New Zealand flood maps omit coastal groundwater

New Zealand is updating its nationwide flood maps, to be released next year, to provide communities with a clearer picture of regional flood risk. However, these maps exclude the dynamics of shallow coastal aquifers, where water tables fluctuate seasonally and rise with sea levels. Research by Amandine Bosserelle and Leanne K. Morgan highlights that coastal groundwater responds to sea level rise in two ways: where the water table is free to rise, it increases groundwater flooding risk; where held down by flat topography, it weakens freshwater flow to the coast and increases saltwater intrusion. These underground changes are often omitted from adaptation planning tools, despite nearly one in five New Zealanders living in low-lying coastal areas. The omission risks giving local councils, homeowners, and insurers a false sense of security, as groundwater flooding can damage infrastructure, agricultural land, and freshwater supplies. The authors call for integrating shallow water table dynamics into national flood modelling and for coordinated monitoring efforts.