City and County of Honolulu, Hawaii Multi-Hazard Pre-Disaster Mitigation Plan

In 2019, the City and County of Honolulu on the Hawaiian island of Oahu adopted an updated Multi-Hazard Pre-Disaster Mitigation Plan approved by the Federal Emergency Management Agency (FEMA). The dual purposes of the plan are to protect people and structures from damage, and to minimize the city and county’s disaster response and recovery costs. The plan, prepared by the Department of Emergency Management, addresses the relationship among various types of hazards, evaluates the effects of climate change, and prioritizes mitigation policies, actions, and projects. The 2019 plan is a comprehensive update of the city and county’s 2012 plan, and includes a new chapter specifically focused on climate change effects. The plan identifies 13 hazards, including climate change effects, and corresponding actions the city and county may take to minimize future risks. For example, managed retreat has been proposed as a potential adaptation strategy to reduce risks from sea-level rise, flooding, and coastal erosion to people, ecosystems, homes, and infrastructure along the coast. As a result of this effort, the City and County of Honolulu will aim to integrate this plan with other local land-use and zoning plans and policies to factor hazard mitigation into future development decisions. 

The report is organized according to 13 hazards:

  • Climate change effects
  • Coastal erosion
  • Strong winds (not associated with cyclones)
  • Tropical cyclones
  • Floods 
  • Tsunamis
  • Earthquakes
  • Landslides and rockfalls
  • Droughts
  • Wildfire
  • Hazardous materials
  • Dam failures
  • Vog (smog or haze containing volcanic dust and gases
  • Status of emergency shelters

For each hazard, the plan summarizes anticipated impacts for Honolulu and potential adaptation and risk mitigation strategies that could be taken by the government. Chapter 4 on climate change effects first describes climate impacts on the island’s coast, including gradual sea-level rise and increasing rates of beach erosion and groundwater rise, among others. According to the State of Hawaii’s Sea-Level Rise Vulnerability and Adaptation Report, Oahu is particularly vulnerable to rising seas. Under one scenario considered, two feet of sea-level rise would inundate parts of Oahu containing the airport and other important urban areas. 

The chapter then discusses potential climate change adaptation and risk mitigation strategies. Notably, some of the proposed strategies relate to managed retreat to relocate or restrict development in high hazard areas: 

  • Relocate critical infrastructure, like roads, in eroding coastal regions.
  • Develop floodplain maps for Honolulu that exceed FEMA requirements for the 100-year or one-percent chance floodplain by factoring sea-level rise, increasing precipitation, and storm surge into designating the 100- and 500-year floodplains. These maps could ultimately be used to inform land-use and zoning ordinances in Honolulu to limit or restrict future development within floodplains. 
  • Adopt setbacks for new construction or additions based on 25 feet plus 50 years of expected shoreline erosion. Setbacks can keep development away from eroding shorelines. 
  • Establish a “Coastal Construction Control Zone” to incorporate sea-level rise and coastal erosion into the siting and design of larger scale developments to ensure they will not be located in vulnerable locations.  

Through its plan, Honolulu is proactively identifying managed retreat among the range of adaptation options the government can consider for purposes of protecting people, ecosystems, structures, and infrastructure in coastal areas. Managed retreat could potentially be incorporated into plans and policies as a part of the city and county’s efforts to integrate the Multi-Hazard Pre-Disaster Mitigation Plan with other local efforts (Chapter 3.9.1). 

In addition, Honolulu’s Multi-Hazard Pre-Disaster Mitigation Plan provides an example of how state and local plans can be integrated. In 2018, the Hawaii Emergency Management Agency released an update to the state’s Hazard Mitigation Plan. Similar to Honolulu’s Multi-Hazard Pre-Disaster Mitigation Plan, the state’s Hazard Mitigation Plan also includes managed retreat as potential adaptation strategies in its mitigation action plan:

  • Prepare a report on Assessing the Feasibility and Implications of Managed Retreat Strategies for Vulnerable Coastal Areas in Hawaii (released in 2019 and funded by the National Oceanic and Atmospheric Administration) (Mitigation Action #2018-047).
  • Pilot managed retreat projects and nature-based solutions for threatened infrastructure throughout Hawaii (not implemented as of 2019, but may potentially be funded by the National Oceanic and Atmospheric Administration) (Mitigation Action #2018-048).

Honolulu’s Multi-Hazard Pre-Disaster Mitigation Plan is building on the state’s Hazard Mitigation Plan to ensure that potential managed retreat projects for infrastructure and new development in Honolulu can be aligned with state objectives, and leverage federal funding opportunities (e.g., for hazard mitigation, coastal management). Moreover, in 2019, the state’s Office of Planning, Coastal Zone Management Program released a feasibility study on managed retreat, which was identified in the state’s hazard mitigation plan. This work across the state’s hazard mitigation and coastal management agencies further exemplifies cross-state and state-local coordination. 

Honolulu’s Multi-Hazard Pre-Disaster Mitigation Plan was developed through significant engagement with city and county representatives (e.g., the mayor, City Council, city’s Office of Climate Change, Sustainability, and Resiliency, the Honolulu Climate Change Commission), community organizations, and the state (e.g., Hawaii Emergency Management Agency, Hawaii Department of Land and Natural Resources), and federal government agencies (e.g., National Oceanic and Atmospheric Administration).


Publication Date: 2019

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