Texans commonly proclaim that everything is bigger in their home state. A stalled hurricane/tropical storm known as Harvey has dumped over 50 inches of rain at one gauge and more than 20 inches across much of the Houston region. This has set a record for the largest multi-day precipitation event in the continental U.S. The consequences of this excessive rainfall have been flooded homes and streets and massive disruption to this huge urban territory. The tragedy dramatically points out that large Gulf Coast cities are susceptible to massive downpours and are not well suited topographically to cope with the ensuing runoff.
Twelve years ago, almost to the day, New Orleans suffered a major flood that a very different hurricane unleashed—Hurricane Katrina. Levee failures and storm surge, not relentless rain, inundated some 80 percent of the city. Despite quite different circumstances, these two events showcase important aspects of historical urban development and hazard management in the Gulf Coast.
Both cities have sprawled beyond the safe habitable areas of their territories. New Orleans built, expanded, or improved its hurricane protection levee system after the four major storms of the last century—1915, 1947, 1965, and 2005. Protective barriers enabled the city to drain wetlands and expand off the narrow swath of high ground along the river. Within the city and adjacent Jefferson Parish, some of the newly protected land subsided to depths 10 feet or more below sea level. This situation amplified the impacts of floods when the levees failed in 2005. Additionally, simple heavy summer downpours can flood the city which is encircled by levees and relies on pumps to lift the water out. The city has a long history of coping with floods.
Houston is much larger than New Orleans and has pushed residential neighborhoods to low lying areas near the industrial axis along Buffalo Bayou and westward across the Katy Plain. There is little topographic relief in this city. The surrounding environs and the numerous slow-moving waterways that pass through the city are unable to move massive amounts of water to the nearby gulf with any efficiency. Pumping of groundwater and oil from beneath the city has caused fairly widespread subsidence (the causes are different in Houston, but the consequences are similar)—diminishing the fall between developed areas and the Gulf of Mexico and thereby reducing the potential speed of urban runoff. It also enlarges the territory susceptible to inundation. The countless acres of road surface, parking lots, shopping centers, public buildings, and other impermeable surfaces increase the volume of water that moves to the inefficient bayous. Consequently, the city has long suffered from and tried to overcome its frequent floods. At least it can rely on gravity to move runoff to the Gulf. Development, more than rainfall, in both cities has enlarged the flood risk.
Growth has also catapulted both cities to the size where they are unable to swiftly respond to extreme events. When the levees failed in New Orleans, all response plans were upended. The deployment of government resources was delayed for a variety of reasons but most importantly because of the flood waters within the city prevented vehicular rescues and forced the use of less efficient helicopters and boats. In the immediate absence of formal relief organizations, volunteers set up food and medical dispensaries. Neighbors assisted neighbors and local boat owners set to work rescuing those in need. Even after the majority of its citizens had evacuated, the one shelter-of-last-resort, the Superdome, was unable to house the thousands displaced by high water. People broke into schools which had served as neighborhood shelters in the past. Food and water ran out and formal relief was slow to arrive. Eventually it did, but tragically too late for some who perished in the sweltering heat and humidity.
In recent days, Houston with more than 4 million residents experienced flooding over about 30 percent of the city. There was no evacuation order and most residents, not expecting water to invade their homes, sheltered in place. As the bayous rose, low roads were covered. Cars stalled as families tried to escape. Routes to high ground became impassable. There were insufficient resources on hand to rescue the thousands that were stranded in flooded homes. A so-called Cajun Navy mobilized from Louisiana and were joined by Texan sportsmen and professionals. The volunteers launched their crafts into the water-filled streets and ferried the stranded to safety. In the first few days, evacuees quickly overwhelmed shelters, which ran short of food and were unable to maintain the restrooms. Stores and restaurants, severed from their suppliers, quickly ran out of basic supplies. Emergency resources are arriving now that the rains have stopped. From afar it appears that the response has been orderly, but on the ground the response lagged behind demand. FEMA anticipates some 500,000 inhabitants will apply for assistance and that number may grow. In both Houston and New Orleans, the immensity of the event and the sheer number of people involved overwhelmed the short-term emergency resources. Social systems were not able to scale up at the pace demanded by impacted citizens.
Minorities, the aged and infirm, and the poor were disproportionately affected by Hurricane Katrina, mainly due to their inability to evacuate. Early reports and the pre-storm geography of race, ethnicity, and poverty suggest similar hardships have been imposed on disadvantaged communities in Houston. In the absence of an evacuation order the impacts were less concentrated among the disadvantaged. Nonetheless, minority and low-income housing in Houston is largely situated in the eastern, lower lying areas toward the outlets for the creeks and bayous. Flooding has been pronounced in these areas and likely the greatest demands will come from these areas.
Both cities rely heavily on petrochemical industries which have been contributors to the release of greenhouse gases and global warming. Firm dedication to this economic mainstay has fostered local political cultures that dismiss climate science. By discounting the role of the region’s main economic engine in contributing to conditions that make extreme rainfalls more likely, elected officials place their constituents at greater risk. Release of dangerous chemicals from industrial sites adds to the complications of the flooding. In addition to Katrina and Harvey, floods have all too often affected the axis between Houston and New Orleans since Tropical Storm Allison in 2001. Despite the frequent warnings these storms provide, there is a tendency to label them as rare and beyond the normal range of precipitation. This denies both the past and a potentially more extreme rainfall future.
The most arduous aspect of this event lies ahead. Recovery is the long slow phase of disaster. New Orleans is still in its recovery twelve years after Katrina. One of the troubling aspects of the rebuilding phase is that homeowners with insurance and those who receive other forms of assistance tend to rebuild in place. Indeed, the flood insurance program is structurally oriented to do just this, and some 90 percent of Louisiana residents who received funding through the Road Home program remained on their property. Insurance may pay for repairs, but it does not offer compensation for the trauma and anxiety associated with the long recovery process. By paying home owners to rebuild in place, this economic tool exposes them to the same risk in the future. Repeat flooding is common in New Orleans and Houston, and the warming climate increases the risk of extreme rainfall and exposure to inundation.
Craig E. Colten is the Carl O. Sauer Professor of Geography at Louisiana State University. He is the author of An Unnatural Metropolis: Wresting New Orleans from Nature (2005); Perilous Place, Powerful Storms: Hurricane Protection in Coastal Louisiana (2009); and Southern Waters: The Limits to Abundance (2014).