Moving Earth (not heaven): A novel approach to tropical cyclone impact modelling, demonstrated for New Zealand

Abstract

Some of the historically highest-impact weather events to affect New Zealand have been caused by ex-tropical cyclones (ex-TCs) which have had significant direct and indirect adverse effects. The weather theme of a New Zealand government funded research programme known as the Resilience to Nature’s Challenges (RNC2) aims to create physical datasets of high-impact, yet credible, extreme weather events not previously available to researchers and end-users. This paper focusses on the potential scenarios of a major ex-TC impacting Auckland and surrounding areas in the north of New Zealand. Highly-detailed, meteorologically consistent data of such events are produced by relocating the New Zealand land mass into the path of historical ex-TC cases, using convection permitting simulations of the Met Office Unified Model. We illustrate the applicability of this method over simpler (non-consistent) methods, and show for ex-TC Cook (April 2017) what wind strength and precipitation totals would have been for a track just slightly to the west of reality. Finally, we illustrate how sub-kilometre simulations nested within the main simulation can add significant additional detail at the city scale, and show how simple modifications, for example raising the sea-surface temperature, can illustrate how events may change in future. Such scenarios may prove invaluable in designing future infrastructure and planning for such an event.

Keywords

• Tropical cyclones
• Risk modelling
• High-resolution simulations
• Unified model