North Carolina flooding demonstrates we need a new hurricane rating system
With North Carolina reeling from more than 17 inches of rain from Hurricane Matthew, it’s time to face the fact that the style we measure hurricanes and communicate their likely impacts is seriously flawed.
We need a new hurricane intensity metric that more accurately reflects a storm’s potential to cause death and extermination well inland, rather than the Saffir-Simpson Wind Intensity Scale, which focuses on the potential for coastal injury from high winds and storm upsurge flooding.
So far, Hurricane Matthew has killed 22 people in the U.S ., almost half of which occurred in North Carolina. As of midday Monday, an entire town Lumberton was being evacuated via helicopters and barges, as a river surged through the entire area. A levee infringe may have accelerated the flooding there.
The inland flooding exemplifies the complexity of these storms. In advance of the cyclone attaining landfall, the media spotlight focused on the potential for tremendous gale and storm upsurge damage in Florida. Yet in the end, this event may go down in history as North Carolina’s worst natural disaster on record, due to heavy rainfall.
Saffir-Simpson only measures wind
Right now, the Saffir-Simpson Hurricane Wind Intensity Scale is what we use to communicate how strong a blizzard is. Developed by engineer Herb Saffir and meteorologist Bob Simpson in the early 1970 s, it is based on the maximum sustained gales in a hurricane.
But this ignores the multitude of other threats that hurricanes pose to coastal and inland areas. In the U.S ., Hurricane Matthew, which was the longest-lasting Category 4 and 5 storm on record during the course of its month of October, will be remembered more for its water injury both cyclone surge and inland flooding than its winds, which is what the Saffir Simpson Scale communicates.
With Matthew, the cyclone did some of its worst injury when it was “just” a Category 1 cyclone, slinking along the coast of the Carolinas. The storm’s category may have suggested to people that it was not a huge threat to North and South Carolina, when in fact the opposite was true.
The storm combined with a preexisting frontal system and record high quantities of atmospheric moisture, pumped into the air from unusually warm sea surface temperatures, to crank out torrential, flooding rains.
It’s long been known that water is the biggest killer during hurricanes. So why do we use a scale that only communicates the wind and coastal blizzard surge menace?
The answer is that we just haven’t come up with a better one yet. Or rather, several have been proposed, but none have become a consensus position within the weather community.
For example, a 2006 newspaper proposed a post-landfall hurricane classification system that would incorporate open water storm upsurge, rainfall, duration of hurricane force breezes, maximum sustained breezes, gust rating and minimum central pressure.
Each storm would be assigned numerical values for each variable, and then the storm would be assigned an overall value on a scale of 0 to 100.
Of the Saffir-Simpson scale, the paper, which was published in the Journal of Coastal Research , stated: “Its purpose is invaluable in the pre-landfall window; however, the Saffir-Simpson Scale does not accurately account for the total damage in the post-landfall period.”
The post-landfall intensity scale may have helped communicate the flood threat during North Carolina’s previous record deluge from a tropical storm or hurricane, which occurred in 1999. Hurricane Floyd caused flooding for weeks and killed 36.
In the next week, many rivers in North Carolina could be expected to pinnacle above the Floyd flood records due to Hurricane Matthew.
Jason Senkbeil, a geography professor at the University of Alabama who co-wrote the proposal for a post-landfall hurricane category system, said the Saffir-Simpson scale is useful because of its simplicity.
“The simple 1-5 ordinal Saffir-Simpson Scale get people’s attention and a 3 or higher usually inspire people to take protective action, or motivates those in low lying upsurge or deluge prone areas to evacuate, ” he said in an email.
“In this regard the Saffir-Simpson Scale has been and continues to be useful, ” Senkbeil told Mashable , noting that new storm upsurge products and graphics are helping to communicate other menaces that the scale does not incorporate.
The media, including meteorologists, focused a lot of attention on security threats that a Category 4 blizzard posed to Florida, and much less to the inland flooding prospect. This was similar to past storms, such as Hurricane Irene, which spared New York City much damage but went on to cause record, devastating flooding in New England.
“Every hurricane is different in terms of the types of hazards associated with landfall and we are doing a POOR job of communicating ALL hazards, ” Senkbeil said in an email”My scale was meant to be a post-landfall scale but it could be easily adapted to be pre-landfall.Matthew would have obviously been the water threat type as soon as it left Florida.”
“Although several media outlets were advising for potential flooding from Matthew in the Carolinas, too much attention was devoted to the possibility of landfall on the Florida coast and the health risks wind velocities above 130 mph, ” he said. “Matthew merely had a 25% chance of making actual landfall in Florida.”
Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research( NCAR) in Colorado, said the Saffir-Simpson Scale “has always been seriously flawed.”
However, replacing it, or supplementing it, is not an easy one. “The main headline menace is always the wind velocity and direct damage, which is always local to the coast, ” he said in an email. “The storm surge threat is also local to the coast but depends upon rate of motion of the cyclone and how it syncs with high tide: but it is always growing because sea level continues to rise.”
“The most widespread threat is heavy rains and flooding, ” he told , noting that the size of the rainfall threat is related to the size of the cyclone and the temperature of the ocean where the storm is drawing its energy from.
With Hurricane Matthew, Trenberth said the sea surface temperatures were more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, above average for this time of year, across a broad region that the blizzard drew moisture from.
This added more water vapor to the air, which eventually condensed and fell as torrential rainfall in the Carolinas.
“So it seems to me that three threats need to be assessed but often aren’t, or not adequately, ” Trenberth said.
Another index that has been proposed is the Cyclone Damage Potential, or CDP. This one can be used to estimate the health risks injury a blizzard will cause to offshore facilities. Greg Holland, a researcher at NCAR who helped develop the scale, says work is ongoing to try to extend it to onshore impacts as well.
“The Saffir-Simpson categories are an excellent approach to clear communication on the potential impacts of hurricanes of differing intensity. However, while intensity were critical, focusing on it alone may lead to miscommunication of the actual impact potential, ” he said in an email.
There are still other proposals out there, including a scale that would try to capture the force and region of a storm’s gale field, known as Integrated Kinetic Energy, or IKE.
Each of these has its pros and cons, but no single scale has yet be decided upon and moved forward to an implementation. Hurricane Matthew should be a wakeup call that this needs to happen, soon.
With climate change set to increase rainfall from these massive cyclones, developing a more impacts-focused hurricane scale that includes the inland inundating issue is going to be even more critical.
Such a scale, if it is successful, could save lives, and prevent people from being caught off his guard by torrential, even catastrophic quantities of rain.
Perhaps the people of North Carolina many of whom have told reporters they were caught off his guard by the flooding will have some suggestions, once they get through this ordeal.