Hurricane Katrina - Recipe for Disaster
- Describe the hazards that can cause damage and injuries in a hurricane.
There are three main hazards in a hurricane - wind, storm surges, and inland flooding. Hurricane winds are a minimum of 74 mph and can be more than twice that in more intense storms. They can knock down structures and rip up plants and throw objects into one another with great force. Storm surges are a mound of seawater created under a hurricane by the low air pressure of a storm and pushed onshore by the high winds. A surge essentially turns a coastline into part of the ocean, washing away and drowning everything in its path. Inland flooding is caused by the huge amounts of rain generated by a storm. Heavy and prolonged downpours cause rivers and reservoirs to overflow and fill up low-lying areas.
- What happened to Katrina's winds as it traveled across Florida, the Gulf of Mexico, and into Louisiana and Mississippi? Explain this pattern.
Katrina's wind speed dropped as it moved across Florida, even falling below hurricane strength briefly. Out over the Gulf, the winds sped up very quickly. After landfall, wind speed diminished very rapidly, and Katrina was no longer a hurricane by the time it reached central Mississippi.
A hurricane get its power from the evaporation of seawater - hot moist air rises, and surface winds are pulled in to replace the rising air. When a hurricane is over warm water, this processes happens faster and faster and the storm can intensify. When a hurricane moves over land, it is cut off from its power source and weakens and dies out.
- Why is inland flooding so much deadlier than other hurricane hazards?
Hurricane winds usually diminish rapidly once a storm moves ashore, and until then, people can take shelter from flying debris inside sturdy buildings. Storm surges only affect areas close to the shore. In contrast, heavy rains can occur over a much wider area, even on the outer fringes of a hurricane, and they can continue after a hurricane breaks down into a tropical storm and moves inland.
- Study the animation of the storm surge produced by Hurricane Georges in 1998. Relative to the eye of the storm, where did the highest and lowest storm surges make landfall? Explain the asymmetry.
The storm surge was lowest to the left of the hurricane's eye and highest on the right side of the storm. This is because the winds in a hurricane rotate counterclockwise around the eye. So as the storm moves onshore, the wind on the right side of it is blowing towards the land and pushing the surge ahead of it. On the left side of the storm, the winds are blowing away from the land, and pushing some of the surge back out to sea.
- What is the purpose of levees? How did they make flooding worse in New Orleans when Katrina hit?
Levees are walls made of earth and concrete built along rivers and lakes to keep floodwaters from spilling over the banks. Because of the levee system around New Orleans, large parts of the city were built on land that is actually below the level of the Mississippi River, Lake Ponchartrain, and the Gulf of Mexico. Once the walls gave way, water poured down into these low-lying areas. And then after the rain and storm surge caused by Katrina dissipated, the lake and river dropped, but then the levees kept water left standing in the city from draining away.
- The coastal population of the United States soared during an interval when hurricane activity was relatively low. How might this have contributed to Katrina's death and damage toll?
Some areas are especially vulnerable to hurricane damage - beachfront parcels, low-lying coastal regions, and barrier islands, for example. The danger increases when natural barriers to storm surges, such as deltas, wetlands, and swamps, are filled in or destroyed. But when hurricanes were fairly rare, it was easy to discount the chances of one striking and development occurred in many high-risk areas. And residents who had never experienced a strong hurricane were more likely to ignore warnings to prepare or to evacuate as Katrina approached.
Critical ThinkingHurricanes are disasters that approach in slow motion. Many, like Katrina, begin on the far side of the Atlantic and slowly make their way toward the United States over several days or weeks. They are carefully tracked by satellite and spotter planes, and their likely path is predicted several days in advance. So why are so many people caught in the wrath of these storms? Why don't populations at risk evacuate in time?
Scientists seek to understand and explain how the natural world works. Many of the questions raised in this endeavor have no absolute answers.
Many people choose not to leave. They decide to stay with their homes or businesses for sentimental or economic reasons. Because there are uncertainties in even the best forecast of hurricane strength and direction, many gamble that the storm will miss them or be weaker than expected. Those who have never experienced the ferocity of a hurricane or the speed and devastation of a storm surge often underestimate the risks of remaining in a danger zone.
Other people are unable to leave. Hurricanes affect a very large region, and safety may be many miles away. The poor, the sick, and elderly often lack the means or the ability to make such a journey.
Increasingly, there are logistical barriers to evacuation. Millions of people live in areas of potential hurricane risk. For an increasing number of coastal and island communities, the roads and bridges simply cannot accommodate a full-scale evacuation. Their residents and government officials must choose between the risks of riding out a hurricane near the coast or in a traffic jam with only the flimsy protection of a car.