Climate Dynamics

, Volume 36, Issue 5–6, pp 925–944 | Cite as

WRF/ARPEGE-CLIMAT simulated climate trends over West Africa

  • N. Vigaud
  • P. Roucou
  • B. Fontaine
  • S. Sijikumar
  • S. Tyteca
Article
First Online:
Received:
Accepted:

Abstract

The Weather Regional Forecast (WRF) model is used in this study to downscale low-resolution data over West Africa. First, the performance of the regional model is estimated through contemporary period experiments (1981–1990) forced by ARPEGE-CLIMAT GCM output (ARPEGE) and ERA-40 re-analyses. Key features of the West African monsoon circulation are reasonably well represented. WRF atmospheric dynamics and summer rainfall compare better to observations than ARPEGE forcing data. WRF simulated moisture transport over West Africa is also consistent in both structure and variability with re-analyses, emphasizing the substantial role played by the West African Monsoon (WAM) and African Easterly Jet (AEJ) flows. The statistical significance of potential climate changes for the A2 scenario between 2032 and 2041 is enhanced in the downscaling from ARPEGE by the regional experiments, with substantial rainfall increases over the Guinea Gulf and eastern Sahel. Future scenario WRF simulations are characterized by higher temperatures over the eastern Tropical Atlantic suggesting more evaporation available locally. This leads to increased moisture advection towards eastern regions of the Guinea Gulf where rainfall is enhanced through a strengthened WAM flow, supporting surface moisture convergence over West Africa. Warmer conditions over both the Mediterranean region and northeastern Sahel could also participate in enhancing moisture transport within the AEJ. The strengthening of the thermal gradient between the Sahara and Guinean regions, particularly pronounced north of 10°N, would support an intensification of the AEJ northwards, given the dependance of the jet to the position/intensity of the meridional gradient. In turn, mid-tropospheric moisture divergence tends to be favored within the AEJ region supporting southwards deflection of moist air and contributing to deep moist convection over the Sahel where late summer rainfall regimes are sustained in the context of the A2 scenario regional projections. In conclusion, WRF proved to be a valuable and efficient tool to help downscaling GCM projections over West Africa, and thus assessing issues such as water resources vulnerability locally.

Keywords

Moisture Transport West African Monsoon Guinean Coast Contemporary Period West African Region 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Notes

Acknowledgments

The authors are most thankful to the anonymous reviewers for their constructive suggestions and substantial contribution to the paper. N. Vigaud would like to acknowledge the financial support of the RESSAC (Vulnérabilité des Ressources en Eau Superficielle au Sahel aux Evolutions Anthropiques et Climatiques à moyen terme) program from the Agence Nationale pour la Recherche (ANR-06-VULN-017-02). This study was supported by the European Commission 6th Framework Program (ENSEMBLES, contract GOCE-CT-2003-505539). Regional experiments were performed using HPC ressources from GENCI-[CCRT/CINES/IDRIS] (Grant 2009-91320). ECMWF ERA-40 re-analyses used in this study were obtained from the ECMWF data server, IRD in situ daily precipitation data, CMAP and GPCP rainfall from the referring institutions.

References

  1. Adler R, Huffman G, Chang A, Ferraro R, Xie P, Janowiak J, Rudolf B, Schneider U, Curtis S, Bolvin D, Gruber A, Susskind J, Arkin P (2003) The version 2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979-present). J Hydrometeor 4:1147–1167CrossRefGoogle Scholar
  2. Alexander M, Schubert S (1990) Regional earth-atmosphere energy balance estimates based on assimilations with a GCM. J Clim 3:15–31CrossRefGoogle Scholar
  3. Biasutti M, Giannini A (2006) Robust Sahel drying in response to late 20th century forcings. Geophys Res Lett 33. doi:  10.1029/2006GL026067
  4. Cadet D, Nnoli N (1987) Water vapour transport over West Africa and the Atlantic Ocean during summer 1979. Quart J Roy Met Soc 113:581–602CrossRefGoogle Scholar
  5. Caminade C, Terray P (2009) Twentieth century Sahel rainfall variability as simulated by the ARPEGE AGCM, and future changes. Clim Dyn. doi:  10.1007/s00382-009-0545-4
  6. Castro C, Pielke R, Leoncini G (2005) Dynamical downscaling: assessment of value retained and added using Regional Atmospheric Modeling System (RAMS). J Geophys Res 110. doi:  10.1029/2004JDO04721
  7. Cook K (1998), Generation of the African Easterly Jet and its role in determining West African precipitation. J Clim 12:1165–1184CrossRefGoogle Scholar
  8. Déqué M (1999) Documentation ARPEGE-CLIMAT. Tech. report, Centre de National de Recherche Météorologiques. Météo-France, Toulouse, FranceGoogle Scholar
  9. Déqué M, Devreton C, Braun A, Cariolle D (1994) The climate version of the ARPEGE-IFS: a contribution of the French community climate modeling. Clim Dyn 10:249–266CrossRefGoogle Scholar
  10. d’Orgeval T, Polcher J, Li L (2006) Uncertainties in modelling future hydrological change over West Africa. Clim Dyn 26:93–108CrossRefGoogle Scholar
  11. Douville H, Mélia DS, Tyteca S (2006) On the origin of uncertainties in the global land precipitation response to global warming. Clim Dyn 26:367–385CrossRefGoogle Scholar
  12. Fall S, Semazzi F, Dutta SND, Anyah R, Bowden J (2006) The spatiotemporal climate variability over senegal and its relationship to global climate change. Int J Climatol 26:2057–2076CrossRefGoogle Scholar
  13. Fontaine B, Janicot S (1992) Wind-filed coherence and its variations over West Africa. J Clim 5:512–524CrossRefGoogle Scholar
  14. Fontaine B, Janicot S, Moron V (1995) Rainfall anomaly patterns and wind field signals over West Africa in August (1958–1989). J Clim 8:1503–1510CrossRefGoogle Scholar
  15. Fontaine B, Roucou P, Trzaska S (2003) Atmospheric water cycle and moisture fluxes in the West African monsoon: mean annual cycles and relationship using NCEP/NCAR reanalysis. Geophys Res Lett 30:11–17CrossRefGoogle Scholar
  16. Fontaine B, Louvet S, Roucou P (2008) Definition and predictability of an OLR-based West African monsoon onset. Int J Climatol 28:1787–1798CrossRefGoogle Scholar
  17. Gong C, Eltahir E (1996) Sources of moisture for rainfall in West Africa. Wat Resour Res 32:3115–3121CrossRefGoogle Scholar
  18. Hastenrath S, Lamb P (1977) Some aspects of circulation and climate over the eastern equatorial Atlantic. Mon Wea Rev 105:1019–1023CrossRefGoogle Scholar
  19. Janicot S (1992) Spatio-temporal variability of West African rainfall. Part I: Regionalization and typings. J Clim 5:489–497CrossRefGoogle Scholar
  20. Janowiak J (1988) An investigation of interannual rainfall variability in Africa. J Clim 1:240–255CrossRefGoogle Scholar
  21. Joly M, Voldoire A, Douville H, Terray P, Royer J (2007) African monsoon teleconnections with tropical SSTs: validation and evolution from a set of IPCC4 simulations. Clim Dyn 29:1–20CrossRefGoogle Scholar
  22. Kanamaru H, Salvucci G (2003) Adjustments for wind sampling errors in an estimate of the atmospheric water budget of the mississipi river basin. J Hydrometeor 4:518–529CrossRefGoogle Scholar
  23. Lamb PJ (1983) West African water vapor variations between recent contrasting Subsaharan rainy season. Tellus 35:198–212Google Scholar
  24. Lamb PJ (1985) Rainfall in subsaharan West Africa during 1941–83. Z Gletscherk Glazialgeol 21:131–139Google Scholar
  25. Le Barbé L, Lebel T (1989) Analysis of regional precipitation patterns in West Africa based on the low of leaks. In: 4th AMS International meeting on statistical climatologyGoogle Scholar
  26. Le Barbé L, Lebel T, Tapsoba D (2002) Rainfall variability in West Africa during the years 1950–1990. J Clim 15:187–202CrossRefGoogle Scholar
  27. Lo J-F, Yang Z, Pielke R (2008) Assessment of three dynamical climate downscaling methods using the Weather Regional Forecasting (WRF) model. J Geophys Res 113. doi:  10.1029/2007JD009216
  28. Maynard K, Royer J, Chauvin F (2002) Impact of greenhouse warming on the West African summer monsoon. Clim Dyn 19:499–514CrossRefGoogle Scholar
  29. Nakicenovic N, Davidson O, Davis G, Grübler A, Kram T, Rovere ELL, Metz B, Morita T, Pepper W, Pitcher H, Sankovski A, Shukla P, Swart R, Watson R, Dadi Z (eds) (2000) Special report on emissions scenarios: a special report of working group III of the intergovernmental panel on climate change. Cambridge University Press, 599 ppGoogle Scholar
  30. Nicholson SE (1986) The spatial coherence of rainfall anomalies: interhemispheric teleconnections. J Clim Appl Meteor 25:1365–1381CrossRefGoogle Scholar
  31. Peters M, Tetzlaff G (1988) The structure of West African squall lines and their environmental moisture budget. Meteor Atmos Phys 39:74–84CrossRefGoogle Scholar
  32. Philippon N (2007) Previsions des cumuls saisonniers de precipitations Juillet-Aout-Septembre au Sahel pour 2007. In: AMMA W.P.1.1.3. Proceedings, pp 1–7Google Scholar
  33. Ramel R, Gallée H, Messager C (2006) On the northward shift of the West African monsoon. Clim Dyn 26:429–440CrossRefGoogle Scholar
  34. Rockel B, Castro C, Pielke R, von Storch H, Leoncini G (2008) Dynamical downscaling: assessment of model system dependant retained and added variability for two different regional climate models. J Geophys Res. doi:  10.1029/2007JD0099461
  35. Rowell D, Folland C, Maskell K, Owen J, Ward M (1992) Modelling the influence of global sea surface temperatures on the variability and predictability of seasonal Sahelian rainfall. Geophys Res Lett 19:905–908CrossRefGoogle Scholar
  36. Semenov M, Brooks R, Barrow E, Richardson C (1998) Comparison of the WGEN and LARS-WG stochastic weather generators in diverse climates. Clim Res 10:95–107CrossRefGoogle Scholar
  37. Shamarock W, Klemp J, Dudhia J, Gill D, Barker M, Wang W, Powers J (2005) A description of the advanced research WRF version 2. NCAR technical note, NCAR/TN-468+(STR)Google Scholar
  38. Sijikumar S, Roucou P, Fontaine B (2006) Monsoon onset over Sudan-Sahel: simulations by regional scale model MM5. Geophys Res Lett 33. doi:  10.1029/2005GL024819
  39. Sultan B, Janicot S (2000) Abrupt shift of the ITCZ over West Africa and intra-seasonal variability. Geophys Res Lett 27:3353–3356CrossRefGoogle Scholar
  40. Sultan B, Janicot S (2003) The West African Monsoon dynamics. Part II: the preonset and onset of the summer monsoon. J Clim 16:3407–3427CrossRefGoogle Scholar
  41. Trenberth K (1991) Climate diagnostics from global analyses: conservation of mass in ECMWF analyses. J Clim 4:707–722CrossRefGoogle Scholar
  42. Trenberth K (1997) Using atmospheric budgets as a constraint on surface fluxes. J Clim 10:2796–2809CrossRefGoogle Scholar
  43. Vigaud N, Richard Y, Rouault M, Fauchereau N (2007) Water vapour from the tropical atlantic and summer rainfall in tropical southern africa. Clim Dyn. doi:   10.1007/s00382-006-0186-9
  44. Vrac M, Stein M, Hayhoe K (2007) Statistical downscaling of precipitation through nonhomogeneous stochastic weather typing. Clim Res 34:169–184. doi:  10.3354/cr00696 Google Scholar
  45. Wilks D, Wilby R (1999) The weather generation game: a review of stochastic weather model. Prog Phys Geogr 23:329–357Google Scholar
  46. Xie P, Arkin P (1996) Analysis of global monthly precipitation using gauge observations, satellite estimates, and numerical model predictions. J Clim 9:840–858CrossRefGoogle Scholar
  47. Xie P, Arkin P (1997) Global precipitation: a 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull Amer Meteor Soc 78:2539–2558CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • N. Vigaud
    • 1
  • P. Roucou
    • 1
  • B. Fontaine
    • 1
  • S. Sijikumar
    • 2
  • S. Tyteca
    • 3
  1. 1.Centre de Recherches de ClimatologieUMR 5210 CNRS, Université de BourgogneDijonFrance
  2. 2.Space Physics Laboratory, Vikram Sarabhai Space CenterTrivandrumIndia
  3. 3.CNRM/GAME, URA 1357 CNRS/Météo-FranceToulouseFrance

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