PNNL

The Science
Future storm surges will be amplified by sea-level rise, but the spatial variability of this amplification has not been systematically addressed, in part due to nonlinear interactions that take place in different parts of a hurricane track. In this study, scientists from the Department of Energy’s Pacific Northwest National Laboratory evaluated the nonlinear response of storm surge to sea-level rise using a high-resolution model of Hurricane Katrina under five different sea-level rise scenarios. They found that storm surge heights in the lower floodplain region can increase more than twice as much as sea-level rise as a result of nonlinear amplification effects. 

The Impact
Hurricane-driven storm surges are among the most damaging and costliest natural disasters, so it is critical to understand how sea-level rise may be influencing storm surges. This study identified specific portions of coastal topography that may experience increases in storm surges that are even larger than the rate of sea-level rise, which is valuable for assessing coastal infrastructure resilience. The study also highlights the need for dynamic modeling in order to account for complex interactions associated with coastal storm surge in the context of long-term sea-level rise. 

Summary
The study team used the unstructured-grid, finite-volume, coastal ocean model known as FVCOM (Finite-Volume Coastal Ocean Model) to simulate the effect of Hurricane Katrina on the Gulf Coast under five different scenarios of sea-level rise, ranging from 0 to 2.0 meters. The model was driven by the observed Katrina wind field, and includes a wetting and drying process to accurately simulate storm surge heights across complex coastal topographies. To assess the nonlinear interaction between surge height and sea-level rise, the team looked at three different regions across the land-ocean boundary near the hurricane track: the offshore coastal area, the upper floodplain, and the lower floodplain. Although maximum storm surge height increased with sea-level rise in all three regions, the response under larger sea-level rise scenarios was muted in the upper floodplain and exacerbated in the lower floodplain. These results highlight the need for additional research with dynamic, high-resolution models to better understand the interactions between sea-level rise and storm surge in different regions, for different storm patterns, and under different sea-level rise scenarios. 

PI Contact
Ian Kraucunas, Pacific Northwest National Laboratory, Ian.Kraucunas@pnnl.gov 
Zhaoqing Yang, Pacific Northwest National Laboratory, Zhaoqing.Yang@pnnl.gov 

Funding
This study was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, as part of the Regional Integrated Assessment Modeling Project under the Multisector Dynamics research program.