Preprints
https://doi.org/10.5194/nhess-2021-181
https://doi.org/10.5194/nhess-2021-181

  07 Jul 2021

07 Jul 2021

Review status: this preprint is currently under review for the journal NHESS.

Generating reliable estimates of tropical cyclone induced coastal hazards along the Bay of Bengal for current and future climates using synthetic tracks

Tim Willem Bart Leijnse1, Alessio Giardino1, Kees Nederhoff2, and Sofia Caires1 Tim Willem Bart Leijnse et al.
  • 1Deltares, Delft, 2600MH, The Netherlands
  • 2Deltares USA, 8601 Georgia Ave., Silver Spring, MD 20910, USA

Abstract. Deriving reliable estimates of design water levels and wave conditions resulting from tropical cyclones is a challenging problem of high relevance for, among others, coastal and offshore engineering projects and risk assessment studies. Tropical cyclone geometry and wind speeds have been recorded for the past few decades only, therefore resulting in poorly reliable estimates of the extremes, especially at regions characterized by a low number of past tropical cyclone events. In this paper, this challenge is overcome by using synthetic tropical cyclone tracks and wind fields generated by the open source tool TCWiSE (Tropical Cyclone Wind Statistical Estimation), to create thousands of realizations representative for 1,000 years of tropical cyclone activity for the Bay of Bengal. Each of these realizations is used to force coupled storm surge and wave simulations by means of the processed-based Delft3D Flexible Mesh Suite. It is shown that the use of synthetic tracks provides reliable estimates of the statistics of the first-order hazard (i.e. wind speed) compared to the statistics derived for historical tropical cyclones. Based on estimated wind fields, second-order hazards (i.e. storm surge and waves) are computed. The estimates of the extreme values derived for wind speed, wave height and storm surge are shown to converge within the 1,000 years of simulated cyclone tracks. Comparing second-order hazard estimates based on historical and synthetic tracks show that, for this case study, the use of historical tracks (a deterministic approach) leads to an underestimation of the mean computed storm surge up to −30 %. Differences between the use of synthetic versus historical tracks are characterized by a large spatial variability along the Bay of Bengal, where regions with a lower probability of occurrence of tropical cyclones show the largest difference in predicted storm surge and wave heights. In addition, the use of historical tracks leads to much larger uncertainty bands in the estimation of both storm surges and wave heights, with confidence intervals being +80 % larger compared to those estimated by using synthetic tracks (probabilistic approach). Based on the same tropical cyclone realizations, the effect that changes in tropical cyclone frequency and intensity, possibly resulting from climate change, may have on modelled storm surge and wave heights were computed. An increase in tropical cyclone frequency of +25.6 % and wind intensity of +1.6 %, based on literature values, could result in an increase of storm surge and wave heights of +11 % and +9 % respectively. This suggest that climate change could increase tropical cyclone induced coastal hazards more than just the actual increase in maximum wind speeds.

Tim Willem Bart Leijnse et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2021-181', Anonymous Referee #1, 08 Jul 2021
  • RC2: 'Comment on nhess-2021-181', Anonymous Referee #2, 21 Oct 2021

Tim Willem Bart Leijnse et al.

Tim Willem Bart Leijnse et al.

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Short summary
Deriving reliable estimates of design conditions resulting from tropical cyclones is a challenging problem of high relevance for coastal engineering. In this paper, the challenge of having few historical observations is overcome by using TCWiSE to create thousands of synthetic realizations, representative for 1,000 years of tropical cyclone activity for the Bay of Bengal. It is shown that the use of synthetic tracks provides more reliable estimates of wind speeds, storm surge and waves.
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