Exposure to shallow groundwater in New Zealand's coastal lowlands: what is exposed and why does it matter?

Climate change is a global challenge for humanity, with sea-level rise and associated groundwater rise posing particular threats to coastal communities. Climate-change-driven sea-level rise is causing groundwater levels to rise in New Zealand’s coastal lowlands (10 meter above current sea level), creating a largely overlooked but significant slow-onset hazard. Progressively shallower groundwater can damage buildings, roads, and underground infrastructure through waterlogging, buoyancy, cracking, and accelerated material degradation. This research uses newly developed national groundwater models and the RiskScape hazard-exposure framework, to estimate building, road, and people exposure to shallow groundwater (within one metre of the surface). Nationally, between 0.5 and 1.7 million buildings, between 7,870 and 35,961 km of roads, and up to 1–3 million population may already be exposed to shallow groundwater. In the coastal lowlands, 83, 548 − 286,859 buildings, 1,368-5,271 km of roads, and between 0.2 and 0.7 million people may already be exposed. Exposure is highest in regions as Canterbury, Auckland, and Waikato, and essential services – including clinics, schools, and lifeline utilities – are also at risk. As New Zealand’s largest city, the Auckland region has the highest estimated replacement cost of buildings and roads exposed to shallow groundwater. Canterbury, and the Bay of Plenty also remain the most highly exposed regions in terms of buildings, roads, and population. This research represents New Zealand’s first essential step towards a national risk assessment of built assets to shallow groundwater by quantifying the baseline exposure today. This baseline underscores the need for future work on vulnerability, damage thresholds, and adaptation strategies.