The shallow aquifer in the Lake Chad basin is highly vulnerable to pollution. Analysis carried ou... more The shallow aquifer in the Lake Chad basin is highly vulnerable to pollution. Analysis carried out on 316 wells and boreholes have showed a tendency towards an increase of nitrate values, exceeding 50 mg l−1. Nitrate concentrations ranged between about 1 and 300 mg l−1. Large variation in concentration was observed in wells and boreholes that are only short distances apart. High concentrations of nitrate in wells, especially in a recharge area along the sand dunes, or via infiltration from river banks, irrigation channels, and infiltration of urban wastewater into groundwater from septic tanks, pose a serious problem for drinking water supply. In Cameroon and Chad, the results of the investigation indicate a variation of nitrate concentration in groundwater between the two areas. The primary origin of this pollution is agricultural proliferation activities that are developed and stressed by socio-economic needs outside the urban area, and by urban expansion within the area served by...
The scarcity of groundwater storage change data at the global scale hinders our ability to monito... more The scarcity of groundwater storage change data at the global scale hinders our ability to monitor groundwater resources effectively. In this study, we assimilate a state-of-the-art terrestrial water storage product derived from Gravity Recovery and Climate Experiment (GRACE) satellite observations into NASA's Catchment land surface model (CLSM) at the global scale, with the goal of generating groundwater storage time series that are useful for drought monitoring and other applications. Evaluation using in situ data from nearly 4,000 wells shows that GRACE data assimilation improves the simulation of groundwater, with estimation errors reduced by 36% and 10% and correlation improved by 16% and 22% at the regional and point scales, respectively. The biggest improvements are observed in regions with large interannual variability in precipitation, where simulated groundwater responds too strongly to changes in atmospheric forcing. The positive impacts of GRACE data assimilation are further demonstrated using observed low-flow data. CLSM and GRACE data assimilation performance is also examined across different permeability categories. The evaluation reveals that GRACE data assimilation fails to compensate for the lack of a groundwater withdrawal scheme in CLSM when it comes to simulating realistic groundwater variations in regions with intensive groundwater abstraction. CLSM-simulated groundwater correlates strongly with 12-month precipitation anomalies in low-latitude and midlatitude areas. A groundwater drought indicator based on GRACE data assimilation generally agrees with other regional-scale drought indicators, with discrepancies mainly in their estimated drought severity.
The shallow aquifer in the Lake Chad basin is highly vulnerable to pollution. Analysis carried ou... more The shallow aquifer in the Lake Chad basin is highly vulnerable to pollution. Analysis carried out on 316 wells and boreholes have showed a tendency towards an increase of nitrate values, exceeding 50 mg l−1. Nitrate concentrations ranged between about 1 and 300 mg l−1. Large variation in concentration was observed in wells and boreholes that are only short distances apart. High concentrations of nitrate in wells, especially in a recharge area along the sand dunes, or via infiltration from river banks, irrigation channels, and infiltration of urban wastewater into groundwater from septic tanks, pose a serious problem for drinking water supply. In Cameroon and Chad, the results of the investigation indicate a variation of nitrate concentration in groundwater between the two areas. The primary origin of this pollution is agricultural proliferation activities that are developed and stressed by socio-economic needs outside the urban area, and by urban expansion within the area served by...
The scarcity of groundwater storage change data at the global scale hinders our ability to monito... more The scarcity of groundwater storage change data at the global scale hinders our ability to monitor groundwater resources effectively. In this study, we assimilate a state-of-the-art terrestrial water storage product derived from Gravity Recovery and Climate Experiment (GRACE) satellite observations into NASA's Catchment land surface model (CLSM) at the global scale, with the goal of generating groundwater storage time series that are useful for drought monitoring and other applications. Evaluation using in situ data from nearly 4,000 wells shows that GRACE data assimilation improves the simulation of groundwater, with estimation errors reduced by 36% and 10% and correlation improved by 16% and 22% at the regional and point scales, respectively. The biggest improvements are observed in regions with large interannual variability in precipitation, where simulated groundwater responds too strongly to changes in atmospheric forcing. The positive impacts of GRACE data assimilation are further demonstrated using observed low-flow data. CLSM and GRACE data assimilation performance is also examined across different permeability categories. The evaluation reveals that GRACE data assimilation fails to compensate for the lack of a groundwater withdrawal scheme in CLSM when it comes to simulating realistic groundwater variations in regions with intensive groundwater abstraction. CLSM-simulated groundwater correlates strongly with 12-month precipitation anomalies in low-latitude and midlatitude areas. A groundwater drought indicator based on GRACE data assimilation generally agrees with other regional-scale drought indicators, with discrepancies mainly in their estimated drought severity.
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