Modelling groundwater recharge, actual evaporation and transpiration in semi-arid sites of the Lake Chad Basin: The role of soil and vegetation on groundwater recharge

Abstract. The Lake Chad Basin, located in the center of North Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential evapotranspiration. Groundwater is an essential source for drinking water supply as well as for agriculture and groundwater related ecosystems. Thus, assessment of groundwater recharge is very important although difficult, because of the strong effects of evaporation and transpiration as well as limited available data. A simple, generalized approach, which requires only a small number of field data, freely available remote sensing data as well as well-established concepts and models, is tested for assessing groundwater recharge in the southern part of the basin. This work uses the FAO-dual Kc concept to estimate E and T coefficients at six locations that differ in soil texture, climate, and vegetation conditions. Measured values of soil water content and chloride concentrations along vertical soil profiles together with different scenarios for E and T partitioning and a Bayesian calibration approach are used to numerically simulate water flow and chloride transport. Average groundwater recharge rates and the associated model uncertainty at the six locations are assessed for the 2003–2016 time-period. Model results show that interannual variability of groundwater recharge is generally greater than the uncertainty of the modelled groundwater recharge. Furthermore, the soil moisture dynamics at all locations are limited rather by water availability for evaporation in the uppermost part of the soil and by water uptake in the root zone than by the reference evapotranspiration.

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Modelling groundwater recharge, actual evaporation and transpiration in semi-arid sites of the Lake Chad Basin: The role of soil and vegetation on groundwater recharge

10.5194/hess-2021-390 ◽

2021 ◽

Author(s):

Christoph Neukum ◽

Angela Gabriela Morales Santos ◽

Melanie Ronelngar ◽

Sara Vassolo

Keyword(s):

Groundwater Recharge ◽

Root Zone ◽

Chloride Transport ◽

Potential Evapotranspiration ◽

Remote Sensing Data ◽

Lake Chad ◽

Chad Basin ◽

Time Period ◽

Lake Chad Basin ◽

Potential Groundwater

Abstract. The Lake Chad Basin, located in the center of North Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential evapotranspiration. Groundwater is an essential source for drinking water supply as well as for agriculture and groundwater related ecosystems. Thus, assessment of groundwater recharge is very important although difficult, because of the strong effects of evaporation and transpiration as well as limited available data. A simple, generalized approach, which requires only a small number of field data, freely available remote sensing data, and well-established concepts and models, is tested for assessing groundwater recharge in the southern part of the basin. This work uses the FAO-dual Kc concept to estimate E and T coefficients at six locations that differ in soil texture, climate, and vegetation conditions. Measured values of soil water content and chloride concentrations along vertical soil profiles at these locations together with different scenarios for E and T partitioning and a Bayesian calibration approach are used to numerically simulate water flow and chloride transport. Average potential groundwater recharges and the associated model uncertainty at the six locations are assessed for the time-period 2003–2016. Model results show that interannual variability of groundwater recharge is generally higher than the uncertainty of the modelled groundwater recharge. Furthermore, the soil moisture dynamics at all locations are limited by water availability for evaporation in the uppermost part of the soil and by water uptake in the root zone rather than by the reference evapotranspiration.

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Biomass Burning and Water Balance Dynamics in the Lake Chad Basin in Africa

Earth ◽

10.3390/earth2020020 ◽

2021 ◽

Vol 2 (2) ◽

pp. 340-356

Author(s):

Forrest W. Black ◽

Jejung Lee ◽

Charles M. Ichoku ◽

Luke Ellison ◽

Charles K. Gatebe ◽

...

Keyword(s):

Water Balance ◽

Biomass Burning ◽

Water Cycle ◽

Potential Evapotranspiration ◽

Southern Oscillation ◽

Wet Season ◽

Lake Chad ◽

Chad Basin ◽

Lake Chad Basin ◽

Logone Catchment

The present study investigated the effect of biomass burning on the water cycle using a case study of the Chari–Logone Catchment of the Lake Chad Basin (LCB). The Chari–Logone catchment was selected because it supplies over 90% of the water input to the lake, which is the largest basin in central Africa. Two water balance simulations, one considering burning and one without, were compared from the years 2003 to 2011. For a more comprehensive assessment of the effects of burning, albedo change, which has been shown to have a significant impact on a number of environmental factors, was used as a model input for calculating potential evapotranspiration (ET). Analysis of the burning scenario showed that burning grassland, which comprises almost 75% of the total Chari–Logone land cover, causes increased ET and runoff during the dry season (November–March). Recent studies have demonstrated that there is an increasing trend in the LCB of converting shrubland, grassland, and wetlands to cropland. This change from grassland to cropland has the potential to decrease the amount of water available to water bodies during the winter. All vegetative classes in a burning scenario showed a decrease in ET during the wet season. Although a decrease in annual precipitation in global circulation processes such as the El Niño Southern Oscillation would cause droughts and induce wildfires in the Sahel, the present study shows that a decrease in ET by the human-induced burning would cause a severe decrease in precipitation as well.

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