By Jonny Lupsha, Wondrium Staff Writer
Hurricane Ida continued its deadly path into New York City. Louisiana has already suffered problems from storm surge caused by Ida, while flood damage ravages New York. Inland flooding is a fatal consequence of hurricanes.
Hurricane Ida has killed more than two dozen in the tri-state area of Pennsylvania, New Jersey, and New York. In addition to deaths, Ida’s heavy rains caused historic flooding—more than six inches of rain fell in a few hours Wednesday. Ida’s rains also led to major disruptions in New York City’s transit system, with hundreds being evacuated from subways and train cars.
While the single deadliest factor of a hurricane is storm surge, which Louisiana has seen recently, inland flooding is the second. In his video series The Science of Extreme Weather, Professor Eric R. Snodgrass, Director of Undergraduate Studies for the Department of Atmospheric Sciences at the University of Illinois at Urbana-Champaign, explained the perils of hurricane-based flooding.
Rain, Rain Go Away
Inland flooding related to hurricanes is caused by massive amounts of rainfall.
“In fact, even though the wind-blown waves of storm surge cause more fatalities, the true power of a hurricane lies in its clouds,” Professor Snodgrass said. “Hurricanes efficiently draw evaporated water into the lower atmosphere. As this air rises, it cools to the point in the atmosphere where it’s saturated. Condensation begins and clouds form.”
According to Professor Snodgrass, it takes 2,500 joules of energy to vaporize a single gram of water, while typical hurricanes hold two quadrillion grams of vaporized water. This means the energy content in the cloud field of a hurricane is equivalent to 1,000 megaton nuclear bombs.
“A typical raindrop is about one millimeter in diameter; big raindrops can grow to be four or five millimeters in diameter,” he said. “Large raindrops have a difficult time surviving as they fall, because they deform and shear apart into smaller drops. Sometimes large drops collide and shatter into dozens of small drops.”
Despite the size of the raindrops, hurricanes make a lot of rain.
A Tale of Two Hispaniolas
Drowning isn’t the only hazard associated with hurricane rainfall.
Haiti and the Dominican Republic share the island of Hispaniola. Much of Haiti has been deforested over the centuries, while the Dominican Republic has not. The stark difference between the tree coverage in the two countries made a world of difference in 2004 with Hurricane Jeanne.
“When the rains from Jeanne hit the island, mudslides and landslides and flooding killed over 3,000 Haitians; only two dozen Dominicans lost their lives from the same storm,” Professor Snodgrass said. “Without trees to hold the soil, gravity can easily cause saturated ground to move and flow down the slopes into the villages and towns in the valleys.
“Poor land management multiplies the effect of heavy rainfall to make the greatest disaster here even worse.”
According to Professor Snodgrass, the worst combination of events to happen to any landfalling hurricane is for the hurricane to slow down and stall over a mountainous region that has poor land management. Unfortunately, Haiti’s natural geography and the centuries of deforestation make that nightmare a reality.
“That is why Haitians suffer so much every time a tropical storm passes over the Western part of this island,” he said.