Coastal city flooding is projected to worsen in low-lying cities with climate change. Planners are concerned about the inadequacy of their current flood mitigation strategies, and the expense and risk of investing in expensive grey infrastructures, such as levees, under climate uncertainty. Implementing green stormwater infrastructure (GSI) on large privately-owned industrial land may be an attractive alternative; however, little is known about its potential for providing supplementary flood mitigation with climate change. Using Christchurch, New Zealand, as a case study, we applied hydrological modelling and spatial analysis to assess its potential to keep the impact of the increased rainfall intensities within the current flood protection capacity. Increasing groundwater levels due to rising sea levels were also considered to determine land capability for in-ground retention of stormwater. Findings demonstrate significant capability in four out of six catchments to reduce the impact of climate change–induced increased runoff volume to within the current flood protection level in the medium term (2030–2050). Two of the catchments also reduced runoff to this level in the long term (2080–2100), and under much larger storm events than the design storm, though not under all climate scenarios. Long-term flood mitigation capability can be provided where industrial land occupies a large proportion of a catchment’s area, is able to capture runoff from upstream, and where the high water table is deeper than 2 m. Industrial GSI has the potential to provide supplementary surface runoff containment through an adaptive flood mitigation planning strategy in response to unfolding climate change conditions.