Is Hawaii going to be underwater? While the entire Hawaiian archipelago is not predicted to vanish completely, the islands face significant challenges from rising sea levels. This phenomenon will impact Hawaii’s coastlines, infrastructure, and natural environment. This article explores the scientific realities of sea level rise and its potential consequences for the Hawaiian Islands.
Understanding Sea Level Rise
Global sea level rise stems from two main factors: thermal expansion of ocean water and the melting of glaciers and ice sheets. As the ocean warms, its water expands, contributing to global sea levels. Additionally, melting ice from glaciers and vast ice sheets, particularly in Greenland and Antarctica, adds water to the oceans, elevating sea levels.
While these are global drivers, local sea level rise in Hawaii is influenced by additional factors. Ocean currents and local geological processes, such as land subsidence or uplift, can modify the rate at which sea level changes relative to the land. Long-term observational data from local tide gauge stations confirm sea level is rising around Hawaii. Models indicate Hawaii and other tropical Pacific sites may experience sea level rise 16% to 20% higher than the global average.
Hawaii has seen sea levels rise by about 5 inches since 1970, with some areas like Hilo Bay experiencing a 10-inch rise since 1950. Projections suggest Hawaii could experience 8 inches of sea level rise by 2050 under an intermediate scenario, and up to 3.5 feet by 2100. Recent scientific literature indicates that 3 to 4 feet of sea level rise by 2100 is now considered a mid-range scenario for Hawaii. Sea level is committed to rise for centuries beyond 2100.
How Rising Waters Affect Hawaii
Rising sea levels pose multiple threats to Hawaii’s environment and infrastructure. Coastal erosion is a significant concern, directly threatening beaches, homes, and roads. Estimates suggest 70% of Hawaii’s beaches are threatened by erosion, with some Oahu areas having lost nearly 30% of their sandy shoreline due to erosion and shoreline hardening.
Saltwater intrusion into freshwater aquifers presents a challenge to Hawaii’s drinking water supplies. The islands source 99% of their domestic water from groundwater, which exists as freshwater lenses floating on saltwater. As sea levels rise, the interface between freshwater and saltwater shifts, allowing seawater to contaminate these underground reserves. This intrusion is further exacerbated by over-pumping of aquifers, which can draw saltwater inland.
Increased coastal flooding already impacts communities, tourism infrastructure, and cultural sites. By 2050, Hawaii could experience 150 high tide flood days per year in some locations, with formerly dry beaches becoming chronically underwater. This chronic flooding is projected to render over 25,800 acres of land unusable statewide and put approximately 6,500 structures at risk. Nearly 550 cultural sites and 38 miles of major roads could also be exposed to chronic flooding.
Natural ecosystems also face consequences, including coral reefs and low-lying wetlands. Sea level rise can disrupt coastal wetlands, endangering habitats and reducing their ability to buffer against storms. Coral reefs, which provide shoreline protection and are culturally significant, are at risk from inundation and degraded water quality.
Hawaii’s Response and Adaptation
Hawaii is implementing various strategies to adapt to rising sea levels. Adaptation measures often fall into categories such as protection, accommodation, and retreat. Nature-based solutions, including reef restoration and dune reconstruction, utilize natural systems to protect coastlines. These “green-blue” approaches offer co-benefits like increased carbon storage and habitat preservation, often proving more effective and sustainable than traditional engineered solutions like concrete seawalls.
Engineered solutions, such as seawalls, have historically been used for coastal protection, but they can exacerbate beach loss and erosion. Land-use planning strategies emphasize discouraging hard infrastructure and encouraging development further inland. Hawaii’s Coastal Zone Management Act discourages seawall construction and designates shoreline setback lines.
Managed retreat, the relocation of development away from vulnerable coastal areas, is another adaptation strategy. While challenging due to community acceptance and funding issues, managed retreat can restore beaches and dunes, improve shoreline public access, and support Hawaiian cultural practices. The proposed $60 million managed retreat revolving fund in Maui County illustrates efforts to finance such transitions. State agencies are also working to identify vulnerable facilities and assess mitigation options.
Community-led initiatives and governmental policies are integral to building resilience across the islands. The Hawaii Climate Change Mitigation and Adaptation Commission, established in 2017, develops vulnerability and adaptation reports and leads the state’s efforts to address climate change impacts. Local governments also develop hazard mitigation plans that incorporate sea level rise and coastal erosion.
Reframing the ‘Underwater’ Question
The question of whether Hawaii will be “underwater” requires a nuanced understanding. While the entire Hawaiian archipelago is not projected to be completely submerged, significant low-lying coastal areas are vulnerable to inundation and increased flooding. The term “underwater” signifies ongoing land loss, infrastructure damage, and profound landscape changes, rather than a sudden, complete disappearance.
Previously dry areas could become chronically flooded, transforming coastal communities and natural habitats. This includes the loss of beaches, homes, and infrastructure, impacting the economy, water supply, and cultural heritage. The focus is on adapting to these progressive changes and mitigating their effects. Scientific monitoring and ongoing efforts address these challenges.