Impact of Land use Dynamics on Runoff in the Agnéby Watershed, South-Eastern Ivory Coast

This research work appears to be useful for understanding phenomena such as the impact of land use dynamics on surface runoff from one period to another. Located in the south-east of Côte d'Ivoire, the Agnéby catchment area, with a surface area of 8640 km2, has undergone changes in its vegetation cover between the periods 1988-2020. These changes have resulted in the regression of dense forest with a loss of 53% to the benefit of crops and fallow land with a gain of 41%. Bare soil and water habitats have increased by 5% and 2% of the total area of the basin. During the same period, the annual retention capacity indexes fell from 162.08 in 1998 to 102.56 in 2020 with an annual regression rate of 0.38. On the other hand, the average annual runoff coefficients have increased from 12.80% to 23.77%. In the near and distant future, the Agnéby area will experience a form of degradation in view of its rapid economic growth, where there is no policy of sustainable management of natural resources. In this context, crops and fallow land and bare soil habitats will be dominant and will occupy proportions of 64.56% and 12.40% respectively in 2050 and 67.20% and 14.33% in 2080. For these same horizons, the retention capacity indices will be 94.48 and 90.51 in 2050 and 2080 respectively. The annual runoff coefficients will be 25.66 in 2050 and 26.70 in 2080. These different values of the retention capacity indices and runoff coefficients show that the basin has experienced and will experience a strong degradation under the scenario of rapid economic growth. Decision-makers and stakeholders in charge of territorial management must therefore take these results into account in their decision-making. The values of the runoff indices and coefficients show the total anthropisation of the Agnéby catchment area and the impact of the dynamics on the surface runoff in the near and distant future