Hurricane Dorian: Harbinger of the new normal
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On September 1, 2019 destructive winds and storm surge from Hurricane Dorian devastated the Bahamas. In the days that followed, the storm weakened but expanded in size as it moved northward up the Atlantic coast of the United States. Climate change is intensifying the impacts of hurricanes like Harvey and Irma in 2017, Florence in 2018, and now Dorian in 2019, highlighting the need for coastal communities to start planning and building for what used to be the outer edge of extreme and is now becoming all too normal.
Dorian made landfall in the Bahamas as a category 5 hurricane on September 1, 2019 and then slowed to a crawl. Battered by extreme winds for over 36 hours, the Bahamas have been devastated. The world is now trying to understand the scale of the damage and loss and make sense of what it means.
A big part of what Hurricane Dorian is showing us is hurricanes have changed. Dorian is following on the heels of four incredibly devastating Atlantic hurricanes: Harvey, Irma and Michael in 2017, and Florence in 2018. Hurricane Harvey and Hurricane Florence, like Dorian, were particularly huge, slow storms that dumped massive amounts of rain.
Dorian has been particularly destructive in the Bahamas because not only was it huge and slow, it came with category 5 winds. Yet, as our post-event review of Hurricane Florence notes, the Saffir-Simpson scale, which is based on sustained wind speed, does not account for the damaging impacts of storm surge, tides, and rainfall. Indeed, because of their slow speeds, recent category 1 and category 2 storms in the United States have posed an equal if not greater risk to lives and property than higher category storms because of the intense rainfalls they have carried with them.
What does this mean for our future? Katherine Hayhoe, the Director of the Climate Science Center at Texas Tech, notes that, in thinking about hurricanes, we should be asking “how much worse did climate change make it?” Increasingly, the evidence is indicating “MUCH worse”.
Global temperatures have risen 1.4°F (0.8°C) since 1880. In response, oceans are warming. In turn, this results in stronger hurricane winds, increased rainfall, and slower-moving storms, which extends the time that people and assets are exposed to destructive winds and rains. Coupled with sea level rise, which is making hurricane storm surge worse, these changes will lead to increasingly intense, increasingly destructive hurricanes.
For example, for Hurricane Florence, sea surface temperatures were 3.6°F hotter than normal , resulting in rainfall 50% higher than it would have been without elevated air and sea surface temperatures. Sea level rise, 11 inches in North Carolina since 1950, was responsible for 11,000 (20%) of the homes impacted by Florence's storm surge. Two separate research groups found that the rainfall delivered by Hurricane Harvey, which passed over the Gulf of Mexico when sea surface temperatures were 2.7 to 7.2°F above average, was 38 percent higher than would be expected without climate change.
We are facing a new normal of hurricanes- hurricanes that are stronger, bigger, intensify faster, carry massive amounts of rainfall, and that are moving much more slowly. Recognizing this, we need to start planning and building for these types of hurricanes.
One place to start is to learn from the communities that have lived through and survived the impacts of these recent hurricanes. ISET and the Zurich Flood Resilience Alliance are doing just this. Our post-event reviews, conducted in the U.S. and around the world, identify best practices, lessons learned, and generate actionable recommendations that can help communities to build their resilience in advance of disaster for this new normal.
 Forecast: Tropical Storm Florence Discussion Number 36, NWS National Hurricane Center, https://www.climatesignals.org/node/8838
 The human influence on Hurricane Florence. Kevin Reed, Alyssa Stansfield, Michael Wehner, & Lawrence Colin M. Zarzycki, https://cpb-us-e1.wpmucdn.com/you.stonybrook.edu/dist/4/945/files/2018/09/climate_change_Florence_0911201800Z_final-262u19i.pdf
 Sea level rise responsible for 20% of the homes impacted by Hurricane Florence’s storm surge, First Street Foundation, September 2018, https://assets.floodiq.com/2018/09/28f7ba18abd9d30d0f9dc2eed82d3bad-Sea-Level-Rise-and-Hurricane-Florence-Storm-Surge-First-Street-Foundation.pdf