Natural Hazards Observer, May 2009

“Exploring links between natural hazards and global warming” by William Travis (Natural Hazards Observer, March 2009) answers some questions and raises many more while advocating for further cross-fertilization between the hazard field and the climate research community.

Cross-fertilization should not stop with the hazards and the climate research communities, but must engage several sectors – the emergency management community, the building design and construction professions, professional licensing sectors, and higher education.

This process must go beyond exchanging of knowledge across fields and disciplines. It must aggressively foster contributions, participation, collaboration, and action by practitioners in fields that up to now may have barely acknowledged one another.

One clear example is the current scientific debate on whether climate change has caused an increase in tropical cyclogenesis and/or the incidence of major hurricanes. Respected scientists argue that with increased global warming, we have seen a direct increase in the annual number of major hurricanes across several oceanic basins worldwide pointing to a link between global warming and tropical cyclones.

Other equally respected scientists argue increases in the number and intensity of tropical cyclones are just the result of multidecadal cycles of variability, independent of global warming.

To set the context for my argument, the following must be considered:

  • On the issue of climate change, research and public discourse in the United States has taken place against a background of noise created by political interference with scientific work and campaigns of disinformation fueled by special interests over the past several years.
  • Over the past decade or so in the United States and globally, the emphasis of climate change work has been on greenhouse gas emissions, the use of non-renewable energy sources, and on what to do to mitigate the impact of human activity on the global climate, with much less attention paid to adaptation to reduce the potential for damage to humans and the built environment from climate change
  • The national emergency management community has by and large paid little attention to the links between climate change and natural hazards. As a result, state and local mitigation plans, which have been required by law since 2000, usually fail to include climate change, sea level rise, or extreme precipitation in hazard assessments.
  • The building design and construction professions – the engineering sector in particular – have been mostly absent from the climate change arena, especially with regard to adapting the built environment to potential impacts from climate change.

A commonly held view among architects and engineers is that, with regard to potential damage from hazards exacerbated by climate change, all you are required to do is meet the pertinent building code.

Against this background emerges a position that can be simply stated as follows:

  • Hazards, whether natural or anthropogenic, must be viewed as sources of potential damage.
  • Vulnerability results from the interaction of human activity with hazards.
  • All hazards incorporate damage components, which have the capability of causing direct damage to the built environment or to human activity. Wind-velocity pressure applied to buildings by hurricane winds, and hydrodynamic pressure applied to buildings and infrastructure by storm surge are examples of damage components.
  • Climate change must be viewed as a slow-acting hazard.
  • Sea level rise is already exacerbating storm surge during hurricanes. It will continue to do so into the foreseeable future. Sea level rise results in deeper coastal waters, which in turn lead to higher, faster flowing storm surge, which in turn produce higher waves. The net results are much stronger hydrodynamic pressure and wave impact on buildings affected by storm surge generated by hurricanes.
  • Global warming has increased the capability of the atmosphere for holding moisture and may be elevating the threshold for precipitation to occur. Empirical data shows an increase in the incidence of extreme rain events in certain locations. These conditions will exacerbate the potential for damage during “wet” hurricanes.
  • The connection between sea level rise and the exacerbation of storm surge, and between global warming and extreme precipitation events, is clear. Based on this, the link between climate change and hurricanes is undeniable.

It is imperative that we take a careful look at the method currently used for establishing building design criteria in regions vulnerable to hurricanes, specifically regarding external loads acting on buildings as a result of storm surge impact.

At present, a structural design team uses the American Society of Civil Engineers-7 standard to establish minimum design loads for buildings and other structures, including those exerted by wind, flood, storm surge and wave impact. Applicable parameters for calculating such minimum design loads on a local or site-specific basis come from a range of sources such as Basic Wind Speed map, pertinent FEMA Flood Insurance Rate Maps (FIRM), or the appropriate Surge Atlas based on the NOAA Sea, Lake and Overland Surge from Hurricanes (SLOSH) model.

In the case of storm surge, the sources of information used to determine surge depth and wave height at a given location, such as the FIRM, SLOSH runs, and Surge Atlases, estimate these parameters with respect to a reference point such as National Geodetic Vertical Datum of 1929 or North American Vertical Datum of 1988, which are measurements of mean sea level as of 1929 and 1988, respectively, and are largely based on historical events.

A critical problem with this approach is that the ffect of continuous sea level rise is not taken into account requiring corrections to establish accurate parameters for storm surge depth and wave height at the specific project location. The main consequences of this are:

  • Buildings are being built today using minimum design criteria based on historical data and outdated points of reference that, in the specific case of storm surge, do not include the current and future effects of sea level rise.
  • Because of this, new buildings in coastal locations may suffer external loads from storm surge and wave impact in the future, which exceed their original design criteria by a factor of 150 to 200 percent, creating the potential for catastrophic damage.
  • New buildings on sites that, on the basis of current storm atlases, are outside the influence of storm surge impact or subject to minimal levels of storm surge may find themselves in more hazardous storm surge zones in the future as a result of sea level rise, potentially subject to loads from hydrodynamic pressure and from wave impact that will exceed their minimum design loads.
  • A large portion of the existing stock of buildings and structures in the hurricane-vulnerable states is at risk of future catastrophic damage from storm surge and wave impact, depending on when they were built.

This dire scenario requires a critical paradigm shift that must at a minimum include the following elements:

  • The scientific community needs to acknowledge the influence of climate change in the exacerbation of specific damage components of hurricanes.
  • The emergency management community needs to start viewing specific components of climate change as hazards, hence as sources of potential damage to the built environment, to human activity and to the environment.
  • The emergency management community needs to include such climate changedriven hazards in risk assessments that support the federally required mitigation planning.
  • The scientific community – in collaboration with the engineering sector and the emergency management community – must pursue research with the objective of enhancing capabilities for establishing realistic parameters for future storm surge depth, rate of flow, and wave heights, which can be used in defining design criteria for building construction.
  • Building design professionals, architects, and engineers must radically change the current approach to building design. A method that is based on future potential loads, especially in the case of storm surge and wave impact, that may occur during the expected service life of a new building needs to replace the existing approach.
  • The higher education community must upgrade its curricula to reflect these critically needed changes, and to equip future building design professionals, emergency managers, and scientists with practical tools to reduce the potential for damage from the impacts of climate change through the adaptation of buildings, structures, and infrastructure using forward-looking design criteria.
  • The regulatory community must incorporate pertinent requirements in the professional licensing process, to ensure that professionals in many fields are equipped with the knowledge to confront current and future impacts of climate change.

The time to bring these changes about is now.

You can read Ricardo’s original submission here.