The aim of this study is to highlight the combined effects of climate change and anthropization on surface waters in the Agnéby watershed. The global hydrological balances produced by the SWAT model show that in the year 2050, precipitation will record a deficit of 1.87%, while actual evapotranspiration will be 2.80% higher. Groundwater recharge and runoff will be in deficit by 2.5% and 9.77% respectively, and stock variation will be in deficit by 36.62% compared with the reference period. For 2080, precipitation, groundwater recharge and runoff will be in deficit by 1.23%, 1.5% and 10.23% respectively. Actual evapotranspiration will show an excess of 3.37%, and the change in stock relative to the reference period will also show a deficit of 20.42%. The hydrological consequence of this state of affairs is the depletion of surface water resources over the years in the Agnéby watershed due to anthropogenic activities. The predominance of evapotranspiration can be explained by the fact that the area will be covered by large-scale farming operations. These could also be explained by the fact that the area will be less favorable to surface runoff than to infiltration.
Soil erosion by precipitation, rainfall and runoff is a widespread phenomenon in different countries of the world. It becomes disastrous in particular on the slopes because of the torrentiality of the flow, of the strong vulnerability of the grounds (soft rocks, fragile grounds, steep slopes). The present study has for objective: The analysis of the data of concentrations of sediments in suspension are measured at the station of the rivers highlights relations, linking the concentration (or the solid flow) of the sediments in suspension to the liquid flow and to quantify the seasonal, monthly and interannual and intra annual variation of the surface degradation. Annual tonnage estimates of solids loads to the Mé were derived from the power law for all seasons. From this deduction, the annual quantities of sediment transported by the Mé from 2015/2017 is 7.06.106 t/year, or a specific degradation of 1.79.103 t/km2/year. On the other hand, in 2017, the value of this solid input is 3.06.106 t/year. However, the annual solid input is estimated at 7063.03.103 t/year with a specific degradation of 1784.47 t/km2/year at the Mé from 2015 to 2017.
This study aims to understand the influence of vegetation cover on the hydrological response of the Hana forest watershed. Using the GR2M hydrological model, hydroclimatic data over the 2000-2018 period were simulated to obtain real evapotranspiration (ETR), infiltration (I), and runoff (R). These different water balance terms were then correlated with a time series of NDVI extracted from MODIS-Terra (MOD13Q1) images over the period 2000-2018. The calibration of the hydrological model over the periods 1984-1989 and 2000-2018, respectively gave good Nash values of 74.1% and 64.6%. The validation, on the whole, gives satisfactory Nash values, except for the 1990-1999 one which is 56.4%. Cusum and t-student tests confirmed a significant break at α=5% in 2009 in the NDVI time series. Statistical analysis around this break date reveals a good correlation between NDVI and rainfall on the one hand and between NDVI and real evapotranspiration on the other hand, with respective correlation coefficients of 0.68, 0.66 for the sub-period 2000-2009. The relationship between NDVI and runoff is relatively weak there with a value of 0.38. Very high correlation coefficient values were obtained over the period 2010-2018 between NDVI and rainfall (0.78), between NDVI and real evapotranspiration (0.72) and between NDVI and runoff (0.68). However, low correlation coefficients of the order of 0.53 and - 0.07 were recorded between the NDVI and infiltration respectively before and after 2009.
The Aghien lagoon watershed is located in peripheral north-east areas of Abidjan. This space is accelerated population growth more than more important. The rate of urbanization is higher than 60% in 2014 (RGPH, 2014). Also, does the acceleration of urbanization result in vegetation cover degradation for the benefit of the built environment and a peri-urban agriculture. Also, does the acceleration of urbanization result in vegetation cover degradation for the benefit of the built environment and a peri-urban agriculture. This study aims to analyze in part one the diachronic evolution of vegetation cover between 1987-2000 and 2000-2015, and second part its takes stock of this dynamic between 1987 and 2015. Thus, the analysis of land use dynamics in the Aghien basin is based on the the vegetation mapping of landsat images. The methodology is based on the supervised classification by maximum likelihood of landsat images The results of the dynamics of land use in the basin in 1987, 2000 and 2015 indicate a decline in forest cover and perennial crops in favor of built environment and bare soil (+10.98%), subsistence crops and fallow (+11.37) over the period (1987-2015). Urbanization and increase crops are caused modifications of vegetation cover in outskirt of basin. These changes are mainly due to demographic pressure and unsustainable agricultural practics.
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