Application of a Deterministic Distributed Hydrological Model for Estimating Impact of Climate Change on Water Resources in Côte d’Ivoire Using RCP 4.5 and RCP 8.5 Scenarios: Case of the Aghien Lagoon

International audienceThis work aims to evaluate the impact of climate change on the quantitative availability of the Aghien lagoon located in the north of the Abidjan district in Côte d'Ivoire. In first step, the semi-distributed SWAT (Soil and Water Assessment Tools) based physical model [1] was calibrated and validated at the monthly time step over the period 1960-1981, in the Mé watershed where flow rates data are available. SWAT was then applied on the watershed of the lagoon of Aghien which is ungauged but for which the challenges are considerable for the drinking water supply of the Abidjanese population. In a second step, the gross outputs (precipitation, temperatures) of six climate models of the CORDEX-Africa project under the "Representative Concentration Pathways" (RCP 4.5 and RCP 8.5) scenarios were corrected using the delta method. These corrected outputs were used at the SWAT model input to project the impact of climate change on the flow of the Aghien lagoon for horizons 2040 (2035-2056), 2060 (2057-2078) and 2080 (2079-2100). The projections made on these different horizons were compared with the simulated flow over the period 1960-1981. The results show a sensible decrease in the annual flow of the Aghien lagoon compared to the reference period (1960-1981). Under the medium assumption (RCP 4.5), the models predict a decrease in the annual discharge almost 10% on average. Under the pessimistic hypothesis (RCP 8.5), the average annual discharge should decrease by more than 17%. On a monthly basis, flows in August and September would increase by more than 80% and those in October and November would increase by more than 20% in both RCP scenarios

Estimation of the Impact of Climate Change on Water Resources Using a Deterministic Distributed Hydrological Model in Côte d’Ivoire: Case of the Aghien Lagoon

International audienceThis work aims to evaluate the impact of climate change on the quantitative availability of the Aghien lagoon located in the north of the Abidjan district in Cô ;te d’Ivoire. In the first step, the semi-distributed SWAT (Soil and Water Assessment Tools) based physical model (Arnold et al., 1998) was calibrated and validated at the monthly time step over the period 1960-1981, in the Me watershed for which data from flow rates are available. SWAT was then applied on the watershed of the lagoon of Aghien which is ungauged but for which the challenges are considerable for the drinking water supply of the Abidjanese population. In the second step, the gross outputs (precipitation, temperatures) of six climate models of the CORDEX-Africa project under the “Representative Concentration Pathways” (RCP 4.5 and RCP 8.5) scenarios were corrected using the delta method. These corrected outputs were used at the SWAT model input to project the impact of climate change on the flow of the Aghien lagoon to horizons 2040 (2035-2056), 2060 (2057-2078) and 2080 (2079-2100). The projections made on these different horizons were compared with the simulated flow over the period 1960-1981. The results show a sensible decrease in the annual flow of the Aghien lagoon compared to the reference period (1960-1981). Under the medium assumption (RCP 4.5), the models predict a decrease in the annual discharge almost 10% on average. Under the pessimistic hypothesis (RCP 8.5), the average annual discharge should decrease by more than 17%. On a monthly basis, flows in August and September would increase by more than 80% and those in October and November would increase by more than 20% in both RCP scenarios

Application of Swat to estimate water balance in the Aghien lagoon basin, South-East of Ivory Coast.

International audienc

Assessment of the Potential Pollution of the Abidjan Unconfined Aquifer by Hydrocarbons

A study of the unconfined Continental Terminal aquifer in Abidjan District, located in a coastal sedimentary basin in Southern Côte d’Ivoire (West Africa), is conducted. This aquifer is the principal source of drinking water for the city of Abidjan. The water quality of the aquifer is affected by anthropogenic sources of pollution, such as scattered deposits of solid and liquid waste of all kinds. Additionally, the proliferation of gas stations, including potential tank leakage, must be considered in the event of an accident. To ensure the effective protection and management of the Abidjan groundwater, this work assesses the groundwater contamination risk of the Abidjan aquifer by hydrocarbons such as benzene. To achieve this objective, a numerical groundwater model that included the geological and hydrogeological data of the Abidjan aquifer was constructed with FEFLOW 7.1. A predictive simulation of groundwater flow coupled with the transport of dissolved benzene deposited on the soil surface at the N’Dotré and Anador gas stations was performed. The initial concentrations of dissolved benzene were 43.12 mg/L and 14.17 mg/L at the N’Dotré and Anador sites, respectively. The results revealed that a threshold concentration of 0.001 mg/L was reached after 44 years and two months at borehole ZE11, which is located four kilometers downgradient from the source. The maximum peak concentration of 0.011 mg/L was reached at this point after 47 years and two months. In this region, 14 other boreholes could be threatened by dissolved benzene pollution based on the simulation

Global Change in Africa

The main objective of this book is to provide an overview of the benefit of using Earth Observation data to monitor global environmental changes due to natural phenomena and anthropogenic forcing factors over the African continent, and highlight a number of applications of high societal relevance.The main topics presented in the book concern: water resources, floods and droughts, coastal zones changes and exploitation of mineral resources and its impact on the environment

Artisanal Exploitation of Mineral Resources: Remote Sensing Observations of Environmental Consequences, Social and Ethical Aspects

International audienceSince the rise of the gold price in 2000, artisanal and small-scale gold mining (ASGM) is a growing economic activity in developing countries. It represents a source of income for several millions of people in West Africa. Exploitation techniques have evolved from traditional gold panning to mechanization and use of chemical products that are harmful for the environment. Government strategies to control and regulate this activity are impeded by the difficulties to collect spatial information, due to the remote location and the mobile and informal natural of ASGM. Here we present and discuss the value of remote sensing techniques to complement the knowledge on artisanal mining impacts, including for detection of illegal sites, the evaluation of the degradation of soils and waters, the deforestation and the monitoring of expansion of ASGM with time. However, these techniques are blind regarding gender issues, labor relations, mobility, migration, and insecurity and need to be considered with knowledges from other disciplines. Remote sensing is also instilled with various powers accruing to those enabled to produce and interpret these data. Remote sensing should be therefore used in a reflexive manner that accounts for the social, ethical and political implications of ASGM governance informed by space observations