GEOG 2152F: Geography of Hazards
Video: Hurricane Katrina (The Storm that Drowned a City)
1. What is a tropical depression? Describe the origins of Hurricane Katrina.
- starts off as a small storm called a tropical depression
- Tropical depression: a center of low atmospheric pressure
- In the warm waters of the eastern Atlantic, water vapor rises from the ocean then cools,
forming clouds and releasing heat energy which fuels the storm
- This sucks in more warm air, generating strong winds, which shoot upwards
- When this rush of air hits the stratosphere, it flattens out, and, influenced by the Earth's
rotation, the storm starts turning counterclockwise.
- As soon as the winds reach 39 miles per hour, the depression is considered a tropical
storm (a day later after Katrina starts off as a tropical depression, the Hurricane Center
upgraded it to a tropical storm)
- Roughly half of all tropical storms become hurricanes
2. How have we been improving the forecasting of hurricanes?
- Hurricane forecasts are improving due to a greater understanding of atmospheric
dynamics and more extensive satellite coverage.
- Relying very heavily on remote sensing via satellites
- But if more data needed, sent out the Air Force hurricane hunters fly right into the
approaching storm, so external sensors record wind speed, pressure and temperature to
build up a more detailed picture of Katrina
o new piece of technology has been added: dropsonde
o released through a chut in the floor, as it floasts down to the surface it radios back
o acts like a weather balloon: collecting temperature, relative humidity, and
pressure; also a GPS module that will be affected as it shifts from one point to the
next (giving wind direction and wind speed at different points in the storm)
- also have faster supercomputers at Hurricane Center, also using improved computer
modeling so longer-day forecasts are getting more accurate
- however, intensity is still difficult to predict because the inner storm can change minute
3. What was the engineering approach to protect the city? What were its limitations?
- To protect the growing population, the state built earthen levees back in 1900s
- But these banks can burst
- The Army Corps of Engineers and the federal government build and repair levees
(especially the Mississippi River levees in the city of New Orleans and southern
- New Orleans has two types of levee: the original earthen levees and more recently built
concrete and steel floodwalls
- However, these levees can only withstand up to Category 3 hurricanes. 4. What role do wetlands play? How have they been altered and what has been the impact?
- The wetlands used to provide defense against Hurricanes
- The Mississippi River conveyed tons of silt and soil to the coast each year. Every spring,
when the river flooded, the wetlands were stre