Variations in extreme wave events near a South Pacific Island under global warming: case study of Tropical Cyclone Tomas

Kenji Taniguchi,Yoshimitsu Tajima

doi:10.1186/s40645-020-0321-y

Abstract

The intensification of tropical cyclones (TCs) and wind-induced ocean waves is expected to be amplified under global warming conditions. In 2010, strong TC Tomas approached the Fiji Islands and caused severe damage. Here, an ensemble simulation technique is combined with a pseudo-global warming (PGW) method to investigate future variations in TCs and wind-induced ocean waves. Ensemble PGW simulations were implemented using the weather research and forecasting (WRF) model with five different future projections. Hindcast and PGW simulations showed similar tracks of Tomas. In four PGW simulations, the central pressures of the simulated TCs decreased. Enhanced near-surface wind was recognized in three PGW simulations around the Fiji main island (Viti Levu). In the other two future simulations, the surface wind speed was weaker than the one in the present climate because of the slight eastward shift in the track and delayed development of the TC. WaveWatchIII (WW3) was applied for offshore wave simulations forced by the wind field obtained by WRF simulation results. In three future simulations, a clear increase in the maximum significant wave height (Hs) was found on the southeastern coast of Viti Levu. One future simulation yielded almost the same offshore wave characteristics as those under the present climate. In another future simulation, the ensemble mean Hs was as high as that in the present climate, but extremely large Hs values were found in several ensemble members. Future simulations using multiple global climate model (GCM) projections showed possible variations in TCs and wind-induced ocean waves which is useful for the risk assessment of various hazards.

Highlights

Ocean surface waves are generated by local surface wind; wave characteristics are highly affected by variations in atmospheric conditions caused by climate change
The pseudo-global warming (PGW) conditions consist of the National Centers for Environmental Prediction (NCEP) NCEP Final Operational Global Analysis (FNL) data and future climate projections from five different global climate model (GCM) that were developed for Couples Model Intercomparison Project Phase 5 (CMIP5) (Taylor et al 2012)
These results indicate that the development of the Tropical cyclone (TC) delays PGW-2 and that the wind speed is weaker around Fiji

Summary

Introduction

Ocean surface waves are generated by local surface wind; wave characteristics are highly affected by variations in atmospheric conditions caused by climate change. Data This study uses the National Centers for Environmental Prediction (NCEP) FNL (Final) Operational Global Analysis (NCEP FNL) for the initial and boundary conditions of the hindcast weather simulation of TC Tomas and the base state of the PGW conditions. The PGW conditions consist of the NCEP FNL data and future climate projections from five different GCMs that were developed for CMIP5 (Taylor et al 2012). Extreme weather events in a specific area (e.g., around the main island of Fiji, Viti Levu) were investigated by applying the ensemble simulation technique (LSP method described later) to obtain several simulation results. To compare the variations in the characteristics of typhoons and ocean waves in a specific region under different climate conditions, the results of the ensemble simulations must have similar meteorological spatial distributions. Wave simulations The third-generation spectral wave model WaveWatchIII (WW3; Tolman 2009) was used for the wave

MIROC5

Results and discussion

Conclusions