The population of northern Côte d'Ivoire, especially in the white Bandama watershed, lives for majority in rural areas and depends on farming, which is mainly linked to climate variability. This study evaluates the trends within watershed's hydro-climatic variables and their level of significance over the period 1950-2000. The methodological approach consists in applying successively standardized indexes to detect trends and breaks in hydro-climatic long-term data. The Mann-Kendall statistical test lets us know the trends significance and the Kendall-Theil Robust Line test reveals their magnitude. The Student's t test underlines break years. Results show that although rainfall has decreased, this decline is not statistically significant. However, temperature and potential evapotranspiration have strongly rised and discharge was submitted to high decline. These changes in hydrometeorological variables appeared from 1970 to 1980. This study is different from others conducted on climate variability in the northern Côte d'Ivoire by the methodological statistical framework implemented and the understanding of significance level of climate trends. Until now, authors used the standardized index to detect trends in hydro-climatic parameters. For this work, we added the Mann-Kendall statistical test to assess the significance level of these trends at α = 5% and 10%. Then, the Kendall-Theil statistical test was used to highlight the trends magnitude and the student's t test to know the break years.
La présente étude menée sur le bassin versant de la rivière Banco à Abidjan (5°20' et 5°26' de latitude Nord et entre 4°1'et 4°5' de longitude Ouest) dans le sud de la Côte d'Ivoire vise à mettre en exergue l'existence d'une variabilité climatique, à partir des fluctuations et des tendances dans les données hydroclimatiques (pluies, températures et débits). Pour atteindre cet objectif, diverses données (pluviométriques, thermométriques et hydrométriques) et méthodes (indice de Nicholson, tests de Cusum, de tstudent, de Mann-Kendall et de l'estimateur de la pente de Sen) ont été utilisées. A la lumière des résultats acquis, une variabilité climatique caractérisée par une alternance d'années humides, normales et sèches a été mise en évidence dans la zone d'étude. Les indices et méthodes statistiques montrent la continuité de la récession pluviométrique établie depuis 1970 avant une reprise pluviométrique à partir de l'année 2000. En ce qui concerne les températures, on assiste à une légère baisse de la température moyenne annuelle provoquée par la régression des températures minimales. La température moyenne dans le bassin versant a baissé de 1,4°C au cours des 34 dernières années. Les manifestations de cette variabilité climatique affectent peu le débit de la rivière. Une augmentation importante de l'écoulement superficielle apparaît dans le bassin avec un taux de changement de 71,25%, indiquant ainsi une bonne disponibilité en eau.
The objective of this study was to propose a mathematical regression model to estimate the exploitation flow rate of a water borehole from geophysical parameters in the midst of a fissured basement in the central-eastern part of Côte d'Ivoire. The data of the study are both hydrogeological and geophysical parameters from one hundred and eleven (111) data sheets of (111) water and geophysical boreholes. Two methods were used. The Normal Principal Component Analysis (NPCA) method applied to the data made it possible to select the explanatory variables (geophysical parameters) for borehole productivity. The multiple linear regression method subsequently made it possible to propose a mathematical model capable of estimating the exploitation rate from the geophysical parameters. The results indicate a very strong correlation (0.87) between longitudinal conductivity and flow rate, with flow rate and apparent resistivity negatively correlated. The multiple linear regression method highlighted two relevant explanatory variables, longitudinal conductivity and apparent resistivity. These two geophysical parameters contributed to a mathematical model in the form
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