Challenge
Medellín, Colombia’s second-largest city, sits in a narrow Andean valley where rapid urban growth, vehicle traffic and limited green space combine to create intense urban heat. Annual temperatures have been rising, increasing heat stress for residents — particularly in dense, low-income neighbourhoods. The city also faces flash flooding during heavy rain events, aggravated by impervious surfaces.
The Green Corridors Programme
Between 2016 and 2019, Medellín converted 30 heavily trafficked streets into “green corridors” (Corredores Verdes). Each corridor features dense planting of native trees and shrubs along the central reservation and footpaths, combined with cycling infrastructure, wider footways and improved drainage.
What Was Built
- 36 km of corridors across 30 streets in the city centre and El Poblado
- 880,000 plants installed including trees, shrubs and ground cover species
- Drip irrigation powered by water harvested from the roadway
- Cycling and pedestrian priority lanes reducing private vehicle space
Measured Cooling Effect
Thermal monitoring conducted before and after the corridors found peak surface temperatures fell by 2–3 °C along greened streets compared with control streets. The European Environment Agency’s UHI mapping tool was used to validate the city-scale thermal improvement.
The corridors also improved air quality (PM₁₀ concentrations fell by up to 14% in adjacent areas) and reduced surface runoff through soil infiltration.
Outcomes
The transformation was rapid and visible. Within one year of completion, the corridors became popular social spaces as well as functional climate infrastructure. UN-Habitat cited Medellín as a global model for nature-based urban cooling.
- Temperature reductions of 2–3°C on greened streets
- 30 corridors covering 36 km across the city
- Air quality improvements of up to 14% in PM₁₀
- Awarded UN-Habitat Scroll of Honour 2019
Lessons Learned
- Street redesign and greening can be delivered at scale quickly when political will exists
- Native species adapted to local conditions require less irrigation and maintenance
- Combining green infrastructure with cycling and pedestrian improvements multiplies social benefits
- Real-time thermal monitoring builds the evidence base for scaling up
Tools Used in This Case Study
Climate Tools Applied
