HDOT Climate Resilience Action Plan | May 2021

EXAMPLES OF PAST EVENTS Past examples of extreme weather disruptions serve as a good reference to the type of impacts that could occur in the future, especially along the shoreline or in areas of lava flow. A record of past events is presented below as a reference. However, as noted earlier, it should be kept in mind that past events are not fully representative of the events or conditions that may be brought about by changing climate conditions. COASTAL EROSION AND SHORELINE CHANGE Coastal erosion and shoreline change are some of the most visible impacts associated with changing climatic conditions in Hawai‘i, especially when coupled with coastal development and shoreline hardening. It is estimated that 70% of the State’s beaches have a trend of chronic erosion (Fletcher et al 2012). Such incidents have been documented for years at multiple locations (Dalton 2020, University of Hawai‘i’ 2016). Sections along the Kamehameha Highway, a vital two-lane highway in Hau‘ula, have been affected by coastal erosion along O‘ahu’s Windward coast. This highway has experienced service disruptions at multiple locations due to erosion, most notably Ka‘a‘awa to the southeast of Hau‘ula (Figure 3) and the Laniākea area farther northwest on the North Shore. In 2015, the governor signed an Emergency Proclamation authorizing emergency repairs of the roadway at Ka‘a‘awa. More recently, HDOT earmarked a project to move the highway farther from the shoreline at Laniākea, and this stretch of highway has been identified as a top-20 priority site (Francis et al. 2019). STORM SURGE AND HIGH WINDS Storm surge resulting from tropical storms and hurricanes can exacerbate coastal erosion and cause serious damage to roads. Hurricane Iwa (1982), which passed just north of Ni‘ihau and Kaua‘i as a Category 2 tropical storm, and Hurricane Iniki (1992), which made landfall as a Category 4 storm on the southern shore of Kaua‘i, seriously damaged many parts of the State (Robertson 2015). More recently, Hurricane Iselle (2014), which made landfall as a tropical storm on the southeastern coast of Hawai‘i Island (Big Island), caused power outages and much damage to communities and supporting infrastructure. Category 5 Hurricane Lane (2018) weakened just as it approached the Hawaiian Islands and avoided a direct hit on the State. The Hawaiian Islands will likely experience more frequent tropical storms as ocean temperatures rise and hurricane tracks shift more northerly (Yamaguchi 2019).

Adopt a Proactive Approach

Invest in Inventory Data to Better Define Risks

Bound Future Conditions to Improve Understanding

Invest in Additional Analysis for At-Risk Facilities

Refine Investment Needs

Take Action in Areas with Highest Concerns

Figure 2 Risk Mitigation Approach

In addition, the strong winds associated with hurricanes cause portions of buildings, telephone poles and trees/ foliage to fall and block roads. In many recent storm events, emergency crews could not reach damaged areas until the roads were cleared. INTENSIVE PRECIPITATION, LANDSLIDES, ROCK- FALLS, DEBRIS FLOWS, AND INLAND FLOODING Precipitation in the mauka and makai areas can cause flooding, landslides, and other geotechnical hazard events such as rockfalls and debris flows. In April 2018, heavy precipitation damaged Kūhiō Highway on Kaua‘i (Figure 4), and traffic was severely restricted for about a year while the roadway was reconstructed and stabilized. Other disruption examples occurred in a nearby area of Kalihiwai in northeast Kaua‘i. In separate occasions, in 2012 and 2018, a Kūhiō Highway stream crossing was re-routed because of high water flow. In February 2019, heavy precipitation caused multiple debris flows along the Pali Highway on O‘ahu. This event caused the closure of one of the entrances to the highway’s four tunnels, temporarily severing roadway

Figure 3 Kamehameha Highway Repairs at Ka‘a‘awa, O‘ahu

12 HAWAI I HIGHWAYS C L I MAT E ADAP TAT I ON ACT I ON P L AN