower air temperatures within cities by 5°C. The cooling effects of wetlands and rain gardens are no less impressive, at 4.7°C and 4.5°C respectively. Trees planted along streets can also reduce temperatures by 3.8°C, while urban parks can reduce temperatures by 3.2°C.
Founding Director of the Global Center for Clean Air Research, Professor and Chairman of Air Quality and Health, and Institute for Sustainab at the University of Surrey Professor Prashant Kumar, co-director of EIU, said: "We all know that green space and water cool cities. However, this study gives us the most comprehensive information yet. What's more, we can explain why. From trees providing shade, to evaporating water cooling the air."
The document pointed out that on July 19, 2022, the temperature of 40.3°C (104.5°F) in the UK broke the historical record. In the same year, approximately 62,862 people died from summer heat across Europe, and the 2003 heat wave in Europe led to drought and crop failure, causing economic losses of 16 billion euros. The team of 29 scientists from the UK, Australia, Brazil, China, Hong Kong and the United States also said that the IPCC believes that "green and blue urban infrastructure elements are particularly effective in reducing urban air temperatures".
From more than 27,000 research papers, the researchers selected 202 for meta-analysis based on categories of urban green, blue, and gray infrastructure (including parks, engineered greening projects, wetlands, green walls, parks, and botanical gardens).
For example, trees and plants help reduce heat by reducing the amount of sunlight that reaches the ground directly, while also releasing moisture into the air. The water body cools the surrounding environment through "evapotranspiration, shading, albedo effects, groundwater recharge and temperature buffering" and also acts as a radiator, cooling during the day and providing warming potential at night. Green roofs and walls not only help insulate buildings but also reduce heat gain, and vegetation also acts as a wind barrier for natural ventilation.
We've seen many building projects around the world incorporate large amounts of greenery, both to enliven facades and promote local cooling, while also providing beneficial landscaping benefits. The researchers concluded that "all types of urban green, blue, and gray infrastructure can bring cooling effects, and nature needs to be returned to densifying and expanding cities, and every opportunity must be seized to expand plant coverage on the ground, podiums, walls, and roofs."
But they also recognize that there is no simple solution that will fit every location and that much depends on effective planning - "Before selecting suitable urban green, blue and gray infrastructure interventions, it is necessary to assess the local context, environmental conditions, available resources and budgets to ensure their long-term effectiveness and avoid possible drawbacks."
Professor Maria de Fatima Andrade, from the Department of Atmospheric Sciences at the University of São Paulo in Brazil, added: "Our paper confirms how many ways there are to keep cool. But it also reveals how much more needs to be done. Institutions around the world need to invest in the right research, as our study clearly shows that there is no one-size-fits-all solution. It depends on what works for your community."
The research was published publicly through the journal Innovation.