The Colombian city of Medellín has emerged as a global example of climate adaptation after planting approximately 880,000 trees and more than 2.5 million shrubs and other plants under its Green Corridors programme, significantly reducing urban temperatures and improving environmental quality.
Launched in 2016, the initiative transformed roadsides, parks, riverbanks and public spaces into interconnected green corridors to combat the city’s growing urban heat island effect. Medellín, located in the Aburrá Valley, had experienced rising temperatures as rapid urbanisation replaced vegetation with buildings, roads and paved surfaces that absorb and retain heat.
According to scientific assessments, the large-scale greening programme reduced average air temperatures across the city by around 2°C, while heavily shaded areas recorded localised cooling of up to 5°C. The cooling effect is achieved through tree shade, which blocks direct sunlight from heating urban surfaces, and evapotranspiration, a natural process in which trees release water vapour that cools the surrounding air.
In addition to lowering temperatures, the Green Corridors programme has improved air quality by trapping airborne pollutants and absorbing carbon dioxide. The expanded vegetation has also created habitats for birds, butterflies, bees and other pollinators, contributing to increased urban biodiversity.
The greener public spaces have encouraged walking and cycling by making streets more comfortable for residents while providing healthier recreational areas. The project also generated thousands of jobs related to landscaping, maintenance and urban greening, strengthening community participation in environmental conservation.
Experts have cautioned against viral claims that Medellín cooled by 10°C after planting trees. Current scientific evidence indicates that while surface temperatures beneath tree cover can differ substantially from exposed asphalt, measured reductions in air temperature average about 2°C across the city, with cooling reaching up to 5°C in some shaded locations.
The Green Corridors programme has received international recognition from organisations including the World Resources Institute, C40 Cities and the Inter-American Development Bank as a successful example of nature based climate adaptation.
Urban planners say Medellín demonstrates how integrating extensive tree planting with long term maintenance and thoughtful city planning can improve climate resilience, public health and overall quality of life while helping cities adapt to rising temperatures.