GEP  Vol.8 No.3 , March 2020
Interannual Variability of Rainfall over the West Africa Sahel
Abstract: Interannual variability of the precipitation over West Africa Sahel is analyzed based on 32 years (1979-2010) from monthly and daily database of the Global Precipitation Climatology Project (GPCP). In this region, we found that there is a link between the West Africa Monsoon (WAM) and the daily means of the precipitation in the summer, unseasonal rains can occur in the transition seasons and even in the heart of the dry season. Rainfall is the most important element for agro-pastoral activities in this region. The 850-hPa wind and wind divergence structure show a maximum convection over Mountain region (Fouta-Djalon and Mont-Cameroon) which corresponds to the high precipitation and OLR observed in these regions. The trend and empirical orthogonal function (EOF) of the precipitation are presented, including the mid-July variability of the precipitation. The dominant EOF of GPCP precipitation accounts for around 25.3% of the variance with slightly large amplitude in the north while relatively small in the equatorial band respectively. The second and third EOF which accounts for 20.5% and 14%, describes a longitudinal contrast with a zonal gradient.
Cite this paper: Dia-Diop, A. , Zebaze, S. , Wade, M. , Djiondo, R. , Diop, B. , Efon, E. and Lenouo, A. (2020) Interannual Variability of Rainfall over the West Africa Sahel. Journal of Geoscience and Environment Protection, 8, 85-101. doi: 10.4236/gep.2020.83007.

[1]   Boone, A., De Rosnay, P., Balsamo, G. et al. (2009). The AMMA Land Surface Model Intercomparison Project (ALMIP). Bulletin of the American Meteorological Society, 90, 1865-1880.

[2]   Daniell, P. J. (1946). Discussion on the Symposium on Autocorrelation in Time Series. Journal of the Royal Statistical Society, 8, 88-90.

[3]   Dee, D. P. et al. (2011). The ERA-Interim Reanalysis: Configuration and Performance of the Data Assimilation System. Quarterly Journal of the Royal Meteorological Society, 137, 553-597.

[4]   Diallo, I., Sylla, M. B., Giorgi, F., Gaye, A. T., & Camara, M. (2012). Multimodel GCM-RCM Ensemble Based Projections of Temperature and Precipitation over West Africa for the Early 21st Century. International Journal of Geophysics, 2012, Article ID: 972896.

[5]   Dinku, T., Ceccato, P., Grover-Kopec, E., Lemma, M., Connor, S. J., & Ropelewski, C. F. (2007). Validation of Satellite Rainfall Products over East Africa’s Complex Topography. International Journal of Remote Sensing, 28, 1503-1526.

[6]   Fontaine, B., & Janicot, S. (1992). Wind-Field Coherence and Its Variations over West Africa. Journal of Climate, 5, 521-523.<0512:WFCAIV>2.0.CO;2

[7]   Fontaine, B., Janicot, S., & Moron, V. (1995). Rainfall Anomaly Patterns and Wind Field Signals over West Africa in August (1958-1989). Journal of Climate, 8, 1503-1510.<1503:RAPAWF>2.0.CO;2

[8]   Giannini, A., Saravanan, R., & Chang, P. (2003). Oceanic Forcing of Sahel Rainfall on Interannual to Interdecadal Time Scales. Science, 302, 1027-1030.

[9]   Gilman, D., Fuglister, P., & Miitchell, J. M. (1963). On the Power Spectrum of Red Noise. Journal of the Atmospheric Sciences, 20, 1982-1984.<0182:OTPSON>2.0.CO;2

[10]   Hagos, S. M., & Cook, K. H. (2007). Dynamics of the West African Monsoon Jump. Journal of Climate, 20, 5264-5284.

[11]   Hoerling. M., Hurrell, J., Eischeid, J., & Phillips, A. (2006). Detection and Attribution of Twentieth-Century Northern and Southern African Rainfall Change. Journal of Climate, 19, 3989-4008.

[12]   Janicot, S. (2011). Intra-Seasonal Variability of the West African Monsoon. Atmospheric Science Letters, 12, 24-30.

[13]   Janicot, S., Mounier, F., & Diedhiou, A. (2008). Les ondes atmosphériques d’échelle synoptique dans la mousson d’Afrique de l’Ouest et centrale: Ondes d’est et onde de Kelvin. Sécheresse, 19, 13-22.

[14]   Jenkins, G., Kucera, P., Joseph, E., Fuentes, J., Gaye, A., Gerlach, J., Roux, F., Viltard, N., Papazzoni, M., Protat, A., Bouniol, D., Reynolds, A., Arnault, J., Badiane, D., Kebe, F., Camara, M., Sall, S., Ndiaye, S. A., & Deme, A. (2010). Observations of Weather Features in Senegal during the AMMA SOP-3 Period. Journal of Geophysical Research: Atmospheres, 115, D18108.

[15]   Kidson, J. W. (1977). African Rainfall and Its Relation to Upper Air Circulation. Quarterly Journal of the Royal Meteorological Society, 103, 441-456.

[16]   Kiladis, G. N., Wheeler, M. C., Haertel, P. T., Straub, K. H., & Roundy, P. E. (2009). Convectively Coupled Equatorial Waves. Reviews of Geophysics, 47, RG2003.

[17]   Lamb, P. J. (1978). Case Studies of Tropical Atlantic Surface Circulation Patterns during Recent Sub-Saharan Weather Anomalies: 1967 and 1968. Monthly Weather Review, 106, 482-491.<0482:CSOTAS>2.0.CO;2

[18]   Le Barbé, L., Lebel, T., & Tapsoba, D. (2002). Rainfall Variability in West Africa during the Years 1950-90. Journal of Climate, 15, 187-202.<0187:RVIWAD>2.0.CO;2

[19]   Lebel, T., Cappelaere, B., Galle, S. et al. (2009). AMMA-CATCH Studies in the Sahelian Region of West-Africa: An Overview. Journal of Hydrology, 375, 3-13.

[20]   Lenouo, A., Mkankam, K. F., & Yepdjuo, E. (2005). Weak Interaction in the African Easterly Jet. Annales Geophysicae, 23, 1637-1643.

[21]   Lenouo, A., Sall, M. S., Badiane, D., Gaye, A. T., & Mkankam, K. F. (2016). Intense Convection over West Africa during AMMA SOP3 Experiment. Atmospheric Research, 180, 1-11.

[22]   Liebmann, B., & Smith, C. A. (1996). Description of a Complete (Interpolated). Outgoing Longwave Radiation Dataset. Bulletin of the American Meteorological Society, 77, 1275-1277.

[23]   McCollum, J., Nelkin, E., Klotter, D., Berte, Y., Diallo, B. M., Gaye, I., Kpabeba, G., Ndiaye, O., Noukpozounkou, T. M. M., Thiam, A., Toure, A. A., Traore, K., Nicholson, S. E., & Some, B. (2003). Validation of TRMM and Other Rainfall Estimates with a High-Density Gauge Dataset for West Africa. Part I: Validation of GPCC Rainfall Product and Pre-TRMM Satellite and Blended Products. Journal of Applied Meteorology, 40, 1355-1368.<1355:VOTAOR>2.0.CO;2

[24]   Ndao, S., Rinelle, D. N., Badiane, D., Lenouo, A., & Sall, S. M. (2019). Study of Boundary Layer Height over West Africa. Journal of Geoscience and Environment Protection, 7, 179-194.

[25]   Newell, R. E., & Kidson, J. W. (1984). African Mean Wind Changes in Sahelian Wet and Dry Periods. Journal of Climatology, 4, 1-7.

[26]   Nguyen, T. T. H., & Duvel, J. P. (2008). Synoptic Wave Perturbations and Convective Systems over Equatorial Africa. Journal of Climate, 21, 6372-6388.

[27]   Nicholson, S. E. (1981). Rainfall and Atmospheric Circulation during Drought Periods and Wetter Years in West Africa. Monthly Weather Review, 109, 2191-2208.<2191:RAACDD>2.0.CO;2

[28]   Nicholson, S. E. (2008). The Intensity, Location and Structure of the Tropical Rainbelt over West Africa as Factors in Interannual Variability. International Journal of Climatology, 28, 1775-1785.

[29]   Nicholson, S. E. (2013). The West African Sahel: A Review of Recent Studies on the Rainfall Regime and Its Interannual Variability. Meteorology, 2013, Article ID: 453521.

[30]   Nicholson, S. E., & Grist, J. P. (2001). A Conceptual Model for Understanding Rainfall Variability in the West African Sahel on Interannual and Interdecadal Timescales. International Journal of Climatology, 21, 1733-1757.

[31]   Nicholson, S. E., & Webster, P. J. (2007). A Physical Basis for the Interannual Variability of Rainfall in the Sahel. Quarterly Journal of the Royal Meteorological Society, 133, 2065-2084.

[32]   Paeth, H., & Hense, A. (2004). SST versus Climate Change Signals in West African Rainfall: 20th-Century Variations and Future Projections. Climatic Change, 65, 179-208.

[33]   Redelsperger, J. L., Thorncroft, C. D., Diedhiou, A., Lebel, T., Parker, D. J., & Polcher, J. (2006). African Monsoon Multidisciplinary Analysis: An International Research Project and Field Campaign. Bulletin of the American Meteorological Society, 87, 1739-1746.

[34]   Reed, R. J., Norquist, D. C., & Recker, E. E. (1977). The Structure and Properties of African Wave Disturbances as Observed during Phase III of GATE. Monthly Weather Review, 105, 317-333.<0317:TSAPOA>2.0.CO;2

[35]   Roundy, P. E. (2008). Analysis of Convectively Coupled Kelvin Waves in the Indian Ocean MJO. Journal of the Atmospheric Sciences, 65, 1342-1359.

[36]   Ruiz, F. et al. (2010). Validation of Satellite Rainfall Products over Colombia. Journal of Applied Meteorology and Climatology, 49, 1004-1014.

[37]   Salack, S., Klein, C., Giannini, A., Sarr, B., Worou, O. N., Belko, N., Bliefernicht, J., & Kunstmann, H. (2016). Global Warming Induced Hybrid Rainy Seasons in the Sahel. Environmental Research Letters, 11, 10.

[38]   Semazzi, H. F. M., & Sun, L. (1997). The Role of Orography in Determining the Sahelian Climate. International Journal of Climatology, 17, 581-596.<581::AID-JOC134>3.0.CO;2-E

[39]   Tchakoutio, S. A., Nzeukou, A. T., & Tchawoua, C. (2012). Intraseasonal Atmospheric Variability and Its Interannual Modulation in Central Africa. Meteorology and Atmospheric Physics, 117, 167-179.

[40]   Thomas, M., John, C. H. C., Alexander, G., & Nicolas, J. C. (2009). Temporal Precipitation Variability versus Altitude on a Tropical High Mountain: Observations and Mesoscale Atmospheric Modeling. Quarterly Journal of the Royal Meteorological Society, 135, 1439-1455.

[41]   Thorncroft, C. D., Parker, D. J., & Burton, R. R. (2003). The JET2000 Project—Aircraft Observations of the African Easterly Jet and African Easterly Waves. Bulletin of the American Meteorological Society, 84, 337-351.

[42]   Torrence, C., & Compo, G. P. (1998). A Practical Guide to Wavelet Analysis. Bulletin of the American Meteorological Society, 79, 61-78.<0061:APGTWA>2.0.CO;2

[43]   Vondou, D. A., Nzeukou, A., Lenouo, A., & Mkankam, K. F. (2010). Seasonal Variations in the Diurnal Patterns of Convection in Cameroon-Nigeria and Their Neighbouring Areas. Atmospheric Science Letters, 11, 290-300.

[44]   Wang, G., & Eltahir, E. A. B. (2000). The Role of Vegetation Dynamics in Enhancing the Low-Frequency Variability of the Sahel Rainfall. Water Resources Research, 36, 1013-1021.

[45]   Wheeler, M. C., & Kiladis, G. N. (1999). Convectively Coupled Equatorial Waves: Analysis of Clouds and Temperature in the Wave-Number Frequency Domain. Journal of the Atmospheric Sciences, 56, 374-399.<0374:CCEWAO>2.0.CO;2

[46]   Wilks, D. (2011). Statistical Methods in the Atmospheric Sciences (3rd ed., Vol. 100, pp. 704). New York: International Geophysics.

[47]   Zebaze, S., Lenouo, A., Tchawoua, C., & Janicot. C. (2015). Synoptic Kelvin Type Perturbation Waves over Congo Basin over the Period 1979-2010. Journal of Atmospheric and Solar-Terrestrial Physics, 130-131, 43-56.

[48]   Zebaze, S., Lenouo, A., Tchawoua, C., & Mkankam, K. F. (2017). Interaction between Moisture Transport and Kelvin Waves Events over Equatorial Africa through ERA-Interim. Atmospheric Science Letters, 18, 300-306.