Abstract
Rainfall variability is a crucial factor in food production,water resource planning and ecosystems, especially in regions with scarce freshwaterresources. In West Africa rainfall has been subject to largedecadal and interdecadal variations during the 20th century. The most prominent feature is thereduction in rainfall amount throughout the second half of the century with somerecovery at the end. Among the conceivable mechanisms, which might inducesuch low-frequency variability in West African precipitation, this study isfocussed onsea surface temperature (SST) variations and increasing greenhouse gas (GHG)concentrations. A tool is presented to distinguish between both impacts bymeans of various climate model simulations, which are found to reproduce theobserved rainfall characteristics over West Africa reasonably well.Further, a multi-model approach is usedto evaluate the expected future greenhouse signal in West African rainfall with respect to natural variability and intermodel variations.It is found that observed SST fluctuations, forcing two different atmospheric climate models, are able to reproduce the main features ofobserved decadal rainfall anomalies in the southern part of West Africathroughout the second half of the 20th century. The seasonal response to varying SST isstrongest in summer when the region is undergoing intensive monsoondynamics. Whereas both atmospheric models simulate the observeddrought tendency,following the 1960s, there is some indication that the additional GHG forcing in one model inducessome significantly different rainfall anomalies in recent years, re-initiatingeven positive anomalies relative to the climatological mean which has alsobeen observed since the 1990s. However, thisresult is still subject to model uncertainty.Coupled climate model integrations with different climate change scenariosalsopredict that precipitation, particularly over the Guinea Coast and Sahelregion, will steadily increase into the 21st century. The model-comprehensive signal isstatistically significant with respect to natural variability and modeluncertainty, suggesting that the observed recovery of yearly rainfall overparts of West Africa might actually reflect the beginning impact of risinganthropogenic GHG. The physical mechanism, linking the radiative forcing tothe monsoonal rainfall, probably works via warming of the tropicalAtlantic Ocean.
Similar content being viewed by others
References
Benson, C. and Clay, E. J.: 1998, The Impact of Drought on Sub-Saharan Economies, World Bank Tech. Paper, No. 401, Wold Bank, Washingtion D.C.
Bounoua, L., Collatz, G. J., Los, S. O., Sellers, P. J., Dazlich, D. A., Tucker, C. J., and Randall, D. A.: 2000, ‘Sensitivity of Climate to Changes in NDVI’, J. Climate 13, 2277–2292.
Camberlin, P., Janicot, S., and Poccard, I.: 2001, ‘Seasonality and Atmospheric Dynamics of the Teleconnection between African Rainfall and Tropical Sea-surface Temperature: Atlantic vs. ENSO’, Int. J. Clim. 21, 973–1004.
Chang, P., Saravanan, R., Ji, L., and Hegerl, G. C.: 2000, ‘The Effect of Local Sea Surface Temperature on Atmopsheric Circulation over the Tropical Atlantic Sector’, J. Climate 13, 2195–2216.
Clark, D. B., Xue, Y., Harding, R. J., and Valdes, P. J.: 2001, ‘Modeling the Impact of Land Surface Degradation on the Climate of Tropical North Africa’, J. Climate 14, 1809–1822.
Cook, K. H.: 1999, ‘Generation of the African Easterly Jet and its Role in Determining West African Precipitation’, J. Climate 12, 1165–1184.
Cullen, H. M. and de Menocal, P. B.: 2000, ‘North Atlantic Influence on Tigris-Euphrates Streamflow’,Int. J. Clim. 20, 853–863.
Desanker, P. V. and Justice, C. O.: 2001, ‘Africa and Global Climate Change: Critical Issues and Suggestions for Further Research and Integrated Assessment Modeling’, Clim. Res. 17, 93–103.
Douville, H., Chauvin, F., and Broqua, H.: 2001, ‘Influence of Soil Moisture on the Asian and African Monsoons. Part I: Mean Monsoon and Daily Precipitation’, J. Climate 14, 2381–2402.
Douville, H., Planton, S., Royer, J.-F., Stephenson, D. B., Tyteca, S., Kergoat, L., Lafont, S., and Betts, S. A.: 2000, ‘Importance of Vegetation Feedbacks in Doubled-CO2 Climate Experiments’, J. Geophys. Res. 105(D11), 14841–14861.
Druyan, L. M., Lonergan, P., and Cohen, J.: 1997, ‘Cast Studies of African Wave Disturbances in Gridded Analyses’,Mon. Wea. Rev. 125, 2520–2530.
Feddema, J. J. and Freire, S.: 2001, ‘Soil Degradation, Global Warming and Climate Impacts’, Clim. Res. 17, 209–216.
Gasse, F.: 2001, ‘Hydrological Changes in Africa’, Science 292, 2259–2260.
Giorgi, F. and Francisco, R.: 2000, ‘Uncertainties in Regional Climate Change Prediction: A Regional Analysis of Ensemble Simulations with the HADCM2 Coupled AOGCM’, Clim. Dyn. 16, 169–182.
Gong, C. and Eltahir, E.: 1996, ‘Sources of Moisture for Rainfall inWest Africa’, Water Resour. Res. 32, 3115–3121.
Grist, J. P. and Nicholson, S. E.: 2001, ‘A Study of the Dynamic Factors Influencing the Rainfall Variability in the West African Sahel’, J. Climate 14, 1337–1359.
Hastenrath, S.: 2000, ‘Interannual and Longer Term Variability of Upper-air Circulation over the Tropical Atlantic and West Africa in Boreal Summer’, Int. J. Clim. 20, 1415–1430.
Houghton, J. T., Callandar, B. A., and Varney, S. K. (eds.): 1992, Climate Change 1992, the Supplementary Report to the IPCC Scientific Assessment, Cambridge.
Houghton, J. T., Ding, Y., Griggs, D. J., Noguer, M., Van der Linden, P. J., Dai, X., Maskell, K., and Johnson, C. A. (eds.): 2001, Climate Change 2001, The Scientific Basis, Cambridge.
Houghton, J. T., Jenkins, G. J., and Ephraums, J. J. (eds.): 1990, Climate Change, The IPCC Scientific Assessment, Cambridge.
Hulme, M., Doherty, R., Ngara, T., New, M., and Lister, D.: 2001, ‘African Climate Change: 1900–2100’, Clim. Res. 17, 145–168.
Jenik, J.: 1984, ‘Coastal Upwelling and Distributional Pattern of West African Vegetation’, Preslia 56, 193–204.
Johns, T. C., Carnell, R. E., Crossley, J. F., Gregory, J. M., Mitchell, J. F. B., Senior, C. A., Tett, S. F. B., and Wood, R. A.: 1997, ‘The Second Hadley Centre Coupled Ocean-atmosphere GCM: Model Description, Spinup, and Validation’, Clim. Dyn. 13, 103–134.
Latif, M. and Grötzner, A.: ‘The Equatorial Atlantic Oscillation and its Response to ENSO’, Clim. Dyn. 16, 213–218.
Long, M., Entekhabi, D., and Nicholson, S. E.: 2000, ‘Interannual Variability in Rainfall, Water Vapor Flux, and Vertical Motion over West Africa’, J. Climate 13, 3827–3841.
New, M., Hulme, M., and Jones, P.: 2000, ‘Representing Twentieth-century Space-time Climate Variability. Part II: Development of 1901–96 Monthly Grids of Terrestrial Surface Climate’, J. Climate 13, 2217–2238.
Nicholson, S. E.: 2001, ‘Climatic and Enviromental Change in Africa during the Last Two Centuries’, Clim. Res. 17, 123–144.
Nicholson, S. E. and Palao, I. M.: 1993, ‘A Re-evaluation of Rainfall Variability in the Sahel. Part I. Characteristics of Rainfall Fluctuations’, Int. J. Clim. 13, 371–389.
Nicholson, S. E. and Selato, J. C.: 2000, ‘The Influence of La Niña on African Rainfall’, Int. J. Clim. 20, 1761–1776.
Nicholson, S. E., Some, B., and Kone, B.: 2000, ‘An Analysis of Recent Rainfall Conditions in West Africa, Including the Rainy Season of the 1997 El Niño and the 1998 La Niña Years’, J. Climate 13, 2628–2640.
Paeth, H., Friederichs, P., and Hense, A.: 2001, ‘Covariability and Interaction of North Atlantic Sea Surface Temperature and North Atlantic Oscillation in ECHAM3 Greenhouse-gas Scenario Simulations’, Met. Zeit. 10, 295–307.
Paeth, H. and Hense, A.: 2002, ‘Sensitivity of Climate Change Signals Deduced from Multi-model Monte Carlo Experiments’, Clim. Res. 22, 189–204.
Paeth, H., Hense, A., Glowienka-Hense, R., Voss, R., and Cubasch, U.: 1999, ‘The North Atlantic Oscillation as an Indicator for Greenhouse-gas Induced Climate Change’, Clim. Dyn. 15, 953–960.
Parker, D. E. and Jackson, M.: 1995, The Standard GISST Data Sets: Versions 1 and 2, Workshop on Simulations of the Climate of the 20th Century Using GISST, Bracknell, United Kingdom, Hadley Centre, pp. 50–51.
Poccard, I., Janicot, S., and Camberlin, P.: 2000, ‘Comparison of Rainfall Structures between NCEP/NCAR Reanalyses and Observed Data over Tropical Africa’, Clim. Dyn. 16, 897–915.
Rodwell, M. J., Rowell, D. P., and Folland, C. K.: 1999, ‘Oceanic Forcing of the Wintertime North Atlantic Oscillation and European Climate’, Nature 398, 320–323.
Roeckner, E., Arpe, K., Bengtsson, L., B rinkop, S., Dümenil, L., Esch, M., Kirk, E., Lunkeit, F., Ponater, M., Rockel, B., Sausen, R., Schlese, U., Schubert, S., and Windelband, M.: 1992
Roeckner, E., Arpe, K., Bengtsson, L., Christoph, M., Claussen, M., Dümenil, L., Esch, M., Giorgetta, M., Schlese, U., and Schulzweida, U.: 1996, The Atmospheric General Circulation Model ECHAM-4: Model Description and Simulation of Present-day Climate, Max-Planck-Inst. f. Meteor., Report No. 218, Hamburg.
Ruiz-Barradas, A., Carton, J. A., and Nigam, S.: 2000, ‘Structure of Interannual-to-decadal Climate Variability in the Tropical Atlantic Sector’, J. Climate 13, 3285–3297.
Saha, K. and Saha, S.: 2001, ‘African Monsoons. Part I: Climatological Structure and Circulation’, Mausam 52, 479–510.
Semazzi, F. H. M. and Song, Y.: 2001, ‘A GCM Study of Climate Change Induced by Deforestation in Africa’, Clim. Res. 17, 169–182.
Vizy, E. K. and Cook, K. H.: 2001, ‘Mechanisms by which Gulf of Guinea and Eastern North Atlantic Sea Surface Temperature Anomalies Can Influence African Rainfall’, J. Climate 14, 795–821.
von Storch, H. and Zwiers, F. W.: 1999, Statistical Analysis in Climate Research, Cambridge.
Voss, R., Sausen, R., and Cubasch, U.: 1998, ‘Periodically Synchronously Coupled Integrations with the Atmosphere-ocean General Circulation Model ECHAM3/LSG’, Clim. Dyn. 14, 249–266.
Webster, P. J., Magaña, V. O., Palmer, T. N., Shukla, J., Tomas, R. A., Yanai, M., and Yasunari, T.: 1998, ‘Monsoons: Processes, Predictability, and the Prospects for Prediction’, J. Geophys. Res. 103(C7), 14451–14510.
Zeng, N., Neelin, J. D., Lau, K.-M., and Tucker, C. J.: 1999, ‘Enhancement of Interdecadal Climate Variability in the Sahel by Vegetation Interaction’, Science 286, 1537–1540.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Paeth, H., Hense, A. SST versus Climate Change Signals in West African Rainfall: 20th-Century Variations and Future Projections. Climatic Change 65, 179–208 (2004). https://doi.org/10.1023/B:CLIM.0000037508.88115.8a
Issue Date:
DOI: https://doi.org/10.1023/B:CLIM.0000037508.88115.8a