Comparing Sea Level Rise Adaptation Strategies in San Diego: An Application of the NOAA Economic Framework
The San Diego Regional Climate Collaborative worked with local jurisdictions to analyze the costs and benefits of different coastal resilience strategies in two San Diego, California jurisdictions (the cities of Del Mar and Carlsbad). This report presents the quantified economic value of properties at risk from sea-level rise impacts, and the evaluation of the costs and benefits of a range of adaptation strategies, including protection, accommodation and retreat. The study found that all of the adaptation strategies evaluated had a positive return on investment given sea-level rise projections, some delivering over $70 of benefits for a $1 investment.
In terms of risks, the study quantified the economic value of properties at risk of damage or loss under different sea-level rise scenarios (including risks from both chronic inundation flooding as well as coastal flooding caused by the combination of increased sea-levels and coastal storm events). Impacts from bluff erosion were evaluated, and the Del Mar assessment also looked at contributions from river flooding. The costs of both primary impacts (damage or loss of property and infrastructure) and secondary impacts (e.g., business interruption, lost tourism, and clean-up costs) were considered. The City of Carlsbad evaluated planning scenarios from 2050 to 2100, whereas Del Mar evaluated planning scenarios beginning in 2030 out to 2100.
Different adaptation strategies (called “action scenarios”) were evaluated, including:
- Natural or engineered protection, including beach nourishment and hard armoring;
- Accommodation, such as elevating structures; and
- Managed retreat, such as acquisition and demolition of structures.
The study authors applied the National Oceanic and Atmospheric Administration (NOAA) framework, What Will Adaptation Cost? An Economic Framework for Coastal Community Infrastructure. To comparatively assess the costs and benefits of different adaptation strategies in San Diego jurisdictions, the authors took the following steps :
- Establish Baseline Risk: Locally appropriate sea-level rise scenarios and planning time frames were selected. High-water level depths were established based upon different scenarios and predicted changes in extreme events. The land, property, and infrastructure exposed to future flooding was assessed including both the primary and secondary impacts to those assets if no action is taken. Impacts to beaches also were assessed as a community asset. A monetary value was developed to determine the total economic costs of sea-level rise for each city.
- Assess Adaptation Strategies: Various adaptation strategies for reducing or protecting against sea-level rise risks were identified and evaluated based upon their effectiveness at reducing risks.
- Calculate Costs and Benefits: The costs to implement each adaptation strategy were estimated, the benefits in terms of damages prevented for each action scenario were estimated, and the negative impacts from different action scenarios were also accounted for (i.e., seawalls could negatively affect beach tourism)
- Inform Decisionmaking: The total benefits of each action scenario were estimated, capital and maintenance costs were considered, and benefit cost ratios were developed to inform decisionmaking.
The report lists the assumptions, data sources, and methods that were used for valuing benefits and costs. A sensitivity analysis was conducted to assess the study’s assumptions related to the effectiveness/protectiveness of each action scenario, discount rate selected (a discount rate of 1 to 3 percent was used), loss of tax revenues.
All adaptation strategies assessed in the study had a benefit-cost ratio of greater than 1, with some scenarios showing a high return on investment. For example, an assessment of beach nourishment and groins for the City of Carlsbad (Action Scenario 1) showed that $1 spent on adaptation would return $72.88 in benefits.
Lessons learned are included which describe how the authors modified the NOAA framework to meet local needs and to provide more specific guidance based upon local characteristics. Consideration of site-specific information was essential for not only evaluating risk but also to ensure the accuracy of cost estimates for construction and maintenance of different adaptation strategies. GIS and on-the-ground inspections helped the authors groundtruth and test the accuracy of their vulnerability analyses.
The San Diego Regional Climate Collaborative prepared this report under a grant from the U.S. Department of Commerce under NOAA's Coastal Resilience grant program. It was developed as a part of a larger initiative of the San Diego Collaborative to support coastal resilience among local governments and other agencies and stakeholders in the region.
Publication Date: June 2017
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