Hurricanes and the U.S. Gulf Coast: Science and Sustainable Rebuilding

Summary of Report

The knowledge available among AGU members provides scientific expertise on nearly all of the physical environment of the dynamic Gulf Coast ecosystem complex. Intelligently rebuilding features such as fisheries, oil fields, seaports, farms, and wetlands after hurricanes Katrina and Rita will require “a well-constructed collaborative effort to maximize the role of science in decisions made about the rebuilding,” wrote Charles Groat, former director of the U.S. Geological Survey, in a news article published in Eos that stimulated an AGU meeting of experts.

As a step toward developing a scientific basis for safer communities along the Florida-Alabama-Mississippi-Louisiana-Texas coastline, AGU convened an interdisciplinary 'Conference of Experts' on 11-12 January 2006 to discuss what we, as Earth and space scientists, know about the present and projected environment in New Orleans and the Gulf Coast areas affected by the hurricanes of 2005. Twenty scientists, all experts in the fields of science relevant to the Gulf Coast, met to consider ideas for a coordinated effort to integrate science into the decision-making processes necessary for the area's sustainable rebirth. Political, economic, and social issues were intentionally not discussed. Nevertheless, it was recognized that these issues are intertwined with science and are of paramount importance. This report contains a summary of the discussion and is intended to be helpful in providing scientific understanding useful in redevelopment of the affected area.

The objectives of the meeting were to review and assess the scientific knowledge in the areas most relevant in hurricane protection, to identify gaps in knowledge that could be filled by focused research, and to propose mechanisms to link science to the most effective reconstruction of New Orleans and other coastal areas affected by the recent hurricanes. The meeting attendees considered seven topics addressing the current understanding, near- term needs, and longer-term directions for: hurricanes, storm surge and flooding, subsidence, climate change, hydrology, infrastructure, and disaster preparedness and response. The messages from the conference are as follows.

Hurricanes

While all hurricanes are detected before landfall and their trajectories known to some degree, predictions of cyclone intensity and structure still contain great uncertainty. Although there have been substantial increases in the accuracy of hurricane track prediction over the past decade, seasonal predictions have shown little skill, for example, predicting an increasing number of hurricanes when fewer actually occur. European ocean-atmosphere models, however, have demonstrated improved capability and may provide more reasonable approximations in the future. Rising sea surface temperatures, routinely observed through infrared and microwave emission satellite sensors, increase the tropical cyclone heat potential and contribute to tropical cyclone formation and their intensification. The conference participants proposed the use of improved seasonal forecasts such as those being applied in Europe.

Storm Surge and Flooding

The basic physics of storm surge is well understood. Remarkably accurate numerical models have existed for approximately 25 years in the United States and abroad for geometrically simple coastal areas. Recent developments have allowed modeling of complex regions such as the Louisiana shoreline that include channels, levees, and buildings.

Nevertheless, better wind data, enhanced shoreline topography, and improved techniques to assess the location and range of flooding are necessary in storm surge models for simulating the range of flooding probabilities. Such modeling scenarios can be used to predict the extent of damage such as levee overtopping, were such an extreme event to take place. In the longer term, advanced high- resolution data could provide even better approximations of inundation and expected damage from flooding, thus allowing cities and regional disaster mitigation agencies to prepare an appropriate response to an impending disaster.

Subsidence

Natural processes as well as human impacts have contributed to subsidence, the sinking of land over time, along the Gulf Coast. Presently, there is considerable discussion and debate among the scientific community regarding mechanisms and rates of subsidence in the Mississippi delta area. Regional faulting, forced drainage, oil and gas extraction, and groundwater withdrawal all have led to lowering of the elevation of highways and levees below their originally designed levels.

As a result of subsidence, new U.S. Federal Emergency Management Agency Base Flood Elevations maps that will be available for the area in 2007 may not be accurate; yet those maps will form the basis for flood control and establish levels for rebuilding. In the future, levees and other flood control systems should be designed and built to account for the amount of sea level rise and predicted subsidence expected over the design life of the structure. In designing new structures, consideration should be given to likely changes over time in storm surge, subsidence, and sea level. New and improved instrumentation would allow researchers to make better predictions of geological and subsidence processes.

Climate Change

There are strong theoretical reasons to expect that warming of the oceans already has led to more intense hurricanes and will continue to affect tropical storm characteristics. Increasing ocean temperatures also cause sea level to rise due to thermal expansion and thus enhance storm surge. It is well established that a sea surface temperature of at least 26°C (79°F) is required for hurricane formation.

Recent analyses have found that the frequency of intense hurricanes and severe rainfall has increased in recent decades. Hurricane strength and numbers are projected to increase further with rising ocean temperatures. The hurricane climatology of the twenty- first century will be quite different from that of the twentieth century. Planning should take into account the strong probability of more frequent and more intense hurricanes. In the near future, prediction models will be able to provide notice of exceptionally strong hurricane seasons more in advance than is presently possible. As these advances continue, and as more is known about the fundamental physical basis of climate change, hurricane response plans can be continually improved.

Hydrology

Human settlement in New Orleans and throughout the Gulf Coast has greatly modified the natural conditions of the Mississippi River system. In New Orleans, for example, canals have been dredged for navigation and drainage, levees that limit flooding have been raised, tidal wetlands have been eliminated, and dams and locks have been constructed. As development projects have continued and expanded, the mechanisms that had preserved the Mississippi delta in the face of subsidence and erosion have been largely stifled. While the rebuilding of coastal communities has to account for such conditions, long-term flood protection will likely require reestablishing some natural systems such as wetlands that serve as a natural barrier adding some protection from storm surge and flooding.

Infrastructure

When floodwaters from hurricanes Katrina and Rita spilled through the Gulf Coast and breached the levee system in New Orleans, infrastructure damage ranged from unusable roads and bridges to inoperable telecommunications, electrical, and satellite observation systems. The breakdown of communications, both physical and organizational, will require extensive attention and modification. Additionally, ravaged systems such as navigation channels and coastal ports will require renovation and better protection against future damage. Improved models supported by a better understanding of the region's natural systems are needed to plan a unified system of storm protection.

Disaster Preparedness and Response

No matter how resilient the new Gulf Coast may be, preparation for future hurricanes will require development of the capability for massive and timely responses to protect resources and lives. Key to an effective response are detailed scenarios, maps, and visualizations of the affected areas. In addition, training of first responders is necessary so they can react to ever changing scientific data. Most critical is accurate information with three to four days notice that would provide time for evacuations, if necessary. Improved forecasts of hurricane trajectory, intensity, and structure are most vital to completing these tasks.

Future Considerations

The key objective of the conference of experts was to ensure the integration of science into the overall reconstruction efforts after the recent hurricane disasters along the Gulf Coast. Given the breadth of the Earth and space science topics within AGU's purview, the organization and member scientists are well prepared to discuss and demonstrate the relevance of sound science to decision-makers charged with rebuilding when future catastrophes strike.

Several recommendations emerged from the conference that would continue the dialogue between scientists and planners at all levels. The suggestions are as follows:

(1) Establish a multidisciplinary steering committee to maintain an overview on reconstruction and new threats to the region from natural disasters, and charge that committee with monitoring the rebuilding and identifying key scientific issues and assets to address these issues;

(2) assemble a database of experts who would be available to provide scientific guidance as needed; and

(3) provide periodic assessments of reconstruction and planning efforts.

Successful and sustainable reconstruction of New Orleans and the Gulf Coast and the effective planning for future hurricane events must incorporate the best available science. This can only be ensured by strong continuing interaction among scientists, planners, and decision-makers at all levels.