Spatiotemporal economic risk of national road networks to episodic coastal flooding and sea level rise

This study delivers a spatiotemporal economic risk evaluation of New Zealand’s road network to extreme sea-level driven flooding and relative sea level (RSL) change from 2020 to 2120. A spatial risk analysis framework was developed to calculate direct monetary loss as the expected exceedance probability loss (EPL) and average annual loss (AAL) at the road component level. These risk metrics were estimated at national and regional levels between 2020 and 2120 using RSL projections for medium confidence Shared Socio-economic Pathways (SSP) and local vertical land motion (VLM). New Zealand’s direct economic risk was primarily driven by direct damage to local access, collector, and arterial roads. At national levels, expected road AAL at 2100 could occur 10 to 20 years earlier as downward VLM accelerates local RSL rise later this century. Regional VLM trajectories may cause expected AAL to occur 20 years earlier from downward land motion and 5 years later from upward motion. This signals a need for VLM inclusion in future economic risk evaluations of episodic coastal flooding at all spatial and temporal scales. The spatiotemporal model approach has future potential for road network risk hotspot identification and structural or non-structural adaptation intervention evaluation under future RSL change.