Bias reduction in decadal predictions of West African monsoon rainfall using regional climate models

• Published in: Journal of geophysical research. Atmospheres Vol. 121; no. 4; pp. 1715 - 1735
• Main Authors: Paxian, A., Sein, D., Panitz, H.‐J., Warscher, M., Breil, M., Engel, T., Tödter, J., Krause, A., Cabos Narvaez, W. D., Fink, A. H., Ahrens, B., Kunstmann, H., Jacob, D., Paeth, H.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 27-02-2016
• Subjects: Aerosols; African easterly waves; African monsoon; Atmosphere; Atmospheric models; Atmospheric precipitations; Bias; bias correction; Boundary conditions; Brackish; Climate; Climate models; Climatology; Coastal environments; Computer simulation; Convergence; Convergence zones; decadal climate prediction; Easterly waves; Evaporation; Farming; Food; Food production; Foods; Forecasting; Geophysics; Global climate; Global climate models; High resolution; Hypotheses; Interactions; Intertropical convergence zone; Land cover; Marine; Mathematical models; Monsoon rainfall; Monsoons; Ocean circulation; ocean coupling; Ocean models; Ocean-atmosphere interaction; Policies; Precipitation; Rain; Rainfall; RCM; Reduction; Regional; regional climate modeling; Regional climate models; Regional climates; Resolution; Sea surface; Sea surface temperature; Soil; Soils; Surface temperature; Traditional foods; Vegetation; Weather; Weather forecasting; West African monsoon rainfall; Westerlies; Sahel (African region); ASE, Africa; AS, Atlantic, Intertropical Convergence Zone; Guinea; AS, Tropical Atlantic; Africa
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2015JD024143

The West African monsoon rainfall is essential for regional food production, and decadal predictions are necessary for policy makers and farmers. However, predictions with global climate models reveal precipitation biases. This study addresses the hypotheses that global prediction biases can be reduced by dynamical downscaling with a multimodel ensemble of three regional climate models (RCMs), a RCM coupled to a global ocean model and a RCM applying more realistic soil initialization and boundary conditions, i.e., aerosols, sea surface temperatures (SSTs), vegetation, and land cover. Numerous RCM predictions have been performed with REMO, COSMO‐CLM (CCLM), and Weather Research and Forecasting (WRF) in various versions and for different decades. Global predictions reveal typical positive and negative biases over the Guinea Coast and the Sahel, respectively, related to a southward shifted Intertropical Convergence Zone (ITCZ) and a positive tropical Atlantic SST bias. These rainfall biases are reduced by some regional predictions in the Sahel but aggravated by all RCMs over the Guinea Coast, resulting from the inherited SST bias, increased westerlies and evaporation over the tropical Atlantic and shifted African easterly waves. The coupled regional predictions simulate high‐resolution atmosphere‐ocean interactions strongly improving the SST bias, the ITCZ shift and the Guinea Coast and Central Sahel precipitation biases. Some added values in rainfall bias are found for more realistic SST and land cover boundary conditions over the Guinea Coast and improved vegetation in the Central Sahel. Thus, the ability of RCMs and improved boundary conditions to reduce rainfall biases for climate impact research depends on the considered West African region.
Key Points
RCMs reduce Sahel rainfall bias of GCM predictions but raise Guinea Coast bias
Coupled atmosphere‐ocean RCMs improve both Atlantic SST and WAM rainfall biases
Improved SST, vegetation, and land cover boundary conditions reduce some biases