Caractérisation des saisons de pluies au Burkina Faso dans un contexte de changement climatique et évaluation des impacts hydrologiques sur le bassin du Nakanbé

Abstract : This study aims to a description of the variability in the rainfall regime over the West African Sahel and an assessment of the impacts of this variability on the water resources in the region from a set of some hydrological models. Although, many results of some studies on rainfall variability over Sahel during the last five decades (1961-2009) show a significant decrease in the annual rainfall amount since 1970. This rainfall deficit has entailed a severe hydric stress in the region. Burkina Faso, a sahelian country, is under this situation of continuous drought condition. So, to characterize the climate condition at the scale of Burkina Faso, we analyzed the rainfall data of the synoptic network through a discretization of the rainy seasons in several characteristics relative to the season period, rainfall frequency and intensity, and the dry spells. A computation of these characteristics from observed rainfall data and from simulated rainfall data of five regional climate models (CCLM, HadRM3P, RACMO, RCA et REMO) run under scenario A1B of IPCC, helped to assess the representativeness of the simulations over Burkina Faso. Indeed, the simulated rainfall data present high frequency of low rainfalls (between 0.1 mm/day and 5 mm/day), and some heavy maximum daily rainfall. However, an application of a correction procedure, quantile-quantile, to the simulated rainfall, significantly reduced the different biases and produced some rainfall data similar to the observations over the 1961-2009 period. An analysis of the future variability of rainfall regime over the prediction period of 2021-2050 in comparison to the reference period of 1971-2000 and from the five climate models presents different tendencies in the evolution of the annual rainfall amount: two models predict significant decrease in rainfall while two others predict a significant increase in the annual rainfall amount. These significant changes come from a decrease in rainfall frequency or an increase in rainfall intensity. However, two consensuses come out from the models: a decrease in the very low rainfall (0.1 à 5 mm/jr) and a lengthening of the mean dry spell. Also, four models show an increase in the very strong rainfall (>50 mm/day). On the other hand, the five models show an increasing trend in the potential evapotranspiration (PET) over the 1961-2050 period. The impacts of these changes in rainfall regime and the increase in the PET on the hydrological regime of the sahelian part of Nakanbé basin in Burkina Faso (upstream of the Wayen gauge) are assessed from two hydrological models, GR2M and ORCHIDEE. The GR2M, calibrated and validated for the basin over the 1978-1999 period, reproduced the hydrological balance of the basin during this period. But for ORCHIDEE, a repartition procedure was elaborated in order to distribute the simulated runoff into the discharges and infiltrations. So, an implementation of these hydrological models under the climate change conditions of rainfall decrease shows an hydrological constraint with a decrease in the runoff and the water table recharge, and an increase in the evaporation rate in the hydrological balance of the basin. However, the amplitude of the hydrological impacts depends on the type of the change in the main characteristics of the rainy season: in the rainfall frequency or in the rainfall intensity. So, a decrease in the rainfall intensity is more prejudicial to water resources availability with an important increase in the evaporation rate and an important decrease in the runoff and in the groundwater recharge.
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  • HAL Id : tel-00827764, version 1

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Boubacar Ibrahim. Caractérisation des saisons de pluies au Burkina Faso dans un contexte de changement climatique et évaluation des impacts hydrologiques sur le bassin du Nakanbé. Hydrologie. Université Pierre et Marie Curie - Paris VI, 2012. Français. ⟨NNT : 2012PA066087⟩. ⟨tel-00827764⟩

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