Bucket up! Can large private properties provide substantial coastal flood mitigation under climate change?

Abstract

Protecting vulnerable coastal cities from flooding under climate change is challenging. Many studies have demonstrated that conventional approaches, like the installation or reinforcement of front-line defence structures (e.g., walls and dykes), will be inadequate, and there is a risk of under or over investment under climate change uncertainty. An alternative is to provide additional green stormwater infrastructure facilities, or ‘buckets,’ for holding the additional surface water. However public land capable of serving as such is often missing. While many cities are now requiring private landowners to install small buckets on their land, regardless of their capability for mitigating flooding, their impact may be minor as implementation is too slow. We need a more cost effective and strategic approach for installing larger buckets to ensure our communities and central business districts are protected. Can private properties with large areas of open space, like industrial lands, provide a better solution? Here, we apply a hydrological and spatial analysis methodology to assess the potential of large industrial parcels across catchments in Christchurch, New Zealand, to provide substantial flood mitigation under different climate change projections. We find industrial parcels could provide substantial flood mitigation within three of six study catchments, reducing the severity of climate change-induced increased runoff volume to the current flood protection level under any climate scenario in the immediate future (2030-2050). Industrial land in two of these catchments could also reduce runoff to this level in the distant future (2080-2100), and under larger storm events, though not under all climate scenarios.