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October 17, 2018Sea level rise observed since 1970 responsible for 43% of homes impacted by Hurricane Irma’s storm surge

(NEW YORK, N.Y.) Data scientists from the non-profit First Street Foundation in collaboration with Dr. Jeremy Porter, a professor at Columbia University, have found that sea level rise since 1970 caused an additional 57,000 homes to be impacted by Hurricane Irma’s storm surge.

With Hurricane Michael’s devastating impact along Florida’s panhandle still being quantified, First Street Foundation wanted to understand the role sea level rise played in similar, more documented events like Hurricane Irma. In 2017, Hurricane Irma’s storm surge impacted over 133,000 homes across Florida, causing extensive flooding and damage. The research used a geospatial analysis to model the impact of an Irma-like storm at the sea levels observed in 1970, and found that ~57,000 of the properties impacted last year would not have been affected with 1970 sea levels – signaling that the rise in sea level was responsible for these additional impacts.

The study also found that if Hurricane Irma were to hit at the sea level projected for 2050 by the Army Corps of Engineers, approximately 15 inches above current levels, the storm surge would affect an additional 200,000 homes. In other words, a 1.26 foot increase in nearby sea levels alone would result in a 150% increase in the number of homes impacted by Hurricane Irma’s storm surge.

“Similarly to what was found with our analysis of Hurricane Florence in the Carolinas, we know that sea level rise made the damage from Hurricane Irma significantly worse,” said First Street Foundation’s Head of Data Science Steven McAlpine.

According to tidal data in the region, relative sea level off the coast of Florida has risen approximately 7 inches since 1970. Higher sea levels cause greater storm surge, as there is more water available for hurricanes to push onto land, and that additional water removes friction that would otherwise slow the surge. Research has shown that sea level rise has a non-linear positive impact on storm surge; the conservative models used in this research show that increases in sea level rise result in an additional 23% relative increase in storm surge.

“Small increases in sea levels are causing disproportionate increases to the reach of storm surge.” said Dr. Jeremy Porter, “This is especially true in Florida because of the low-lying topography.”

In addition to sea level rise, the scientists found that changes in housing development patterns also played a significant role in the number of homes affected by Hurricane Irma’s storm surge. Since the 1970’s, much of the region’s wetlands and conserved areas have been developed for urban use. Many of the homes built in these areas were impacted by Hurricane Irma’s storm surge. By applying Hurricane Irma’s observed storm surge to the housing development patterns of 1970, the scientists found that only 72,000 homes would have been impacted, compared to the 133,000 impacted in 2017. In other words, 61,000 homes in the impacted surge area were developed since 1970.

“Recent hurricanes such as Hurricane Irma, Florence and now Michael, are demonstrating how sea level rise has a dramatic impact on the number of homes affected by hurricane storm surge. As sea levels and coastal development continue to rise, this will only get worse,” said Matthew Eby, Executive Director of First Street Foundation. “The time to rethink America’s sea level rise and adaptation strategy is now.”

First Street Foundation is a 501(c)(3) tech nonprofit that educates policymakers and the public about the risks, causes, and solutions to sea level rise.

Methodology behind this research can be found here. For questions please reach out to pr@firststreet.org.

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Sea Level Rise Worsens Storm Surge

1970Hurricane Irma Scenario

2017 Hurricane Irma

2050 Hurricane Irma Scenario

1970 sea levelModeled storm surge: 3.1 ft

Sea level increase: +0.6 ftObserved storm surge: 3.9 ft

Sea level increase: +1.8 ftModeled storm surge: 5.4 ft

Analysis Example: Hurricane Irma’s Impact on Miami

1970: Hurricane Irma Scenario

2017:Hurricane Irma

2050: Hurricane Irma Scenario

Hurricane Irma’s Total Storm Surge Impact: Miami, Marco Island, and Key West

333,000HOMES

133,000 HOMES

76,000HOMES

Residential development numbers held constant for all three scenarios

Hurricane Irma Scenarios combined: 1970, 2017, and 2050

Miami location

1970

2017

2050Miami, FL

1970Hurricane Irma Scenario

Marco Island Location

2017Hurricane Irma

2050 Hurricane Irma Scenario

Hurricane Irma Scenarios combined: 1970, 2017, and 2050

1970 sea levelModeled storm surge: 5.8 ft

Sea level increase: +0.6 ftObserved storm surge: 6.5 ft

Sea level increase: +1.8 ftModeled storm surge: 8 ft

Analysis Example: Hurricane Irma’s Impact on Marco Island

Marco Island, FL

1970

2017

2050

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Sea Level Rise Worsens Storm Surge

1970Hurricane Irma Scenario

Key West Location

2017Hurricane Irma

2050 Hurricane Irma Scenario

Hurricane Irma Scenarios combined: 1970, 2017, and 2050

1970 sea levelModeled storm surge: 2.2 ft

Sea level increase: +0.6 ftObserved storm surge: 2.9 ft

Sea level increase: +1.8 ftModeled storm surge: 4.5 ft

Analysis Example: Hurricane Irma’s Impact on Key West

1970

2017

2050

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Sea Level Rise Worsens Storm Surge

Key West, FL

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Sea Level Rise Worsens Storm Surge

Top 15 Impacted County

Housing Units Impacted by Irma / Irma-like storm

1970 Surge Level 2017 Surge Level 2050 Surge LevelMiami-Dade 19,000 45,000 136,000Monroe 20,000 24,000 27,000St. Johns 4,000 7,000 23,000Lee 2,000 6,000 21,000Volusia 6,000 9,000 17,000Broward 1,000 3,000 17,000Collier 3,000 7,000 17,000Charlotte 2,000 4,000 15,000Duval 8,000 10,000 15,000Brevard 3,000 5,000 14,000Flagler 3,000 3,000 6,000Clay 2,000 2,000 4,000Sarasota 0 1,000 4,000Putnam 1,000 1,000 2,000Nassau 1,000 1,000 2,000

Values rounded to nearest 1000