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

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.

The Effect of Atmosphere-Ocean Coupling on the Structure and Intensity of Tropical Cyclone Bejisa in the Southwest Indian Ocean

“…In this section, we recall some key features of tropical cyclone TC Bejisa, which detailed description can be found in Pianezze et al [26]. TC Bejisa is representative of the storms that regularly affect Reunion Island and has been chosen for its relatively common meridian track, average intensity and speed of displacement [27]. In this study we focus on the period between 1 January 00 UTC and 2 January 12 UTC, which corresponds to the period it passed to the closest to Reunion Island.…”

Impact of Tropical Cyclones on Inhabited Areas of the SWIO Basin at Present and Future Horizons. Part 1: Overview and Observing Component of the Research Project RENOVRISK-CYCLONE

“…This strategy relies on the exploitation of unprecedented high-resolution global climate simulations [32], as well as of mesoscale coupled simulations to estimate the impact of climate change on the intensity, behavior, and consequences of TCs at the scale of a given territory. Examples of results obtained from such high-resolution model runs are discussed in [33,67] (both in this Special Issue).…”

Impact of Tropical Cyclones on Inhabited Areas of the SWIO Basin at Present and Future Horizons. Part 2: Modeling Component of the Research Program RENOVRISK-CYCLONE

“…They showed that using a 1D coupling (Meso-NH coupled to a 1D ocean mixed layer model) does not enable to reproduce the intensity and structure of surface ocean cooling compared to composite observations, while a 3D coupled model (Meso-NH coupled to the 3D NEMO model) does. Finally, an ocean-atmosphere configuration with km-scale grid spacing was implemented to investigate how the characteristics of a typical TC like Bejisa would evolve in the context of climate change [67]. The pseudo global warming method was used to construct future environments: perturbations computed from six Coupled Model Intercomparison Project 5 (CMIP5) climate models were added to historical analyses from ECMWF.…”

“…One of the goals of the climate component of RNR-CYC was thus to evaluate the future evolution of TC activity in the SWIO. While high-resolution simulations performed with global models are used to anticipate the global evolution of the TC activity [13], a pseudo global warming procedure is implemented in the coupled OWA model described in Section 2 to evaluate the modifications of the TC structure and impacts in a modified oceanic and atmospheric environment [67].…”

“…In addition, in the frame of RNR-CYC, Thompson et al [67] used a pseudo global warming method to estimate the projected change of a Bejisa-like TC in the second half of the century with a projected SST warming of 1.1-4.2 • C (RCP 8.5 scenario). Such a TC has the potential to be more intense (+6.5% on average), to reach its LMI 2 • further poleward, and with a 33.8% increase of the median rainrate.…”