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Increasing frequency of extremely severe cyclonic storms over the Arabian Sea


In 2014 and 2015, post-monsoon extremely severe cyclonic storms (ESCS)—defined by the WMO as tropical storms with lifetime maximum winds greater than 46 m s1—were first observed over the Arabian Sea (ARB), causing widespread damage. However, it is unknown to what extent this abrupt increase in post-monsoon ESCSs can be linked to anthropogenic warming, natural variability, or stochastic behaviour. Here, using a suite of high-resolution global coupled model experiments that accurately simulate the climatological distribution of ESCSs, we show that anthropogenic forcing has likely increased the probability of late-season ECSCs occurring in the ARB since the preindustrial era. However, the specific timing of observed late-season ESCSs in 2014 and 2015 was likely due to stochastic processes. It is further shown that natural variability played a minimal role in the observed increase of ESCSs. Thus, continued anthropogenic forcing will further amplify the risk of cyclones in the ARB, with corresponding socio-economic implications.

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The authors thank T. L. Delworth and L. Krishnamurthy for their suggestions and comments. H.M. appreciates P.-C. Hsu for her editorial service support. This report was prepared by H.M. under award NA14OAR4830101 from the National Oceanic and Atmospheric Administration (NOAA), US Department of Commerce. The statements, findings, conclusions and recommendations are those of the authors and do not necessarily reflect the views of the NOAA or the US Department of Commerce.

Author information

H.M. designed the study, carried out the experiments and analysed the results. G.A.V. and S.W. carried out the experiments and made comments on the manuscript.

Correspondence to Hiroyuki Murakami.

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Supplementary Information Supplementary Table 1, Supplementary Figures 1–12, Supplementary Reference

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Further reading

Fig. 1: Observed ESCSs.
Fig. 2: Projected changes in the seasonal mean density of ESCSs.
Fig. 3: Projected probability of exceedance of ESCSs over the ARB during October–December for each experiment.
Fig. 4: Projected changes in seasonal mean SST and V s.