Every day, people around the world move from rural areas to the city in search of work and a better life. Cities offer unique opportunities, but risks as well. In hot countries, these include the deadly threats of urban heat and air pollution.

High rise buildings and paved roads trap heat, raising temperatures and creating urban heat islands. These heat islands don’t just threaten people’s health – they encourage people to use energy-intensive air conditioning, potentially driving more global warming. Clever planning can help cool our cities and clean our air. And bodies of water – from rivers and canals to urban mangroves – have a big role to play. Here’s why.

Floating wetlands and freshwater mangroves

Firstly, bodies of water absorb heat. But they also support another great cooling solution – greenery. Trees, bushes and plants cool the air by giving shade and absorb and reflecting heat.

In Singapore the Punggol Waterway project, which opened to the public in 2011, has created an artificial river at the heart of a large residential development. The waterway features ‘floating wetlands’ – interlocking hexagons planted with a range of wetland species. And the banks of the waterway are lined with freshwater mangroves, adding more vegetation to the community.

Medellin, once the world’s most dangerous city, has over 30 Green Corridors that heal and cool. Lining the cities roads and waterways are vast planting projects providing shade and cleaning the air in residential areas. Streams and waterways connect three of the main hills in the city, providing the irrigation that keeps Medellin green.

Medellin's urban greening programme is transforming the city

With cities swelling and temperatures rising, the world urgently needs more urban cooling solutions. That’s why this year’s Ashden Awards feature an urban cooling Award, sponsored by Climateworks K-CEP, for the very first time. The Punggol and Medellin schemes are on the longlist, along with a landscaping for urban spaces and high-rises project run by Singapore’s urban redevelopment authority, and a public space greening programme in the Ethiopian capital Addis Ababa.

Sustainable transport

Waterways can tackle a host of urban sustainability challenges beyond dangerous heat. One is air pollution, which causes 1 in 9 deaths worldwide. Fumes from cars and other vehicles are a major factor, and residents of our crowded cities are most at risk.

Waterways support vegetation that cleans the air – but they are also an ideal place for planners to introduce new footpaths and bike tracks, helping people swap polluting cars for cleaner transport. Paths and cycle lanes run alongside Medellin’s waterways – while the Punggol development includes a 9km coastal promenade, as well as generous walking space along the side of the waterway itself.

We look forward to announcing our first urban cooling winner at the 2019 Ashden Awards on July 3. Forwards-thinking innovators, like those on our longlist, can help turn a trickle of bright ideas into a flood.