Étude De La Variabilité Hydroclimatique Et De Ses Conséquences Sur Les Ressources En Eau Du Sud Forestier Et Agricole De La Côte d'Ivoire : Cas De La Région d'Abidjan-Agboville
Kouassi Ernest AHOUSSI, Yao Blaise KOFFI, Amani Michel KOUASSI, Gbombélé SORO, Nagnin SORO, et Jean BIÉMI

Climate variability observed since the 1970s has resulted in a drought last thirty years in West Africa in general and in the Sahelian and humid countries bordering the Gulf of Guinea. It results in severe reductions in rainfall, groundwater levels and stream flows drop of water. In order to examine the existence of the climate variability in Côte d'Ivoire, precisely in the region of Abidjan-Agboville, and highlight its impact on the supply of water, that this study was initiated. To do this, various data and methods were used. Thus, the methodology involves the calculation of centered reduced indices of NICHOLSON, testing PETTIT, the Bayesian method of LEE and HEGHINIAN and Segmentation of HUBERT. The region is marked by alternating normal period, wet and dry, with a long period deficit starting from 1970. The rainfall deficit is between 10 % and 31%, with an average value of 20 %. The largest deficits were recorded in the southern region, including Alépé (31 %), Adiaké (25 %) and Abidjan (20 %). Hydrological regimes have also undergone profound changes over the period 1955- 2003. The decline in rainfall has resulted in a reduction of water supplies that pass through the rivers of the region. This decrease is marked by a very significant breach identified in 1968 at the Agboville station on the river Agnéby. The lack of flow is very important and is estimated at 41.3 %, double the rainfall deficit (20 %). At the river Agnéby, coefficients of drying of MAILLET (with flow en m3 s-1 and time in days) are changing from 0.0314 to 0.106 before 1968 and from 0.0367 to 0.124 after 1968. This increase in the coefficient of drying after 1968 shows a much faster draining aquifers supplying base flow. The mean values ranged from 0.065 before 1968 and 0.0814 after this year. The volume of water mobilized aquifer rises to 0.143 km3 for an average depletion coefficient of 6.53 during the period 1956- 1968 and 0.058 km3 for a coefficient of drying average of 0.0814 from 1969 to 2003. Volumes mobilized aquifer after 1968 fell 59.45 %, resulting in a considerable reduction of groundwater reserves. The fluctuation of rainfall isohyets shows that 2300 mm and 2200 mm in the region during the decade 1950-1959 have disappeared to make room for 1500 mm isohyets during the decade 1990-1999.

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