Rising Sea Level
WHAT’S HAPPENING NOW?
The ice caps are melting, sea levels are already rising, and Hawai‘i is feeling the impacts. The sea level around Hilo Bay has risen by 10 inches since 1950. And now, it’s rising faster at about 1 inch every 4 years. This increases the frequency and reach of coastal floods, which affect our communities. 2017 was a record flood year for Honolulu (37 flood days, when historically, the average has been around 4 days). These floods were fully attributed to climate change/sea level rise. Today, Hawai‘i has 66,000 people regularly at risk from coastal flooding. In Kailua for example, 50% of the population is locked-in below expected flood zones.
Maps of historic coastal erosion can be found on the Hawaiʻi Climate Data Portal’s Coastal Erosion tool.
What does this mean for Hawai‘i?
MORE COASTAL EROSION. 13 miles of beaches around the state are already gone, including 10% of O‘ahu’s beaches because of coastal erosion. 70% of beaches around the state are currently threatened.
INCREASED INLAND FLOODING. Since the 1960s, the number of annual flood days in the State has increased significantly. Our communities are at risk, and not just near the coast. Flooding is worsening further and further inland where seawater will flow backwards through storm drains, and upwards by coastal groundwater emergence – leading to pools of dirty, contaminated, brackish water where we live. In Mapunapuna industrial area on O‘ahu, the last decade has seen a dramatic increase in the number of flood days, so much so that the area is now considered to be in a state of chronic flooding. This hurts businesses, damages vehicles and infrastructure, and damages our coastal ecosystem. The impacts of sea level rise are further exacerbated in areas that were historically wetlands such as in Mapunapuna and other areas like Waikiki and the Keehi interchange. As the infill settles land sinks making it more prone to flooding.
MORE FREQUENT HIGH TIDE FLOODING IS THREATENING OUR CITIES. The frequency of yearly floods in Honolulu has spiked, and you don’t have to live on the coast to see the evidence. More flooding means increased damage to roads and buildings and overwhelmed drainage systems. In Hawai‘i, where we often have only one road in and out of our communities, road closures because of flooding and erosion are a big problem.
TRADITIONAL AND CULTURAL PRACTICIES ARE AFFECTED. Sea level rise affects traditional and customary practices, including fishpond maintenance, cultivation of salt, and gathering from the nearshore fisheries. This can have a negative effect on people’s spiritual and mental health.
WHAT’S COMING?
As global warming continues, sea level rise will accelerate. Hawaiʻi’s coastal areas will see rapid increases in tidal flooding events beginning in the mid-2030s. Honolulu will likely experience a level of sea level rise between 1.3 feet and 5.8 feet by the end of the century depending on future carbon emissions, making it one of the most vulnerable urban areas in the United States. 3.2 feet of sea level rise would lead to chronic flooding of 9,400 acres of land, displace over 13,000 residents, and flood 17.7 miles of roads, threatening access to numerous coastal communities.
Chronic flooding will lead to an additional 25,800 acres of land becoming unusable, and 6,500 structures are projected to be at risk due to sea level rise. About 550 cultural sites, 38 miles of major roads, and at least $19 billion in assets will be vulnerable to chronic flooding. Sea level rise is particularly threatening to Waikīkī and military infrastructure around Pearl Harbor. Sea level rise is an existential threat to Hawaiʻi’s food security, water supply, economy, cultural heritage, and overall habitability.
Statewide efforts at mitigation and adaptation are necessary in the face of rising sea levels. This includes changes to building design, community relocation, permitting changes, and protection of coastal environments. To see how your community will be impacted in different sea level rise situations, we encourage you to use the Hawaiʻi Climate Data Portal’s sea level rise visualization tool.