Projected Characteristic Changes of a Typical Tropical Cyclone under Climate Change in the South West Indian Ocean

Callum Thompson,Joris Pianezze,Christelle Barthe,Soline Bielli,Pierre Tulet

doi:10.3390/atmos12020232

Abstract

During 2 January 2014, Cyclone Bejisa passed near La Réunion in the southwestern Indian Ocean, bringing wind speeds of 41 m s−1, an ocean swell of 7 m, and rainfall accumulations of 1025 mm over 48 h. As a typical cyclone to impact La Réunion, we investigate how the characteristics of this cyclone could change in response to future warming via high-resolution, atmosphere–ocean coupled simulations of Bejisa-like cyclones in historical and future environments. Future environments are constructed using the pseudo global warming method whereby perturbations are added to historical analyses from six Coupled Model Intercomparison Project 5 (CMIP5) climate models. These models follow the Intergovernmental Panel for Climate Change’s (IPCC) Representative Concentration Pathways (RCP) RCP8.5 emissions scenario and project ocean surface warming of 1.1–4.2 °C by 2100. Under these conditions, we find that future Bejisa-like cyclones are 6.5% more intense on average and reach their lifetime maximum intensity 2 degrees further poleward. Additionally, future cyclones produce heavier rainfall, with a 33.8% average increase in the median rainrate, and are 9.2% smaller, as measured by the radius of 17.5 m s−1 winds. Furthermore, when surface wind output is used to run an ocean wave model in post, we find a 4.6% increase in the significant wave height.

Highlights

During 2 January 2014, Cyclone Bejisa passed near La Réunion in the southwestern Indian Ocean, bringing wind speeds of 41 m s−1, an ocean swell of 7 m, and rainfall accumulations of 1025 mm over 48 h [1]
For La Réunion, rainfall and wave height changes are important as its volcanic landscape enhances orographic precipitation, while the approximate 866,000 population largely resides within 10 miles of the coast
Trajectories of all simulated cyclones are determined from tracking the minimum mean sea-level pressure (MSLP) from 3-hourly Meso-NH output

Summary

Introduction

During 2 January 2014, Cyclone Bejisa passed near La Réunion in the southwestern Indian Ocean, bringing wind speeds of 41 m s−1, an ocean swell of 7 m, and rainfall accumulations of 1025 mm over 48 h [1]. Given recent indications of increasing TC intensity for this basin [2,3,4], and the growing confidence for this trend to continue over the coming century [5,6], the question arises as to how damaging a Bejisa-like cyclone could be in the future Addressing such a question depends on projecting changes in TC characteristics, such as intensity, rainfall, size, and the associated ocean wave induced by high winds. Strong winds and rainfall accounts for most TC-related damages and fatalities, with wave height contributing towards infrastructure damage in the wider basin [7] Projecting how these cyclone characteristics could change in a warmer climate is vital in projecting future cyclonic impact

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Conclusion