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Volume 8 Issue 1
July 2013

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Climate Change Preparedness

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climate change

 

"Community Vulnerability Assessments Start with Sound Science to Understand Present and Future Risk."

Many communities are starting to plan for climate change, and specifically sea level rise and storm surge risk. A critical step in the process is a vulnerability assessment, which addresses a vast range of factors related to critical infrastructure, electrical systems, water supply, evacuation planning, and other public functions. A vulnerability assessment typically includes:

  1. Assessment of current vulnerabilities;
  2. Projection of future conditions;
  3. Evaluation of processes and flooding pathways; and
  4. Analysis of system sensitivity (e.g., where might a small change force a large system response) and resiliency (e.g., is the system prepared to accommodate changes).

Specific actions that communities can take now include:

  • Determine regional and site-specific flooding risk through assessment of physical processes
  • Identify elevations of flood-prone buildings and infrastructure
  • Identify property-specific pathways and vulnerabilities to flooding
  • Develop cost-effective measures to increase resilience
  • Pursue integrated strategies to maximize adaptations
  • Identify uncertainties, and make a recommendations for monitoring data to guide future planning and investment decisions

One key element of the vulnerability assessment process is understanding the current and future risks of flooding. Woods Hole Group has supported vulnerability assessments by measuring, modeling, and forecasting flooding due to storms, sea level rise, climate change influences, and combined effects. Examining community vulnerability cannot be limited to projecting estimated average sea level rise over a period of time. A complete vulnerability assessment also recognizes the dynamic physical processes and timing associated with storms, along with increasing risks of sea level rise and climate change. Figure 1 illustrates the flood elevation forecast for East Boston in 2010, 2050, and 2100 for mean high water (daily risk), a 1-year storm, and a 100-year storm. For example, a 1-year storm in 2010 was expected to produce a flood elevation of 7 ft, exceeding the elevation of mean high water in 2050 even including a high rate of sea level rise. Therefore, a typical annual storm in Boston today may cause more flooding than sea level rise over the next 40 years. For a community embarking upon a vulnerability assessment, it is important first to understand the tremendous risk many communities face already today. Furthermore, a 100-year storm in 2010 is expected to produce a flood elevation of 10 ft, actually lower than flooding projected at mean high water due to a moderate level of sea level rise by 2100. Thus, the potential daily influence of sea level rise 100 years from now is expected to be comparable to a severe storm today. It is imperative, then, for communities to plan now for today’s risks, but also for future impacts less than 100-years; a time scale affected by building and zoning decisions today.

Figure 1.  Flood risk in East Boston between 2010 and 2100 for mean high water, 1- and 100-year storms.
Figure 1. Flood risk in East
Boston between 2010 and 2100
for mean high water,
1- and 100-year storms.

 

Another meaningful comparison for a community vulnerability assessment is the timing of storm surge compared to normal tidal fluctuations. Figure 2 illustrates the normal predicted water level (blue line), the observed water level (red line), and the surge (green line) during Hurricane Sandy in Boston. The highest surge levels of 4+ ft, while not nearly as severe as those observed in New York, New Jersey and surrounding areas, actually occurred near low tide in Boston thereby limiting flooding to roughly a modest ~3-year event. Had the highest surge occurred in Boston at high tide, the combined water level would have approached 100-year levels; this for a storm that did not directly impact the Boston area. While nothing can compare to the devastating impacts caused by Sandy’s direct impact in the mid-Atlantic, with its high tide range Boston may have been spared by the coincidental timing of low tide.

Figure 2.  Predicted and actual water levels in Boston during Hurricane Sandy.
Figure 2. Predicted and actual water levels in
Boston during Hurricane Sandy.

 


Incorporating the dynamic influence of combined storm surge, waves, winds, and tides into community vulnerability assessments can benefit from application of numerical models. Typical flooding studies sometimes focus on the “bathtub” approach, which essentially forecasts future sea level rise and then compares the forecast elevation to the surrounding land elevations and assumes every property lower than the forecast sea level will be flooded. This type of analysis, while useful at cursory planning levels, is not adequate for a vulnerability assessment. Storms do not produce uniform water levels, and are not the same everywhere due to the dynamic nature of storm events (e.g. winds, waves, etc.). There also are not necessarily flooding pathways to every low-lying property – a low-lying property may be disconnected from the water source. Application of physics-based numerical models offers the capability to simulate more realistic flooding potential in detail (Figure 3). Properly applied models also offer the opportunity to simulate future water level and intensified storm conditions, both of which are not included in traditional flood studies (e.g., many FEMA studies only project flood zones based upon storms that occurred in the past). These models can then also be used to potential benefit of engineering adaptions. For example, integration of an engineering adaption (e.g., seawall, beach nourishment, etc.) can be added to the model. The combined storms and sea level rise modeling can be re-simulated, and the change in flooding levels, locations, and patterns can be assessed. Model results can then be tied to an economic model to determine potential cost benefits of a specific engineering adaptation. Simulations of a large number of storms along the Gulf Coast for the 20th and 21st century climate showed future storms are anticipated to produce surge elevations several feet higher (e.g., 100-year storm level more than 3 ft higher 100 years in the future).

High resolution storm surge model grid in Gulf of Mexico.
Figure 3. High resolution storm surge
model grid in Gulf of Mexico.

 

Once communities understand the current and future risk, an informed planning process can proceed. In Woods Hole Group’s experience, it is important for communities to develop a preparedness plan with consideration of various time and spatial scales. Certain decisions can be made community-wide, whereas other strategies are required for individual properties or buildings. Likewise, certain decisions can be made in the short-term, while other decisions can be phased over time as more data become available. Although it is not feasible or affordable for a community to modify its infrastructure today for an uncertain flood scenario 50 years in the future, defining the risks today, in the face of uncertainty, is essential. Certain critical infrastructure may be at risk now, requiring immediate attention, whereas other affordable plans can be made when continuing monitoring data warrants action. Appropriate engineering adaptations are site-specific, but may include:

  • Modular or phased approaches (e.g., strategically located modular seawalls at critical flood pathway locations that can be increased over time)
  • Facility improvements/upgrades (e.g., elevated, floating, or even “floodable” developments)
  • Soft engineering solutions (e.g., wetland restoration, living shorelines, beach nourishment and dunes)
  • Hard engineering solutions (e.g., seawalls, dikes, storm barriers)
  • Managed retreat (e.g., where financially feasible or not already developed)
  • Improved evacuation planning

Climate change related flooding is a reality and predicted to increase. Many communities also face flooding risks today that are not well understood. Proper climate change planning requires sound science, and will involve multiple activities on different spatial and temporal scales. Preparing for increased coastal flooding involves implementing phased plans, including integrated improvement and maintenance plans to reduce life cycle costs. Most importantly, future planning will require dedicated efforts of diverse stakeholders, and coordinated efforts across all sectors of communities.


Submitted By:
Bob Hamilton, V.P. and Coastal Engineer
Kirk Bosma, P.E., Team Leader and Coastal Engineer

Contact Information:
Woods Hole Group – Falmouth
81 Technology Park Drive
East falmouth, MA 02536
P: 508-540-8080

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