Sea-Level Rise and Tsunami Vulnerability of Habitat and Wildlife of the Northwestern Hawaiian Islands
Science Center Objects
Low-elevation Pacific islands are vulnerable to inundation from sea-level rise and sudden flooding events. The largely low-lying islands of Northwestern Hawaiian Islands (NWHI), that extend 1,930 km beyond the main Hawaiian Islands, are a World Heritage Site and part of the Papahānaumokuākea Marine National Monument. The NWHI support the largest tropical seabird rookery in the world, provide breeding habitat for 22 species of seabirds, 4 endemic land bird species and essential foraging, breeding, or haul-out habitat for other resident and migratory wildlife. High-resolution topographic data have been integrated with sea-level rise scenarios, wave models, habitat imagery, and wildlife data to better understand island and species vulnerability to inundation and respond to the need by managers to adapt future resource protection strategies to incorporate potential habitat loss and flooding.
Scenarios of global climate change predict that sea-level rise may inundate coastal and low-elevation Pacific islands. Designated as Papahānaumokuākea Marine National Monument (Monument), the Northwestern Hawaiian Islands provide habitat for the largest assemblage of tropical seabirds in the world, with >15 million birds (22 seabird species) and 4 endangered land birds found only in the Monument. Existing models of projected terrestrial and aquatic habitat changes vary greatly between islands, but even small increases in sea level may result in loss of critical habitat and increase risk of extinctions of species restricted to low-lying atolls. Current conservation strategies to address climate change are based primarily on building interconnected systems of corridors and reserves. These strategies may be inadequate for many island species that are entirely blocked from shifting their geographic ranges by anthropogenic, biological, or geographic barriers to dispersal, such as loss of habitat, urbanization, introduced predators (absent from the remote low-lying islands), or by behavioral constraints on dispersal. By identifying both the areas and species most vulnerable to sea-level rise and sudden flooding, resource managers can plan for landscape scale management and mitigation scenarios such restorations, new seabird colony establishments, or the intentional transport of species to prevent species extinction (i.e., “assisted migration” or translocation).
The Papahānaumokuākea Marine National Monument managed by National Oceanic and Atmospheric Administration, Department of Interior, Office of Hawaiian Affairs and the State of Hawaii was designated to protect the ecological integrity of the marine and terrestrial ecosystems of the U.S. Northwestern Hawaiian Islands (NWHI). High densities of tropical seabirds nest on the small islands in the chain and more than 95% of the global population Laysan (Phoebastria immutabilis) and Black-footed (P. nigripes) albatrosses nest on low-lying islands of the Monument. Endangered endemic land birds with 100% of their global population in the NWHI include Laysan duck (Anas laysanensis), Laysan finch (Telespiza cantans), Nihoa millerbird (Acrocephalus familiaris kingi), and Nihoa finch (T. ultima). The magnitude of the impact from projected sea-level rise and rapidly changing climate on seabirds and terrestrially breeding endangered species of the low-lying atolls vary by island; however the risks of inundation, habitat loss and new diseases are great. Measures of exposure and sensitivity of fauna and flora are needed to help managers prioritize and coordinate their management decisions in accordance to vulnerability at the landscape and global scale.
This project seeks to reduce uncertainty for land managers by using models of sea-level rise, wave driven storm surge, and wildlife population vulnerability, distribution and abundance data to provide information needed for multi-dimensional decision making across this landscape in the face of climate change.
Highlights and Key Findings:
Using remote sensing and geospatial techniques, we estimated topography, classified vegetation, modeled sea-level rise (SLR) and evaluated vulnerability of bird species. On the basis of high-resolution airborne data collected during 2010−11 (root-mean-squared error = 0.05–0.18 m), we estimated the maximum elevation of 20 individual islands extending from Kure Atoll to French Frigate Shoals (range: 1.8–39.7 m) and computed the mean elevation (1.7 m, standard deviation 1.1 m) across all low-lying islands. Our models of passive SLR (excluding wave-driven effects, erosion, and accretion) showed that approximately 4 percent of the total land area in the NWHI will be lost with scenarios of +1.0 m of SLR and 26 percent will be lost with +2.0 m of SLR. Some atolls are especially vulnerable to SLR. For example, at Pearl and Hermes Atoll our analysis indicated substantial habitat losses with 43% of the land area inundated at +1.0 m SLR and 92% inundated at +2.0 m SLR. Across the NWHI, seven islands will be completely submerged with +2.0 m SLR.
The limited global ranges of some tropical nesting birds make them particularly vulnerable to climate change impacts in the NWHI. Climate change scenarios and potential SLR impacts emphasize the need for early climate change adaptation and mitigation planning, especially for species with limited breeding distributions and/or ranges restricted primarily to the low-lying NWHI such as: Black-footed Albatross (Phoebastria nigripes), Laysan Albatross (P. immutabilis), Bonin Petrel (Pterodroma hypoleuca), Gray-backed Tern (Onychoprion lunatus), Laysan Teal (Anas laysanensis), Laysan Finch (Telespiza cantans), and Hawaiian monk seal (Monachus schauinslandi). Furthermore, SLR scenarios that include the effects of wave dynamics and groundwater rise may indicate amplified vulnerability to climate change driven habitat loss on low-lying islands.