Hurricanes cause approximately $28 billion in damages to the United States economy per year, according to government estimates. In addition, the U.S. government expects to pay about $18 billion per year in hurricane relief and recovery.
In other words, hurricanes are well worth their definition as “natural disasters,” or what the insurance companies like to refer to as “acts of God.” A single hurricane can cause billions of dollars of damage, with dozens or hundreds of deaths. But in spite of their seriousness, or partly because of it, scientists, meteorologists, and economists have studied hurricanes in-depth for years in order to better understand where and when hurricanes will strike and how much damage they will do.
In this article, we’ll look at some hurricane basics and the history of hurricane trends. We’ll also consider how those trends seem to be changing, and what hurricanes might do in the future.
Hurricane Basics
At its heart, every hurricane is simply a big storm. It starts over warm water, always in the tropics – the band of earth on either side of the equator. As the storm grows, warm moist air rises, forming dense clouds when it reaches cooler air high above the oceans. Thunderstorms, or whole series of thunderstorms, form when the wind conditions are right, and begin to swirl around a low-pressure system at the center. As the storm moves along the ocean, it gathers energy and strength. Wind speeds increase, and the storm brings torrential rains.
These storms have different names in different places. “Hurricane” refers to a tropical cyclone originating in the Atlantic Ocean or northeastern Pacific Ocean. Elsewhere, these storms are known as typhoons or tropical cyclones.
Tropical cyclones have a distinct lifespan, growing from an ordinary squall to a much larger storm, and then fading back into a rainstorm, often as they pass over landmasses and lose energy. On occasion, this pattern can happen more than once.
Tropical cyclones begin as tropical depressions. At this point, they have sustained gusts of wind less than 38 miles per hour. As a tropical depression begins to build in strength and the wind increases, it becomes a tropical storm. Now, it can have sustained winds up to 73 mph.
Once the storm’s winds exceed 73 mph, a tropical storm becomes a hurricane. That’s not the end of its progression, however. To better help track the severity of a hurricane as it continues to grow, meteorologists classify them into five different categories, known as the Saffir-Simpson scale.
Category 1: Max gusts between 74-95 miles per hour.
Category 2: Max gusts between 96-110 mph.
Category 3: Max gusts between 111-129 mph. A storm that reach category 3 is considered a major hurricane by most warning centers.
Category 4: Max gusts from 130-156 mph.
Category 5: Max gusts greater than 157 mph.
Predictably, Cat 5 hurricanes tend to be the most destructive, although even minor hurricanes can cause widespread flooding and millions of dollars in damage. Notable Category 5 hurricanes include the two most powerful Atlantic hurricanes on record in terms of max wind at landfall: the 1935 Labor Day hurricane, and 2019’s Hurricane Dorian. Both contained sustained gusts up to 185 miles per hour. Hurricane Dorian became the worst natural disaster in the history of the Bahamas, as the storm’s path devastated the country before it moved up the coastline of North America.
One final point to remember about hurricanes. While it’s easy to focus on sustained winds and the immense flooding of a hurricane’s storm surge, those initially powerful gusts aren’t always what brings the most damage. Of the two most costly hurricanes in history, only one was a Category 5 – Hurricane Katrina, in 2005. The other one was Hurricane Harvey in 2017. Both hurricanes caused an estimated $125 billion in damages, and in each case much of the devastation came not from high winds or the initial storm surge, but from secondary flooding as torrential rain overloaded dams and levees.
Hurricanes Historically
Hurricanes are predictable – to an extent. They differ in this respect from tornados, which are notorious for changing paths and behaving apparently erratically. Hurricanes follow general patterns. Some of those we mentioned above – hurricanes begin as areas of low depression, usually off the African coast, and then typically begin to move westward across the Atlantic. By tracking weather conditions, as well as the storms themselves, scientists can determine the likely path of the storm and the likelihood that it will gain strength as it moves.
This is all great in theory, but as hurricanes move westward, those paths can diverge widely. Here’s a good link which allows you to see hurricane paths from previous years. The trick for hurricane trackers is to guess where a hurricane will go, and when. The path a hurricane takes makes all the difference when it comes to the damage it does.
In general, tropical cyclones inflict damage in one of three ways: wind, rain, and storm surge. Storm surge describes the heavy seas and high tides that accompany hurricanes, which are especially devastating to coastal areas. In the words of the USGS, “A storm surge is the increase in sea level, above the natural tides, caused by hurricane winds pushing seawater toward the shore.” The high water resulting from a storm surge can be devastating; Hurricane Katrina, which wreaked havoc along the Gulf Coast, provides a good example in the video below:
Beyond the storm surge, hurricanes inflict tremendous damage through the accompanying rain. All hurricanes can bring torrential downpours, but the amount of rain that falls in any one area along the path of a storm can vary widely. Much hinges on the speed of the hurricane: speed a storm up, or slow one down, and the amount of rainfall in a given area can range from catastrophic to just another day of wind and rain. But for the worst storms, like Katrina, the combination of a high storm surge and heavy rain can lay waste to coastal areas. In the latter case, the rising waters broke through over 50 levees around New Orleans, resulting in flooding to nearly 80% of the city. The hurricane was bad; the rain and the aftermath were even worse.
Perhaps the image most commonly associated with hurricanes is the picture of violent winds whipping at palm trees, overturning cars, and driving water indoors. We define hurricanes by wind speed – not rainfall. While the water often does more damage long-term, hurricane-force winds power the storm surges which can be so powerful that they reshape coastlines. And for some hurricanes, winds wreak most of the devastation. Such was the case with Hurricane Andrew in 1992, which ripped through Florida with winds as high as 177 mph, strong enough to destroy 25,000 homes.
Hurricanes and a Changing Climate
Most scientists agree on two things: (1), the world’s climate is getting warmer, and (2), humans are a large part of the reason why. For hurricane trackers, the big question is how a warmer climate will influence future hurricane activity. What trends are we likely to see?
A recent survey of current studies by the Geophysical Fluid Dynamics Laboratory (part of the NOAA) reached three major conclusions. Regardless of why climate changes are occurring, evidence seems to indicate that in the future, four things will likely come true:
- Sea level rise will make coastal flooding worse during hurricanes.
- Rainfall should increase.
- Tropical cyclone intensities, across the world, should increase.
- The ration of very intense ones to less intense ones, i.e. of Category 4 and 5 tropical cyclones to categories 1-3, should increase.
Sea level rise – Rising sea levels place increasing stress on existing dam and levee systems, such as the ones in Louisiana which were hit by Hurricane Katrina. The impact of higher sea levels partly explains the impact of recent storms – at least some of Hurricane Sandy’s damage on the east coast was likely due to higher sea levels leading to more intense coastal flooding. With sea levels predicted to rise between 1-4 feet in the next century, that impact will only increase.
Rainfall increase – along with higher seas, there’s a good chance that future tropical cyclones will be wetter and slower. The combination of the two will result in heavier rainfall. Combine heavier rains with higher seas, and there’s an increased likelihood of damaging floods in coastal areas.
More intense cyclones/greater proportion of very intense storms – The relationship between the intensity and frequency of storms, and climate change, is a bit more murky. There seems to be some evidence for more intense storms in the future, but possibly a reduction in the overall number of storms.
Out of the top ten most damaging hurricanes in the United States, eight have taken place since 2004. How much of that trend is linked to global warming is difficult to determine exactly, but it seems sure that climate change will impact tropical cyclones going forward.
Hurricanes and the Human Reaction
One of the reasons for the increased hurricane damage since 2004 comes because despite the risks, more people are living and working in coastal areas than ever before. Coastal populations increased by 35 million between 1970 and 2010, and that trend hasn’t slowed in the past decade. This isn’t just a US trend: many of the world’s megacities, like Shanghai, Singapore, Bangkok, Hong Kong, and New York, are built directly on the coast. This means that whether hurricanes become stronger or not, they will probably become more expensive simply because there are more people living in their path.
The battle between hurricanes and people in coastal communities is as old as time, but given the recent chain of hard-hitting storms, people are beginning to respond to the threat of hurricanes in new ways. Here are some of them:
Hurricane-proof building – Any major hurricane has winds in excess of 110 mph; building a home that can completely resist that is virtually impossible. But there are technologies to make homes vastly more hurricane-resistant than ever, and when done correctly, it is possible to build a structure that can resist a hurricane’s pummeling even when everything around it was been wiped out.
Watch the video above for more advice on exact techniques, but it’s worth noting that construction of this sort is expensive, and beyond the reach of most people. Going forward, the big question for developers in coastal areas will be how to balance the cost of repairing devastating damage with the cost of more expensive initial construction.
Hurricane insurance – with ever-increasing numbers of houses being built in hurricane-prone areas, it’s no surprise that hurricane insurance is growing in popularity. Hurricane insurance is actually a combination of policies, usually homeowner’s insurance and then additional flood and wind insurance, which serves to cover most of the damage a hurricane can cause. Since most hurricane damage stems from flooding of one kind or another, there’s even a government program designed to help find adequate coverage: https://www.floodsmart.gov.
Environmental considerations – Even beyond global warming, scientists are increasingly aware that environmental factors influence hurricanes dramatically. Coastal development places growing pressure on natural sand dunes, reefs, and other shoreline features which work as a natural buffer against hurricanes. As populations along the coast increase, so does the need to incorporate natural features as well as man-made levees, dikes, and dams into any plan to mitigate hurricane damage.
Resources:
https://www.gfdl.noaa.gov/global-warming-and-hurricanes/
https://www.nhc.noaa.gov/dcmi.shtml
https://www.cbo.gov/sites/default/files/114th-congress-2015-2016/reports/51518-hurricane-damage-onecol.pdf
https://www.thebalance.com/hurricane-damage-economic-costs-4150369
https://www.theguardian.com/weather/ng-interactive/2018/sep/11/atlantic-hurricanes-are-storms-getting-worse
https://sciencepolicy.colorado.edu/socasp/weather1/pielke.html