Rapid remote volcanic ashfall impact assessment for the 2022 eruption of Hunga volcano, Tonga: a bespoke approach and lessons identified

When disasters occur, rapid impact assessments are required to prioritise response actions, support in-country efforts and
inform the mobilisation of aid. The 15 January 2022 eruption of Hunga volcano, Tonga, and the resulting atmospheric
shockwave, ashfall, underwater mass disturbance and tsunami, caused substantial impacts across the Kingdom of Tonga.
Volcanic impacts on the scale observed after the eruption are rare, necessitating a reliance on international advice and assis-
tance. The situation was complicated by the loss of Tonga’s international submarine fibreoptic cable (causing a complete
loss of communications for approximately 20 days) along with border closures due to the COVID-19 pandemic. A need
emerged for a rapid remote volcanic impact assessment and provision of specialist advice to help inform the response of
international partners. Here we present a novel methodology for conducting rapid remote volcanic ashfall impact assess-
ments, conducted over a 10-day period following the eruption. We used three different hazard models for ashfall thickness
across the main island of Tongatapu and available asset information and vulnerability functions for buildings, agriculture,
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electricity networks, water supply and roads, to provide initial estimates of losses due to ashfall from the 15 January erup-
tion. For buildings, we estimated losses both as total losses and as percentages of the total replacement cost of buildings
on Tongatapu. For agriculture, we made probabilistic estimates of production losses for three different crop classes. For
ashfall clean-up, we estimated ranges of ashfall volumes requiring clean-up from road surfaces and roofs. For water supply,
electricity networks and roads, our analysis was limited to assessing the exposure of important assets to ashfall, as we had
insufficient information on system configurations to take the analysis further. Key constraints on our analysis were the limited
nature of critical infrastructure asset inventories and the lack of volcanic vulnerability models for tropical regions including
Pacific Island nations. Key steps towards iteratively improving rapid remote impact assessments will include developing
vulnerability functions for tropical environments as well as ground-truthing estimated losses from remote approaches against
in-person impact assessment campaigns.