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Trees make cities cooler

From Chicago to Paris, Ottawa or Montreal, cities look for solutions to cope with hotter summers and climate change adverse effects. The solutions might be simpler than one might think.

Due to the high building density and surfaces of covered soils, cities have lost the ability to regulate temperature and, in fact, are creating heat island effects which can result in a temperature increase of up to 6°C. These extreme heat events bring many challenges to the cities: electricity grids stop working because of the heat, threatening the city energy supply; trains are not able to circulate, which can block the city food supply, and of course the population suffers from health risks associated to heat. Many cities have started looking for solutions in the most adaptive environment: nature. And, unsurprisingly, these solutions not only prove to be very efficient, they also bring many co-benefits.

After facing an extreme heatwave in 2003, the City of Paris developed a comprehensive adaptation strategy. The first objective of the strategy remains to protect Parisians in case of extreme weather events by creating emergency plans and implementing emergency measures such as opening parks 24/7 to allow access to cool spaces in the city.

Paris’ adaptation plan includes a total of 30 objectives and 35 actions. The key to the whole strategy is greening the city: Paris will plant over 20,000 trees, create parks and “cooling pathways”, and also increase urban agriculture from less than 2ha today to 33ha by 2020. These are only some examples of the many actions showing how Paris resorted to nature-based solutions to increase its resilience toward extreme weather events.

Also the Ile de France region, surrounding Paris, offers numerous examples of cities looking at nature-based solutions to cope with climate change. The City of Sarcelle created a green corridor without planting a single tree, instead letting spontaneous trees grow in order to select species adapted to the local climate, with no need for constant irrigation. In its urban planning documents, the city of Vallee de la Bievre destined a sizable area of land to provide floodway expansions in case of floods. Recent floods confirmed the efficiency of this strategy.

Canadian cities, despite their reputation for cold winters, also face hotter summers. The Canadian government conducted a research to assess how prepared cities are to face extreme heat events. They created an inventory of all the actions already in place to reduce heat island effects in major Canadian cities. Again, leaving some space to nature came as the primary solution to make the city better able to respond to extreme weather events.

There are of course some barriers for cities to implement these nature-based solutions. The Canadian research project found that, unsurprisingly, cities often claim a lack of financial resources for implementation. However, to overcome this challenge, the City of Paris issued for the first time last year climate bonds to finance some of its adaptation actions. The city managed to collect over €60mln from private funds through these bonds. In fact, examples of cities implementing nature-based solutions show that, with little investment, cities actually get multiple benefits, from mitigating the effects of climate change to increasing biodiversity, while providing more green space for citizens and eventually making the city cooler.

This blog post is based on discussions from the Resilient Cities 2016 session: “City-in-focus: Towards the implementation of a comprehensive urban cooling strategy to adapt to climate change.”