Rising sea levels caused by climate change are bringing an often-overlooked threat to coastal communities rising groundwater. While coastal erosion and storm surges have been widely studied, the inland spread of flood hazards due to groundwater rise remains a hidden danger. A recent study by Cox et al. focuses on Dunedin, New Zealand, a city already facing periodic flooding, and presents a method to predict how rising seas will impact groundwater levels, offering crucial insights for flood risk management.
The research, based on data from 2019 to 2023 collected from 35 groundwater sensors, shows that as sea levels rise, groundwater levels will also increase, limiting the land’s ability to absorb rainfall and leading to higher risks of surface flooding.
Even before reaching the surface, groundwater rise can infiltrate basements, destabilize building foundations, and overwhelm wastewater systems, creating serious infrastructure problems. Over time, groundwater may emerge as springs, causing flooding in areas much farther inland than previously expected.
Dunedin’s case study highlights a widespread challenge that many low-lying coastal cities could soon face. Unlike coastal flooding, which can be mitigated with seawalls or dunes, groundwater rise bypasses these barriers, making it harder to control. The researchers acknowledge certain uncertainties in their predictions, but their method offers a practical and cost-effective way for cities worldwide to assess hidden flood risks. Recognizing groundwater rise as an early warning signal allows urban planners to take proactive steps to adapt infrastructure and protect communities from future flooding.