Researchers from CIÊNCIAS show that green solutions can reduce urban heat stress

Researchers from the Centre for Ecology, Evolution and Environmental Change (CE3C) at the Faculty of Sciences of the University of Lisbon (ULisboa Sciences) co-led an international study, recently published in the journal Landscape and Urban Planning, which analyses the impact of urban planning solutions on reducing heat stress in cities. The study focuses on the Lisbon Metropolitan Area, which is home to 27% of Portugal’s population, and on Islamabad (Pakistan), highlighting both the potential and the limitations of so-called nature-based solutions.

The study, which involved researchers from CE3C Tiago Capela Lourenço and Inês Gomes Marques, demonstrates that interventions such as the expansion of green spaces, tree plantation and the removal of impervious surfaces can significantly reduce heat stress on urban populations, in some cases reducing their exposure by up to 40% fewer days of extreme heat. These effects are primarily due to the creation of shade and the reduction in the temperature of urban surfaces. The results also show that different strategies have different impacts:

• During the day: Trees are particularly effective at reducing daytime temperatures when they are found in large, continuous areas (by up to around 0.5°C);

• At night: Removing impervious surfaces (such as concrete and asphalt) has the greatest impact on reducing night-time temperatures. This measure reduces the number of days with heat stress by between 10% and 20%, benefiting a greater number of people and playing a crucial role in curbing the loss of sleep associated with heatwaves;

• The benefits tend to be localised, diminishing rapidly outside the areas where the intervention has taken place.

These strategies were not merely theoretical; the solutions were co-created over a three-year period with a diverse group of stakeholders. The process involved representatives from the 18 municipalities of the Lisbon Metropolitan Area, experts in the field of climate governance, and academics, underscoring the importance of participatory approaches to ensure effectiveness and social acceptance.

Despite the positive results, researchers warn of a critical issue: nature-based solutions alone are not enough to offset the future impacts of climate change, particularly given current policies. In other words, although essential, these measures only partially mitigate the projected increase in urban heat.

The findings have direct implications for public policy, indicating that:

• Interventions should be prioritised in densely populated areas;

• Urban planning should strategically incorporate green and blue solutions;

Adapting to urban heat requires a combined approach involving planning, climate policy and social justice, given the greater impact on vulnerable populations.

In this context, adaptation is essential to prevent the direct and indirect impacts of climate change in the short term. The CE3C team at the Faculty of Sciences of the University of Lisbon, led by Tiago Capela Lourenço, is currently taking part in a European project called AdaptationHubs. This project supports the creation of an Adaptation Hub in Portugal, that is, a coordination platform which aims, within the framework of the European Union’s Mission on Climate Change Adaptation, to increase the resilience of Member States, improve coordination, promote the sharing of solutions and strengthen climate risk management at national and local level.

Improving urban heat adaptation is therefore a crucial step towards building cities that are more resilient, sustainable and better prepared for future climate challenges.