Column: Sea level rise projections critical for proactive land use planning

This article is in response to recent letters to the editor and opinion pieces questioning the merits of climate science and sea level rise (SLR) projections and the need to plan for these changes. The intention is to help clear confusion and provide reliable information that can help inform local land use decision-making and adaptation planning based on science-based information, robust scientific resources and unbiased assessment of the current and predicted conditions.

The information is drawn from global and regional SLR projections based on rigorous, peer-reviewed scientific sources including, but not limited to, the United Nations Intergovernmental Panel on Climate Change (IPCC), the U.S. National Oceanographic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA) and the U.S. Geological Survey (USGS).

An important distinction is made between historical rates of SLR and projected future (accelerated) rates of SLR by sophisticated computer models. This critical difference in time frames appears to have been missed by several recent authors of letters and opinion pieces published by the Star-Advertiser. It is not accurate or appropriate to extrapolate historical SLR rates into the future for planning purposes without also accounting for accelerated rates as recommended by NOAA and others because it has been demonstrated and widely accepted in the scientific community that the historical rates are expected to rapidly increase in the future.

Sea level rise around Hawaii is projected to be greater than global mean SLR. An intermediate sea level scenario from NOAA projects a local SLR of 1.16 meters (3.8 feet) by the end of the century for Hawaii. Using the 3.2-feet Sea Level Rise Exposure Area (SLR-XA) from the 2017 State Sea Level Rise Vulnerability and Adaptation Report as a hazard overlay is a critical first step in preparing for and adapting to sea level rise impacts.

Planning decisions related to critical infrastructure with long expected life spans or low risk tolerance should consider higher scenarios. This aligns with the 2018 Honolulu’s mayoral directive No. 18-2, which requires city departments and agencies to use the 2017 Hawaii Sea Level Rise Report and the Honolulu Climate Commission’s updated sea level rise guidance of roughly 3.8 feet and up to 5.8 feet for planning, programing and capital improvement decisions for critical projects with low risk tolerance.

Sea level rise has a direct and observed impact on Hawaii’s beaches and coastal resources. Beaches exist in a delicate balance between wave energy, sand supply and water level.

From studies looking at historical shoreline locations in aerial photographs, approximately 70% of beaches in Hawaii are undergoing long-term shoreline erosion as a result of these combined processes.

This long-term change can be hard to realize due to shorter-term changes from seasonal storms and waves. In many locations, longer-term coastal erosion occurs in punctuated erosion events where the beach never fully recovers, resulting in an overall long-term landward movement of the shoreline as is currently being observed at Sunset Beach on the North Shore of Oahu.

The severe erosion hotspots on Oahu’s North Shore are just one of many examples of problem areas in Hawaii, including Poipu and Kapaa, Kauai, Northeast Oahu, and North and West Maui.

Avoiding these situations, and the cascading impacts, in the future is mutually beneficial to owners, community and decision makers, and can be achieved by using future scenarios as a planning guide.

Dolan Eversole, Brad Romine and Tara Owens are with the University of Hawaii Sea Grant College Program.