Evaluation of storm surge risk: A case study from Rarotonga, Cook Islands

Abstract

This study reports on a preliminary assessment of storm surge risk from tropical cyclones at Rarotonga, Cook Islands. Analysis of a 175-year record of cyclones from the Cook Islands indicates minimum annual probabilities of 16% for storm surges and 5% for major storm surge impacts at Rarotonga. Storm surges have historically inundated areas of the coastal lowland where virtually all human activities and infrastructure are currently located. The impacts of such events have been particularly severe in the Cook Islands' capital of Avarua and adjacent communities on the north coast of Rarotonga. Detailed infrastructure mapping combined with analysis of historic storm surge impacts and cyclone tracks in the vicinity of Rarotonga indicates that the storm surge risk is greatest along the north coast where the majority of the Cook Islands' government functions and commercial, industrial, transportation and communication infrastructure is located. Damage to this infrastructure at the shoreline can have serious repercussions throughout the Cook Islands. Any efforts to increase the country's resilience to such impacts must be undertaken within the larger goal of adaptation to future climate changes and rising sea levels. The greatest risk presently to human life arises from many cyclone safety centres in locations where they are exposed to storm surges or flooding. A top priority should be relocation of these shelters to safer locations further inland so that they can provide suitable shelter from storm surges and flooding as well as tsunamis, taking into account other hazards presented by Rarotonga's rugged topography.