HDOT Climate Resilience Action Plan | May 2021

Figure 4 2018 Landslides on Kūhiō Highway, North Shore Kaua‘i

connectivity between the major residential communities on the Windward side of the island and the major employment center in Downtown Honolulu on the other side of the mountain. Traffic operations did not return to normal for several months. GROUNDWATER INUNDATION The degradation of a road foundation by rising groundwater seriously impacts roadway integrity that is less visible to the traveling public than other natural hazards, requiring increased maintenance or premature replacement. Rising groundwater also limits the capacity of the land to absorb rainfall, increasing localized flooding. This groundwater inundation effect, sometimes identified first through recurrent high-tide flooding in low-lying areas, is already occurring. The most notable examples on the Island of O‘ahu have occurred in the Māpunapuna neighborhood mauka of the Nimitz Highway in the Honolulu International Airport area and in the Kapi‘olani Boulevard area mauka of Ala Moana Shopping Center. The flooding of the Mapunapuna area caused intrusion/backflow of seawater. At one time, this area had many fishponds, which were later filled in; intruding seawater has reclaimed some of the low areas. Low-lying coastal highway areas experiencing repeated coastal erosion, such as areas along Kamehameha Highway on O‘ahu, are also susceptible to groundwater inundation or a gradual transition to wetlands that may not be immediately and readily observable (Habel et al 2020). TSUNAMIS Tsunamis generated by earthquakes remain a constant, albeit infrequent, threat to Hawai‘i. Although infrequent, the consequences associated with tsunamis are significant. Two of the most famous and deadly tsunami events occurred in Hilo Bay on the Big Island in 1946 and 1960, completely reshaping the social and economic structure of Hilo, in addition to changing its land use and development patterns (Pacific Tsunami Museum 2020, State of Hawai‘i 2019). Tsunami wave forces have the capacity to damage bridges and coastal roadways, eliminating access to communities.

WILDFIRES Climate change is expected to result in some areas experiencing heavier precipitation, while others might become more prone to drier conditions, with each condition resulting in a greater risk of nature- and human-caused wildfires. In areas of heavier precipitation, vegetation growth encouraged by precipitation could act as fuel for future wildfires. In 2018, there were 627 wildfires in Hawai‘i, which burned 32,386 acres of land (Pacific Fire Exchange. 2019). Fire ignitions tend to occur on the drier leeward side of islands, and they are most associated with population centers and the presence of roads and vehicles, which tend to contribute to the ignition of fires (Trauernicht 2016, Pacific Fire Exchange 2016). LAVA FLOW Volcanic eruption and lava flows are an infrequent but potentially devastating hazard in the State. Hawai‘i Island (Big Island) is most prone to this disruption, with K ī lauea Volcano having erupted 34 times since 1952 (USGS 2020). In the most recent 2018 eruption, which lasted approximately 4 months (USGS 2019a), lava flows disrupted local roadways in the Puna area and cut off access to critical community assets such as schools, local commerce, and the only boat ramp in Puna. No State-owned roads were directly affected by the eruption, but county roads were affected. However, State highways did experience cracks in the pavement due to earthquake-related underground movement of lava and needed repair. PAST REPAIR SITES Figure 5 shows the locations of emergency or related HDOT projects from 1997 to January 2019 resulting from natural hazard impacts. These repair projects included both emergency and non-emergency actions needed on roads affected by weather- related events (HDOT 2019b). The repair projects typically resulted from severe storms, landslides, flooding, bridge/ drainage, and shoreline erosion. Roughly 60 miles of the total 971 miles of the State’s highway network are represented on this list of repair projects during this period. Also mapped are landslides co-located with HDOT highway assets and documented in the USGS National Landslide Inventory (USGS 2019b).

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