How will Somali coastal upwelling evolve under future warming scenarios?

M Decastro,F Santos,J M Dias,M Gómez-Gesteira,M C Sousa

doi:10.1038/srep30137

M Decastro, F Santos + Show 3 more

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https://doi.org/10.1038/srep30137

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Journal: Scientific Reports	Publication Date: Jul 21, 2016
Citations: 34	License type: CC BY 4.0

Affiliation: Universidade de Vigo, University of Aveiro

Abstract

Somali upwelling system, the fifth in the world, presents some unique features compared with the other major upwelling systems: 1) it is a Western Boundary Upwelling System located near the Equator and 2) upwelling affects the moisture responsible for monsoon rainfall. The intensity of Somali coastal upwelling during summer was projected for the twenty first century by means of an ensemble of Global Climate Models and Regional Climate Models within the framework of CMIP5 and CORDEX projects, respectively. Regardless global or regional circulation models and the chosen greenhouse warming scenario, the strengthening of Somali coastal upwelling, which increases with latitude, is even higher than observed for the Eastern Boundary Upwelling System. In addition, coastal upwelling strengthening is mainly due to Ekman transport since Ekman pumping shows no clear trend for most of the latitudes. Projected land-sea air temperature and pressure show a clear intensification of land-sea thermal and pressure gradient as a consequence of the global warming, which is likely to affect the strengthening of Somali upwelling verifying the hypothesis of Bakun. As a consequence, projected sea surface temperature warming is less intense nearshore than at oceanic locations, especially at latitudes where upwelling strengthening is more intense.

Highlights

Somali upwelling system, the fifth in the world, presents some unique features compared with the other major upwelling systems: 1) it is a Western Boundary Upwelling System located near the Equator and 2) upwelling affects the moisture responsible for monsoon rainfall
Regardless global or regional circulation models and the chosen greenhouse warming scenario, the strengthening of Somali coastal upwelling, which increases with latitude, is even higher than observed for the Eastern Boundary Upwelling System
The strengthening in Somali coastal upwelling, which increases with latitude, is even higher than observed for Humbolt, Benguela and Canary coastal upwelling systems[23], where strengthening ranges from 0 to 0.01 m2 s−1 dec−1

Summary

Introduction

The fifth in the world, presents some unique features compared with the other major upwelling systems: 1) it is a Western Boundary Upwelling System located near the Equator and 2) upwelling affects the moisture responsible for monsoon rainfall. Since the hypothesis of Bakun, different studies[4,5,6,7,8,9] dealing with coastal upwelling intensification show contradictory results highly dependent on the area, the season and the database In this sense, wind intensification has been analyzed within the framework of global warming for the four major EBUS4: Benguela, California, Humboldt and Canary. The question to be answered now is how these coastal upwelling systems will evolve under different greenhouse warming scenarios along the twenty first century This question was partially addressed by means of an ensemble of climate models developed for the Coupled Model Intercomparison Project phase 5 (CMIP5) along the four major EBUSs23. Causes and implications of coastal upwelling evolution along the twenty first century were evaluated assessing the projections of land-sea thermal difference, cross-shore pressure gradient and sea surface temperature from 2006 to 2099

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