Reply to comment on ‘Long-term rise in a Sahelian water-table: the Continental Terminal in South-West Niger’ by Leduc, C., Favreau, G., Schroeter, P., 2001. Journal of Hydrology 243, 43–54

Favreau, Guillaume; Leduc, Christian; Schroeter, Pierre

doi:10.1016/s0022-1694(01)00517-0

Cited by 12 publications

(8 citation statements)

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“…Our hydrological simulations evidence the dominant effect of past environment changes over climate change on runoff in the Wankama catchment, in agreement with available signs of runoff increase in the area (Favreau, 2000;Favreau et al, 2002b;Leduc and Loireau, 1997;Leduc et al, 2001). If only environmental changes are considered, i.e.…”

Section: Discussionsupporting

confidence: 85%

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

Séguis

Cappelaere

Milesi

et al. 2004

Hydrological Processes

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In the Sahel, there are few long-term data series available to estimate the climatic and anthropogenic impacts on runoff in small catchments. Since 1950, land clearing has enhanced runoff. The question is whether and by how much this anthropogenic effect offsets the current drought. To answer this question, a physically based distributed hydrological model was used to simulate runoff in a small Sahelian catchment in Niger, from the 1950-1998 rain-series. The simulation was carried out for three soil surface states of the catchment (1950, 1975 and 1992). The catchment is characterized by an increase in cultivated land, with associated fallow, from 6% in 1950 to 56% in 1992, together with an increase in the extent of eroded land (from 7 to 16%), at the expense of the savanna. Effects of climate and land use are first analysed separately: irrespective of the land cover state, the simulated mean annual runoff decreases by about 40% from the wet period (1950-1969) to the dry period (1970-1998); calculated on the 1950-1998 rainfall-series, the changes that occurred in land cover between 1950 and 1992 multiplies the mean annual runoff by a factor close to three. The analysis of a joint climatic and anthropogenic change shows that the transition from a wet period under a 'natural' land cover (1950) to a dry period under a cultivated land cover (1992) results in an increase in runoff of the order of 30 to 70%. At the scale of a small Sahelian catchment, the anthropogenic impact on runoff is probably more important than that of drought. This figure for relative increase in runoff contributions to ponds, preferential sites of seepage to groundwater, is less than that currently estimated for aquifer recharge, which has been causing a significant continuous water table rise over the same period. Copyright (C) 2004 John Wiley Sons, Ltd

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Section: Discussionsupporting

confidence: 85%

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

Séguis

Cappelaere

Milesi

et al. 2004

Hydrological Processes

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“…Fluctuations of the nitrate content (NO 3 ‐N) and groundwater level recorded during the 1997–2001 period (Maourey Kouara Zeno) [after Favreau et al , 2004b]. Screen depth is 21 to 24 m.…”

Section: Resultsmentioning

confidence: 99%

Land clearing, climate variability, and water resources increase in semiarid southwest Niger: A review

Favreau

Cappelaere

Massuel

et al. 2009

Water Resources Research

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235

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The water table in southwestern Niger has been rising continuously for the past decades (4 m rise from 1963 to 2007), despite a ∼23% deficit in monsoonal rainfall from 1970 to 1998. This paradoxical phenomenon has been linked with a change in land use from natural savannah to millet crops that have expanded in area sixfold since 1950 and have caused soil crusting on slopes that has, in turn, enhanced Hortonian runoff. Runoff concentrates in closed ponds and then recharges the aquifer; therefore, higher runoff increases aquifer recharge. At the local scale (2 km2), a physically based, distributed hydrological model showed that land clearing increased runoff threefold, whereas the rainfall deficit decreased runoff by a factor of 2. At a larger scale (500 km2, 1950–1992 period), historical aerial photographs showed a 2.5‐fold increase in the density of gullies, in response to an 80% decrease in perennial vegetation. At the scale of the entire study area (5000 km2), analytical modeling of groundwater radioisotope data (3H and 14C) showed that the recharge rate prior to land clearing (1950s) was about 2 mm a−1; postclearing recharge, estimated from groundwater level fluctuations and constrained by subsurface geophysical surveys, was estimated to be 25 ± 7 mm a−1. This order of magnitude increase in groundwater fluxes has also impacted groundwater quality near ponds, as shown by a rising trend in groundwater nitrate concentrations of natural origin (75% of δ15N values in the range +4 to +8‰). In this well‐documented region of semiarid Africa, the indirect impacts of land use change on water quantity and quality are much greater than the direct influence of climate variability.

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“…2). Interdrainage (direct) recharge might also occur, although dedicated studies have failed to show any deep infiltration below a few meters in depth below the soil surface (Favreau et al, 2002b;Massuel et al, 2006).…”

Section: Study Area and Backgroundmentioning

confidence: 99%

Land clearance and hydrological change in the Sahel: SW Niger

Leblanc

Favreau

Massuel

et al. 2008

Global and Planetary Change

197

170

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Reply to comment on ‘Long-term rise in a Sahelian water-table: the Continental Terminal in South-West Niger’ by Leduc, C., Favreau, G., Schroeter, P., 2001. Journal of Hydrology 243, 43–54

Cited by 12 publications

References 13 publications

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

Simulated impacts of climate change and land‐clearing on runoff from a small Sahelian catchment

Land clearing, climate variability, and water resources increase in semiarid southwest Niger: A review

Land clearance and hydrological change in the Sahel: SW Niger

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