This study analyzes the spatio-temporal distribution of daily rainfall data from 13 stations in the country of Senegal located in the North-West of Africa. These data, covering the period 1950-2010, are extracted from the database of the Regional Study Center for the Improvement of Drought Adaptation (CERAAS). They allow to calculate, in each station, dry episodes and their sequences and the results reveal a latitudinal variability of class 1 breaks (1 - 3 days) with the highest values recorded in the south. Unlike the class 2 episodes (greater or equal than 15 days), the latitudinal gradient is less pronounced but they are more frequent in the north. For most of the regions studied, a break in the trend towards an increase in dry sequences can be noted, most often at the beginning of the 1970s, which coincides with the start of the great drought of the 1970s decade. For all sites, the frequency of dry episodes of class 1 (1 - 3 days) exceeds 70%. The frequency of class 2 of dry episodes (greater or equal than 15 days) decreased from 30% in 1951-1970 to 18% in 1991-2010 in the region of Thiès; from 25% in 1951-1970 to 20% in 1991-2010 in Louga; from 22% in 1951-1970 to 18% in 1991-2010 in Tamba; 23% in 1951-1970 to 15% in 1991-2010 in Ziguinchor; 25% in 1951-1970 to 16% in 1991-2010 in Kolda; 22% in 1951-1970 to 18% in 1991-2010 in Diourbel and finally 20% in 1951-1970 to 17% in 1991-2010 in Fatick. Over the whole period of study, the spatial distribution of the number of dry periods in class 1 is higher in the South than in the Center and in the North of Senegal. For class 2 breaks, the latitudinal gradient is less pronounced and the minimum number of dry periods in this class is recorded in the south, especially in Ziguinchor. However, the maximum is observed in the Center. In the Northern region (Saint-Louis), classes 3 and 4 are much more frequent. This spatial variability of rainfall breaks is clearly associated with the rainfall gradient between the North and the South. The temporal evolution of the numbers of each class intrinsically follows the evolution of the ITCZ.
References
[1]
ANSD (2019). https://satisfaction.ansd.sn/
[2]
Barron, J. A., Heusser, L. E., Herbert, T. D., Timothy, D., & Lyle, M. W. (2003). High-Resolution Sedimentological and Paleontological Record of ODP Site 167 1019. PANGAEA. https://doi.org/10.1594/PANGAEA.841955
[3]
Benzerti, Z., & Habaieb, H. (2001). étude de la persistance de la secheresse en Tunisie par utilisation des chaînes de Markov (1909-1996). Secheresse, 12, 215-220.
[4]
Bichet, A., & Diedhiou, A. (2018). Less Frequent and More Intense Rainfall along the Coast of the Gulf of Guinea in West and Central Africa (1981-2014). Climate Research, 76, 191-201. https://doi.org/10.3354/cr01537
[5]
Fodé, M., & Adamou, O. M. (1996). Analyse des séquences sèches au Niger de 1950 à 1991. In G. Bernard (Ed.), Problèmes de validation des méthodes d’estimation des précipitations par satellite en Afrique intertropicale (pp. 189-224). ORSTOM.
[6]
Garcia, C. C., & Martin-Vide, J. (1993). Analyse par la chaîne de Markov de la sécheresse dans le sud-est de l’Espagne. Science et Changements Planétaires/Sécheresse, 4, 123-129.
[7]
IPCC (2016). Climate Change and Land: An IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse Gas Fluxes in Terrestrial Ecosystems [P. R. Shukla, J. Skea, E. Calvo Buendia, V. Masson-Delmotte, H.-O. Pörtner, D. C. Roberts, P. Zhai, R. Slade, S. Connors, R. van Diemen, M. Ferrat, E. Haughey, S. Luz, S. Neogi, M. Pathak, J. Petzold, J. Portugal Pereira, P. Vyas, E. Huntley, K. Kissick, M. Belkacemi, & J. Malley (Eds.)]. In Press.
[8]
IPCC (2019). IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems. https://www.ipcc.ch/report/srccl/
[9]
Lebel, T., Parker, D. J., Flamant, C., Bourlès, B., Marticorena, B., Mougin, E., Peugeot, C., Diedhiou, A., Haywood, J. M., Ngamini, J. B., Polcher, J., Redelsperger, J.-L., & Thorncroft, C. D. (2010). The AMMA Field Campaigns: Multiscale and Multidisciplinary Observations in the West African Region. Quarterly Journal of the Royal Meteorological Society, 136, 8-33. https://doi.org/10.1002/qj.486
[10]
Moron, V., Robertson, A. W., & Ward, M. N. (2006). Seasonal Predictability and Spatial Coherence of Rainfall Characteristics in the Tropical Setting of Senegal. Monthly Weather Review, 134, 3248-3262. https://doi.org/10.1175/MWR3252.1
[11]
Porkka, M. et al. (2021). Is Wetter Better? Exploring Agriculturally-Relevant Rainfall Characteristics over Four Decades in the Sahel. Environmental Research Letters, 16, Article ID: 035002. https://doi.org/10.1088/1748-9326/abdd57
[12]
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. https://doi.org/10.1175/BAMS-87-12-1739
[13]
Sagna, P., Ndiaye, O., Diop, C., Niang, A. D., & Sambou, P. C. (2016). Les variations recentes du climat constatees au Senegal sontelles en phase avec les descriptions donnees par les scenarios du GIEC? Pollution-Atmospherique, Climat, Sante, Societe, 227.
[14]
Salack, S., Muller, B., Gaye, T. A., Hourdin, F., & Cissé, N. (2012). Analyses multi-échelles des pauses pluviométriques au Niger et au Sénégal. Sécheresse, 23, 3-13.
[15]
Sané, T. (2003). La variabilité climatique et ses conséquences sur l’environnement et les activités humaines en Haute-Casamance (Sud Sénégal). Thèse de 3ème cycle, Université Cheikh Anta Diop, 370 p.
[16]
Sané, T., Diop, M., & Sagna, P. (2008). étude de la qualité de la saison pluvieuse en Haute-Casamance (Sud Sénégal). Science et Changements Planétaires/Sécheresse, 19, 23-28.
[17]
Segele, Z., & Lamb, P. (2005). Characterization and Variability of Kiremt Rainy Season over Ethiopia. Meteorology and Atmospheric Physics, 89, 153-180. https://doi.org/10.1007/s00703-005-0127-x
[18]
Sivakumar, M. V. K. (1992). Empirical Analysis of Dry Spells for Agricultural Applications in West Africa. Journal of Climate, 5, 532-539. https://doi.org/10.1175/1520-0442(1992)005<0532:EAODSF>2.0.CO;2
[19]
Sultan, B., Lalou, R., Sanni, M. A. et al. (2011). Les Sociétés Rurales face aux changements climatiques et environmentaux en Afrique de l’Ouest. https://www.locean-ipsl.upmc.fr/~ESCAPE/
[20]
Wilhite, D. A., & Glantz, M. H. (1985). Understanding the Drought Phenomenon: The Role of Definitions. Water International, 10, 111-120. https://doi.org/10.1080/02508068508686328
