The effects of changing climate – Hurricanes
Knowing that, if you said “the wind did it,” it’s coming out of the company’s pocketbook, but if you say “it was water,” then it comes out of the taxpayers’ pocketbook, … under this system, we have given the insurance companies the opportunity to stick it to the government every time there was a question, and I think they did.
— Rep. Gene Taylor, D-Miss., speaking post-Katrina
Hurricanes develop from tropical storms when groups of thunderstorms form a vortex. For a tropical storm to develop the energy necessary to become a hurricane it needs warm water like that found in the tropics and the Gulf of Mexico. The minimum water temperature that can support a hurricane is 78°F. According to the first law of thermodynamics, energy can’t be created or destroyed; it can only change form. When liquid water becomes a gas it stores huge amounts of energy. When that water vapor again becomes a liquid, it unleashes that energy, which helps to fuel the hurricane’s destructive winds. Hurricanes are driven by the extra heat energy found in the tropical ocean waters.
Climate Change Effects
According to Tim Flannery in The Weather Makers both “ozone depletion and greenhouse gas accumulation are changing the energetics of the tropopause” (where the troposphere and stratosphere meet) “in ways that can affect hurricane formation” (Flannery). The exact mechanisms aren’t clear, and natural cycles prevent making a clear connection with the increases that are presently being observed, but according to a September 2005 article in Science there is evidence that, in looking at 35 years of data, “a large increase was seen in the number and proportion of hurricanes reaching categories 4 and 5” (Webster).
Tropical storms and hurricanes are named following the letters of the alphabet. In 2005 there were so many of these extreme weather events that meteorologists ran out of pre-assigned names; the remaining storms were named after the Greek alphabet. This is the first time this has happened since hurricanes began being named. Not only are more of these storms forming but their ferocity also appears to be increasing. Some of the recent hurricanes such as Charley (August 2004), Ivan (September 2004) and Francis (September 2004) have overlapped paths damaging some buildings more than once.
On August 29, 2005, about the middle of the hurricane season, which typically runs from June 1st to November 30th, hurricane Katrina hit the Gulf Coast. Within two days 80 percent of New Orleans was flooded, with some homes under fourteen feet of water because the levees were breached. When homes are built on low-lying areas that must rely on aging dikes and levees, they are at a much greater risk than when built in less precarious areas. The magnitude of the disaster resulting from Katrina was so massive that first-aid measures for the hardest hit areas were useless. I visited New Orleans fourteen months after the disaster and in spite of my experience working with damaged buildings I was still amazed at the remaining devastation. The Army Corp of Engineers had temporarily repaired the broken levee I visited. The homes in the area had remained flooded for weeks while the levee was repaired. Entire neighborhoods were decimated and many people have never been able to return to their homes because they no longer exist. The damage from Katrina was extreme and more extreme disasters are likely to occur as the global climate crisis continues.
What You Can Do
Hurricanes present more challenges than high winds and tornados because they are loaded with huge amounts of water. All of the recommendations for protecting your structure from extreme wind should be followed for hurricanes with an even greater attention to detail for preventing water intrusion through windows, doors and other penetrations. Fortunately the hurricane warning system provides a much longer advance alert than is available for wind storms and tornados. Providing you are ready, this will allow you to attend to last-minute details prior to the storm, but don’t wait for the last minute to purchase or install the protection.
Saffir-Simpson Hurricane Scale
WIND ESTIMATE (MPH)
|74-95||Storm surge generally 4-5 ft above normal. No real damage|
|to building structures. Damage primarily to unanchored|
|mobile homes, shrubbery and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage.|
|96-110||Storm surge generally 6-8 ft above normal. Some roofing|
|material, door and window damage of buildings.|
|Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center.|
|Storm surge generally 9-12 ft above normal. Some structural|
|damage to small residences and utility buildings with a|
|minor amount of curtain wall failures. Damage to shrubbery and trees with foliage blown off trees and large tress blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center.|
|Flooding near the coast destroys smaller structures with larger structures damaged by battering of floating debris.|
Category Three Hurricane
WIND ESTIMATE (MPH)
Terrain continuously lower than 5 ft above mean sea level may be flooded inland 8 miles (13 km) or more. Evacuation of low-lying residences within several blocks of the shoreline may be required.
|Storm surge generally 13-18 ft above normal. More|
|extensive curtain wall failures with some complete roof|
|Hurricane||structure failures on small residences. Shrubs, trees and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km).|
|Storm surge generally greater than 18 ft above normal.|
|Complete roof failure on many residences and industrial|
|Hurricane||buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage.|
|Low-lying escape routes are cut by rising water 3-5 hours before arrival of the hurricane center. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required.|
|The Saffir-Simpson Hurricane Scale is a 1-5 rating based on the hurricane’s present intensity. This is used to give an estimate of the poten‑|
|tial property damage and flooding expected along the coast from a hurricane landfall. Wind speed is the determining factor in the scale,|
|as storm surge values are highly dependent on the slope of the continental shelf in the landfall region. Note that all winds are using the US|
|Modified from: National Hurricane Center, NOAA: www.nhc.noaa.gov/aboutsshs.html Downloaded 9/16/06|
It is not possible to completely protect an above-ground home from a direct hit by a hurricane, but there are many steps that can be taken to help reduce and limit the damage. Windows should not be left open since this will permit entry of massive amounts of water.
All the recommendations for wind and tornados apply to hurricanes plus the following.
- Pay special attention to sealing all roof underlayment seams. A peel and stick membrane covering the entire roof underlayment may make sense for warm humid climates, but should be used with caution in mixed-climates and may be a big problem in cold climates with unvented attics.
- If you can safely take the time before evacuating, seal attic gable vents, and use duct tape to seal eave vents and other penetrations like those for clothes dryers or exhaust vents. Don’t forget to remove the tape after the storm has passed.
- Because of the longer warning time for hurricanes, temporary storm shutters can be installed. These can be made of plywood, but are even better if constructed from polycarbonate material which will protect the window while admitting light. The Engineered Wood Association offers a free design guide for window shutters at apawood.org. You will need to sign up with a login password, and then search the publications section for “shutters.”
- Seal all cracks and penetrations with a high quality caulk material to keep out water, but always leave a drainage path for water that gets behind materials.
- Below-ground shelters are not an option since they could become flooded with water. The best plan is to prepare the building as best you can to weather the storm and follow the recommendations for a safe and orderly evacuation if instructed.
“Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low.”
(IPCC 2007 page 11
Summary for Policymakers)