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Rain-based factors of high agricultural impacts over Senegal. Part I: integration of local to sub-regional trends and variability

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Abstract

The evolution of seasonal cycle and interannual rainfall, the number of rainy days and daily rainfall types, dry spells frequency of occurrence, onset/cessation/length of rainy season, sowing dates, and the duration of the cropping period, are investigated at local (individual sites) and sub-regional scales (four different rainfall zones) using daily records of station data (83 sites) over Senegal. In the limits of a case study, these analyses complement and update previous studies conducted in the extreme Western Sahel (11–16° N and 20° W–10° E). The results unveil noticeable evolution of some of these rain-based factors in the recent periods as compared to the previous dry years. In the regions recording less than 800 mm/year (Sudan and Sahel sub-regions), the positive and statistically significant trends of rainfall amount are associated with new features of increasing frequency of short dry spell category, increasing number of some classes of extreme daily rainfall amounts and shifts in the peak number of rainy days. At sub-regional scales, the starting years (or change points) the magnitude and the signs of the new trends are unevenly distributed in the period post-1990. Earlier and higher amplitude changes are found at local scales and not less than one third of the sites in each sub-regional network are significantly affected. The extreme Southern sub-region exhibits no significant changes. Statistically significant trends are not observed on daily rain records ≤10 mm, onset/cessation dates, successful sowing dates, rainy season length, cropping period, medium and extreme dry spell categories. Rather, some of these factors such as the successful sowing date and the cropping season length exhibit significant variability. The onset (cessation) dates of the rainy season are followed (preceded) by extreme dry spell episodes. In the perspectives of climate impact assessments on the local agriculture a sub-regional periodic synopsis of the major rain-based factors of interest to agricultural applications are provided at the end the paper. They document some important internal variability patterns to reckon with in a multi-decadal work over the 1950–2008 period for this region.

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Notes

  1. The Technical Advisory Committee of the Consultative Group on International Agricultural Research

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Acknowledgments

The authors are indebted to Centre Régional pour l’Amélioration de l’Adapatation à la Sécheresse (CERAAS) and Agence Nationale de la Météorologie du Sénégal, (ANAMS) for providing rainguage data. Special regards to the various persons who manage and update the CERAAS database: Moustapha Fall, Couna Sylla, Cheikh Dramé, Benoit Sarr, Mbaye Diop, and Ndongo Ngom.

The first author acknowledges the German Academic Exchange Service (DAAD) for the In-Regions Scholarship through CERAAS (#A/09/04677). Fruitful discussions were held with Frédéric Hourdin. Comments and suggestions from Serge Janicot and an anonymous reviewer helped greatly improve the quality of this paper. Financial support was also provided by CIRAD and AMMA-EU in the framework of the AMMA project. Based on a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, UK, US, and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Research Program. Detailed information on scientific coordination and funding is available on the AMMA International web site. http://www.ammainternational.org.

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Authors and Affiliations

  1. Laboratoire de Physique de l’Atmosphère et de l’Océan Simeon Fongang, (LPAO-SF), Ecole Supérieure Polytechnique, Université Cheikh Anta Diop, BP 5085, Dakar-Fann, Dakar, Senegal

    S. Salack & A. T. Gaye

  2. Centre Régional pour l’Amélioration de l’Adaptation à la Sécheresse (CERAAS), BP 3320, Thiès Escale, Thiès, Senegal

    S. Salack

  3. Centre International de Recherche Agronomique pour le Développement (CIRAD), UMR, AGRAP, 34398, Montpellier, France

    B. Muller

  4. Africa Rice Center, AfricaRice, Sahel Regional Station, BP 96, Saint-Louis, Senegal

    B. Muller

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Correspondence to S. Salack.

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Salack, S., Muller, B. & Gaye, A.T. Rain-based factors of high agricultural impacts over Senegal. Part I: integration of local to sub-regional trends and variability. Theor Appl Climatol 106, 1–22 (2011). https://doi.org/10.1007/s00704-011-0414-z

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