Garibaldi Street, Lyon

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Garibaldi Phase 1: first growing season (Summer 2015). Image credit: Laurence Daniere

Results have indeed been very conclusive. The increased presence of trees and other vegetation along the refurbished sections of Garibaldi Street has been shown to lower ambient temperatures in August 2016 and August 2017 by 1.78C and 2.33C on average, and thermal comfort by 9C (Universal Thermal Climate Index). Further measures conducted in 2019 were able to isolate the impact of irrigation over the cooling effect generated by vegetation, highlighting this was responsible for between 0.5C to 1C in the observed temperature reduction.

Repurposing the underpass as a stormwater collection tank proved costly and awkward to manage in the long run – it collects more water than what the project needs, and due to its size, is managed by a separate entity, responsible for major drainage infrastructure across the Greater Lyon area. This has made getting access to the water collected for irrigation somewhat cumbersome, due to a complex authorisation process. As a result, for future projects, it is anticipated that smaller, purpose-built tanks that can be assimilated to “irrigation systems” will be preferred (although they do also contribute to sustainable drainage), to allow for a more cost-effective and less time-consuming set-up and operations.