Mecanismos de realimentación positivos y negativos en el impacto de la vegetación en la sequía del Sahel

Fred Kucharski,Ning Zeng

doi:10.5209/rev_fite.2013.v25.43437

Abstract

In this contribution, the vegetation feedback mechanisms on the Sahel drought are revisited and further analysed using the intermediate complexity Atmospheric General Circulation model SPEEDY coupled to the VEGAS dynamic vegetation model. It is found that the albedo feedback provides a strongly positive feedback to the atmosphere-vegetation system. The albedo increase leads to a reduction in net surface radiation that is mainly compensated by reduced evaporation (latent heat loss), providing one major source of the total rainfall response. Another positive feedback is provided by the pressure response to the reduced atmospheric heating in the Sahel region that leads to a high pressure in the Saharan region, thus weakening the Saharan heat low and being favourable for diverging north-easterly wind anomalies in the Sahel region. The major negative feedback is provided by the vegetation impact on evaporation, which limits the response in soil wetness and is thus stabilizing the coupled atmosphere-vegetation system.

Highlights

The physical mechanism for the Sahel drought that peaked in the 1980s has been intensively investigated in the scientific literature over the last decades
The Sahel drought may be considered as part of a global tendency for monsoons to weaken in the second half of the 20th century, and the driving sea surface temperature (SST) pattern has contributions from the Atlantic Multidecadal Oscillation (AMO), Interdecadal Pacific Oscillation (IPO) and from global warming (Zhou et al 2008a, b; Mohino et al, 2011)
In the experiment ALB_VEG we prescribe vegetation cover to reduce and the albedo to increase by 5% in the Sahel region (19W to 35 E, 6 to 17N) with respect to CNTRL, otherwise the simulation is identical to CNTRL

Summary

Introduction

The physical mechanism for the Sahel drought that peaked in the 1980s has been intensively investigated in the scientific literature over the last decades. Kucharski et al (2013a), in the following referred to as K13, analysed the vegetation feedback on the Sahel drought in more details using large ensembles of simulations with the intermediate complexity Atmospheric General Circulation Model (AGCM) SPEEDY (or ICTPAGCM) coupled to the dynamic vegetation model VEGAS (UMD-ICTP).

Results

Conclusion