Flooding is going to happen more often in Hawaii as sea level rises

The big waves seen in recent viral videos weren’t necessarily caused by the climate crisis — but as the seas rise, Hawaii can expect to see a lot more coastal flooding

Ethan Freedman
Climate Reporter, New York
Monday 18 July 2022 21:51 BST
Huge waves crash into wedding reception in Hawaii after tropical storm

Video of some massive waves hitting Hawaii’s Big Island have made the rounds on social media early this week — especially one that seemed to nearly ruin a wedding reception, sending guests running for higher ground.

The waves were caused by an unusually high surf swell to the south of the islands, according to the National Weather Service (NWS), pushing waves pretty high.

These kinds of surf swells happen in Hawaii, and big waves can hit coastal spots regularly — that’s just part of living in the middle of the Pacific Ocean, unrelated to the global climate crisis.

As warmer temperatures raise the world’s oceans, the islands are also sinking closer and closer to the water – and many coastal areas are becoming more at risk of flooding.

Two videos showed waves crashing on the Big Island’s southwest coast. One hit the aforementioned wedding event, while the other pushed waves high enough to reach over a two-story building, reports AccuWeather.

By 2150, sea levels along that shoreline will rise by at least 2.7 feet (0.8 metres), according to Nasa — but that’s under the lowest possible emissions scenario. With more emissions, sea level could rise by 4 ft (1.2 m) or, in something of a worst-case scenario, 8 ft (2.5 m).

Those shifts will likely put much of the Hawaiian coast at risk of increased flooding.

With 3.2 ft of sea level rise, both the spot where waves crashed over the two-story building and the wedding reception would fall in the coastal flood hazard zone — meaning a 1 per cent annual chance of flood, according to an analysis from the state of Hawaii and other groups.

Notably, the Big Island’s southwest coast isn’t where the state expects to see the most damage from sea level rise. Over on Oahu, the state’s biggest city of Honolulu sits along a low-lying stretch of that island’s southern coast.

According to the state’s analysis, with 3.2 ft of sea level rise, vast swaths of Honolulu are going to sit in the coastal flood hazard zone — with many low-lying areas flooding annually when big waves hit.

Sea level rise would also lead to inland flooding as ocean water pushes up and in and regular tidal flooding, the state notes. And it’s already happening – water levels in Hilo, on the Big Island, are now rising by one inch every four years, they add.

Across the state, 3.2 feet of sea level rise would make over 25,000 acres — 60 per cent the size of Washington, DC — unusable, a state report concludes. About a third of that of land is in urban areas, with 25 per cent in agricultural areas.

Around 20,000 people will need new homes, the state report notes, and many of the island chain’s iconic beaches could erode. This is also just what would happen if there was 3.2 feet of sea level rise; if waters were to go further, the damage would likely spread.

In addition to coastal flooding and erosion, the climate crisis will likely bring threats such as ocean acidification and coral bleaching to Hawaii, notes the US Environmental Protection Agency.

These kinds of issues are not unique to Hawaii either. Places like the Maldives, an archipelagic nation in the Indian Ocean, are facing immense losses of land as sea level rise eats up their low-lying coasts.

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