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L'article du mois ( avril 2017)

Variability and trends of wet season temperature in the Sudano-Sahelian zone and
relationships with precipitation

Boutheina Oueslati, Pierre Camberlin, Joël Zoungrana, Pascal Roucou, Saliou Diallo (2017) Climate Dynamincs, in press.












Tendances mensuelles et annuelles des températures maximales au Burkina-Faso (1959-2008), en degrés par décennie. Rouge plein : données brutes, tirets rouges : après déduction de l’effet des précipitations. En bas : tendances des précipitations.

 The relationships between precipitation and temperature in the central sudano-sahelian belt are investigated by analyzing 50 years (1959-2008) of observed temperature (Tx and Tn) and rainfall variations. At daily time-scale, both Tx and Tn show a marked decrease as a response to rainfall occurrence, with a strongest departure from normal one day after the rainfall event (-0.5 to -2.5°C depending on the month).

The cooling is slightly larger when heavy rainfall events (> 5mm) are considered. The temperature anomalies weaken after the rainfall event, but are still significant several days later. The Tx drop is  accounted for by reduced incoming solar radiation associated with increased cloud cover and increased surface evaporation following surface moistening. The effect of evaporation becomes dominant a few days after the rainfall event. The reduced daytime heat storage and the subsequent sensible heat flux result in a later negative Tn anomaly. The effect of rainfall variations on temperature is significant for long-term warming trends. The rainfall decrease experienced between 1959 and 2008 accounts for a rainy season Tx increase of 0.15 to 0.3°C, out of a total Tx increase of 1.3 to 1.5°C. These results have strong implications on the assessment of future temperature changes. The dampening or amplifying effects of precipitation are determined by the sign of future precipitation trends. Confidence on temperature changes under global warming partly depend on the robustness of precipitation projections.



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