Trends: socio-economic, climate change
As mentioned before, New Orleans has a declining population. Even before Katrina the city was facing issues of contraction, under population and decline. However, much of its population still lives in urban areas that are located 1.3 to 3.0 meters below sea level on drained land that consequently keeps on subsiding. Water is efficiently pumped out, but eventually concrete floodwalls were required along the outfall canals to prevent lake surges from flooding the city. The comprehensive levee and pump system now encircling the city provide protection but also seals human development into a slowly subsiding bowl. Still, street flooding commonly occurs during rain storms due in part to the system’s inherent lack of water storage.
The average annual temperature is expected to rise 3.0°C by 2100. The number of named hurricanes passing through the gulf each year (now 11 on average), is projected to increase in frequency and magnitude. At the same time the sea level is expected to rise by 480 mm (18.9 inches). When taking land subsidence into account, New Orleans might be as much as 2.5 to 4.0 meters (8.2-13.1) below sea level in 2100.