Forests are intrinsic to making cities and human settlements inclusive, safe, resilient, and sustainable.

World Cities Day, observed annually on October 31st, is a United Nations initiative to promote international cooperation to address the challenges and opportunities urbanization presents. This day serves as a platform to raise awareness about the role of cities in sustainable development and to inspire actions that make cities more inclusive, resilient, and sustainable. It also encourages cities worldwide to share innovative solutions and best practices for urban development, fostering a sense of global solidarity in addressing the urban challenges of the 21st century.

The forest-water nexus in cities and human settlements

Given the role of World Cities Day in sharing innovative solutions for adaptation and mitigation, it is valuable to draw attention to the crucial, yet often overlooked, benefits of urban forests that can contribute to such solutions.

Defined by the Food and Agriculture Organization (FAO) as “networks comprising all woodlands, groups of trees, and individual trees located in urban and peri-urban areas”, urban forests include “forests, street trees, trees in parks and gardens, and trees in derelict corners”.

Urban forests provide three main advantages for cities, one of which is environmental. Their ability to absorb carbon dioxide and release oxygen, for example, contributes to the uptake of micropollutants and an improvement in air quality. According to the Environmental Protection Agency, almost 45 million tons of carbon dioxide is removed from the atmosphere every year from urban forests.

As well as the removal of carbon dioxide, urban forests also provide shade and cooling via evapotranspiration. In some circumstances, this has been seen to help lower the urban heat island effect by up to 12 degrees. Furthermore, a recent study published in 2023 by the Lancet found that increasing urban tree coverage in European cities from 15% to 30% might have prevented almost 2,600 deaths during the region's catastrophic heat wave in 2015, bringing the overall death toll down by over 40%. This is particularly relevant as the impacts of climate change worsen and the frequency and intensity of heatwaves in European countries begin to increase.

In addition to their contributions to the environment, urban forests have several economic advantages, for example by providing a cost-effective form of flood prevention. Their presence in urban environments not only makes it easier for water to penetrate the subsoil, but it also slows down the rate at which it flows through the landscape. A 2017 study conducted in Portland, United States of America, found that planting trees proved to be three to six times more effective in managing stormwater than conventional drainage systems. Their energy saving functions are also a key economic advantage, with studies showing that strategically placing trees around buildings in urban areas can lead to a decrease in the need for air conditioning by 30% and save energy used for heating by 20-50%.

Beyond these environmental and economic benefits, urban forests also play a fundamental role in promoting physical and mental welfare. In fact, the provision of green spaces for recreation and relaxation has been shown to improve the overall quality of life for individuals living in urban areas.

Urban forests are a crucial asset to sustainable development, and their provision of innovative solutions for climate adaptation and mitigation must be embraced when addressing the urban challenges of the 21^st century.