Adapt or mitigate: the dilemma for cities

When cities start talking about climate change resilience, it can give the mistaken impression that they have given up on trying to reduce CO₂ emissions, warns Chantal Oudkerk Pool, head of adaptation at the C40 Cities Climate Leadership Group, which brings together the mayors of more than 90 global cities. “The two disciplines of adaptation and mitigation often exist in their own silos,” she says. “It’s a missed opportunity to achieve the best outcomes.”

C40’s stated mission is to “drive urban action that reduces greenhouse gas emissions and climate risks, while increasing health, wellbeing and economic opportunities.” To help cities steer a course throughout both adaptation and mitigation, C40 contracted with WSP to develop the Adaptation and Mitigation Interaction Assessment (AMIA) software tool. “The hope is that it will provide designers and politicians with a checklist,” says Oudkerk Pool. “Have they thought about all that can be done? Have they considered all the interactions?”

The AMIA tool was guided by input from WSP staff in the UK, US, South Africa and Australia, and tested by four pilot cities: Durban, Melbourne, New York and Rio de Janeiro. It identifies four main types of interaction — two positive and two potentially negative. “First we have positive, synergistic measures, like a green roof that insulates and helps to reduce the heat-island effect. It mitigates by reducing power needed for heating and air conditioning, and adapts by reducing stormwater runoff and helping to reduce the risk of flooding. Most greening measures are synergistic in this way.”

The second positive, says Oudkerk Pool, can be achieved by “piggybacking”. “Quite often you find that a mitigating measure can be efficiently added to an adaptation measure, or vice versa. Here in the Rotterdam region, for example, a few decades ago we constructed a large, expensive storm surge barrier [the Oosterscheldekering, left]. Now tidal turbines have been added to it relatively cheaply because much of the necessary infrastructure was already there.” Or adaptation can be added to mitigation: “If you are digging up the street to put in a residual heat pipe, then why not replace the paving with permeable pavers at the same time? Again, the cost of the second action is reduced.”

“Mal-investment” is what Oudkerk Pool calls one of the less positive interactions: “Rotterdam was enthusiastic about installing charging points for electric vehicles, but some of these were in flood-prone areas. It was only at the last minute, when the adaptation people talked to the mitigation people, that the design was improved and that mal-investment was avoided.”

Finally, she says, there are interactions where trade-offs have to be made. “Most obviously, there are going to be times when air-conditioning is needed to keep people healthy and productive. Or as cities seek to become more dense to be more energy-efficient, they have to weigh that against negatives such as increasing the heat island effect, less green space, and having more economic value in a smaller area — so the impact from, say, a flood could be greater.”

In trade-off situations, it is up to each local area to carefully consider its own circumstances: “Sometimes it’s straightforward, like in Holland where, being below sea level, we either pump or drown. It’s often more nuanced than that, and what constitutes acceptable risk is a local choice.”

For this reason, and because of the considerable differences between and within cities, Oudkerk Pool is not a fan of attempting to quantify the benefits of climate risk adaptation versus mitigation. This is reflected in the tool, which flags the opportunities and risks attached but does not prescribe solutions. It does, however, contain more than 60 previously undocumented case studies from C40 cities and will be regularly updated with new ones submitted by users. “These will hopefully inspire those who design for the cities of the world and encourage those all-important conversations between adaptors and mitigators.”

Download the AMIA tool from the C40 Resource Centre

This article appeared in The Possible issue 04, as part of a longer feature about adapting to climate change