Available Now: Hawai’i Sea Level Rise Vulnerability & Adaptation Report

The Hawai’i Sea Level Rise Vulnerability & Adaptation Report (2017) is available now! This important report illustrates why we need better long-term planning on Maui – no more building in the tsunami evacuation and coastal flood zones.

Excerpt from Maui section of the report (pages 90-91):

The Island of Maui, known as “The Valley Isle,” is the largest and most populous island in Maui County. Maui boasts a varied geography with coastal communities and mountainous areas in West Maui, small towns and agricultural communities in Upcountry and East Maui, and the more urbanized areas of Central Maui (County of Maui 2012). With 148,403 residents (State of Hawai’i 2015), the Island of Maui accounts for 10.6% of the State’s population. Since the 1970s, Maui has experienced significant growth in both resident and visitor populations. A near tripling of Maui’s population over the last 50 years, coupled with a growing tourism industry—over 2.6 million visitors came to Maui in 2016 (State of Hawai’i 2016) —has placed ever increasing demands on natural resources, critical infrastructure, and basic services.

Key Take Aways

  • Over the next 30 to 70 years, homes and businesses located near the shoreline will be severely impacted by sea level rise. Nearly 300 structures would be chronically flooded with 3.2 feet of sea level rise.
  • Of the 3,130 acres of land located within the SLR-XA, approximately a third of those lands are designated for urban land uses.
  • With 3.2 feet of sea level rise, more than 11 miles of major coastal roads would become impassible jeopardizing critical access to and from many communities.
  • Maui has lost more than 4 miles of beaches to coastal erosion fronting seawalls and other shoreline armoring. Many more miles of beach could be lost with sea level rise, if widespread armoring is allowed.

 

A more detailed economic loss analysis is needed of Maui’s critical infrastructure, including harbor facilities, airport facilities, sewage treatment plants, and roads. State and Counties should consider potential benefits in terms of long-term cost savings from implementing sea level rise adaption measures now (e.g., major flood proofing or relocation) compared to the cost of maintaining and repairing chronically threatened public infrastructure over the next 30 to 70 years.

This section provides a picture of the future of the sland of Maui with sea level rise and the potential impacts from chronic flooding. The results are based on modeling coastal flooding with sea level rise due to passive flooding, annual high wave flooding, and coastal erosion in the SLR-XA with up to 3.2 feet of sea level rise, and depicts flood hazards that may occur in the mid- to latter-half of this century. This timeframe is within the expected lifespan of most new construction and much of our existing development. It should be noted that sea level rise projections greater than 3.2 feet are “physically plausible” by the end of the century, based on the latest climate science (Sweet et al. 2017, Le Bars, Drijfhout, and de Vries 2017). Vulnerability to 1.1 feet of sea level rise in the SLR-XA is used to approximate current or near-term exposure to coastal hazards and sea level rise. Vulnerability is assessed in terms of potential impacts to land use, people, property, cultural and natural resources, and critical infrastructure (only land and structures are monetized, not infrastructure).

The reader is urged to exercise caution in interpreting the results, which could be to a greater or lesser extent depending on actual observed future sea level rise, technological innovations in climate change mitigation and adaptation, unknown economic variables, as well as future societal choices which cannot be known today. Further, as not all parts of the island can be shown in detail, the reader should also visit the Hawaiʻi Sea Level Rise Viewer to explore the full extent of the vulnerability maps for each island.

Potential Impacts in the Sea Level Rise Exposure Area

The SLR-XA depicts the area of potential chronic flooding from the combined exposure to passive flooding, annual high wave flooding, and coastal erosion with sea level rise. With 3.2 feet of sea level rise, low-lying coastal areas around the island within the SLR-XA would become chronically flooded within the mid- to latter-half of this century (Figure 53). This land will become submerged as a result of coastal erosion, coastal flooding from tides and waves, or become new wetlands behind the shoreline from rising water tables and reduced drainage. Approximately 3,130 acres of land on Maui is estimated to be located in the SLR-XA, with one third of that located in the Urban District.

Towns such as Waihe‘e, Hana, Lāhainā, Kīhei, and others, that are vulnerable to the effects of sea level rise are shown in Figure 54. Waihe‘e is a small rural town located on the northwest side of the island where portions of the Waihe‘e Coastal Dune and Wetlands Refuge would be permanently flooded with 3.2 feet of sea level rise. In the town of Hana, higher sea levels would form new wetlands that would impact rural homeowners. Lāhainā, the former capital of the State of Hawaiʻi and an important seaport, is an urban settlement in West Maui backed by agricultural lands and the West Maui Mountains. With 3.2 feet of sea level rise, Lāhainā’s historic district would be exposed to chronic flooding, along with portions of the town itself which is West Maui’s visitor, service, commercial and residential center. Kīhei is the residential and commercial center of Southwest Maui. It has been identified as a planned growth area in the County due to the existing opportunities to expand outward from current settlement areas (County of Maui 2010). However, many areas in Kīhei may succumb to flooding from sea level rise. Thoughtful planning about where and how this expansion could occur is important to ensure new development is resilient to sea level rise.

Over time, as sea level continues to rise, low-lying, populated coastal communities such as Spreckelsville would experience increased frequency and severity of flooding, ultimately making some areas of the coast impassible or uninhabitable (Figure 55). Decisions about where to use coastal armoring and when to retreat will need to be made carefully. It should be noted that seawalls may not be effective at preventing flooding with sea level rise in many low-lying areas as rising groundwater can infiltrate through porous geology. While specific responses to sea level rise would need to be place-based, larger regional issues should also be considered, such as whether to armor in place or whether to relocate roads and other critical infrastructure inland. In the case of Spreckelsville and similar coastal communities, there may be opportunities for managed retreat inland, as there are ample vacant lands immediately mauka (landward) and outside of the SLR-XA. However, as discussed in the Recommendations Chapter of this Report (Chapter 5), and as with other populated coastal areas with adjacent vacant lands, large-scale boundary amendments should be predicated on appropriate state policies and guidelines (e.g., within Chapter 205, State Land Use Act) to provide the supportive legal basis for major land use changes.

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