26 Sep 2022
 | 26 Sep 2022
Status: this preprint is currently under review for the journal WCD.

Future changes in the mean and variability of extreme rainfall indices over the Guinea Coast and role of the Atlantic equatorial mode

Koffi Worou, Thierry Fichefet, and Hugues Goosse

Abstract. The occurrence of climate extremes could have dramatic impacts on various sectors such as agriculture, water supply, and energy production. Over the last decades, less frequent and more intense rainfalls have been observed in the coastal areas of West Africa (the Guinea Coast). Part of this variability in the extreme rainfalls can be related to the Atlantic equatorial mode (AEM) whose positive phases are associated with an enhancement of the mean rainfall over the Guinea Coast and an increase in the intensity and frequency of rainfall events. The climate models that participate in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) simulate reasonably well the rainfall extremes over the Guinea Coast and West Africa. However, less attention has been paid to the evaluation of the modelled rainfall extremes associated with the AEM under different climate conditions, while the variability of the AEM is expected to decrease in the future. Here, we use historical and SSP5-8.5 simulations from 24 models that contributed to CMIP6 to investigate the near-term, mid-term and long-term future links between the AEM and the extreme rainfall events over the Guinea Coast. The extreme rainfall responses to the AEM are reasonably well represented over the 1995–2014 period, although there are substantial biases in their magnitudes. Future changes indicate an increase in the mean and variability of the majority of the extreme indices over the Guinea Coast. The average across the 12 indices of their percentage of long-term changes in mean and variability equals to +10.46 % and +16.44 %, respectively. By contrast, the decreased variability of the AEM in a warmer climate leads to a reduced magnitude of the rainfall extreme responses associated to AEM over the Guinea Coast. The multi-model median values of the long-term changes in the variance explained by the AEM for the different extreme indices range between −8.25 % and −64.97 %. As a consequence, while in absolute there is a projected increase in the variability of most of the extreme rainfall indices, the contribution of the AEM to this variability weakens in a warmer future climate.

Koffi Worou 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 wcd-2022-53', Anonymous Referee #1, 28 Oct 2022
    • AC2: 'Reply on RC1', Koffi Worou, 31 Jan 2023
  • RC2: 'Comment on wcd-2022-53', Anonymous Referee #2, 01 Nov 2022
    • AC3: 'Reply on RC2', Koffi Worou, 31 Jan 2023
  • CC1: 'Comment on wcd-2022-53', Paul-Arthur Monerie, 04 Nov 2022
    • AC4: 'Reply on CC1', Koffi Worou, 31 Jan 2023
  • EC1: 'Comment on wcd-2022-53', Peter Knippertz, 09 Nov 2022
    • AC1: 'Reply on EC1', Koffi Worou, 19 Nov 2022
      • EC2: 'Reply on AC1', Peter Knippertz, 19 Nov 2022

Koffi Worou et al.

Koffi Worou et al.


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Short summary
The Atlantic equatorial mode (AEM) of variability is responsible for 31 % of the year-to-year rainfall variability over the Guinea Coast. We use the current climate models to explore the present-day and future links between the AEM and the extreme rainfall indices over the Guinea Coast. Under future global warming, the total variability of the extreme rainfall indices increases over the Guinea Coast. However, the future impact of the AEM on the extreme events over the Guinea Coast is reduced.