Chapitre 7. Facteurs anthropiques et environnementaux de la recrudescence des inondations au Sahel

Descroix, Luc; Mahé, Gil; Olivry, Jean-Claude; Albergel, Jean; Tanimoun, Bachir; Amadou, Ilia; Coulibaly, Bréhima; Moussa, Ibrahim Bouzou; Maïga, Oumarou Faran; Abdou, Moussa Malam; Yéro, Kadidiatou Souley; Mamadou, Ibrahim; Vandervaere, Jean‐Pierre; Gautier, Emmanuèle; Diongue-Niang, Aïda; Dacosta, Honoré; Diedhiou, Arona

doi:10.4000/books.irdeditions.9080

Cited by 6 publications

(12 citation statements)

References 23 publications

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“…• Rainfall decadal variability induces land cover changes, such as ligneous vegetation dying, due to severe drought; this vegetation cover reduction could, in time, explain the increasing runoff and discharges; • Some studies ( [2,78,87,95,104] among others) have demonstrated that the re-greening does not prevent the increase in runoff and in basin discharge, due to the severe degradation of small parts of these basins, generally located near the "kori". The intensification of rainfall began in the middle of the 1980s, but it reached its maximum in the middle of the 2001-2010 decade [4,7].…”

Section: Main Trends Described In Recent Workmentioning

confidence: 99%

“…This "erosion-crusting" mainly concerns newly cropped typical Sahelian sandy soils and is most often assumed to be a consequence of land clearing and extension of cropping [6,93,94] (land use change). In pastoral areas, during the drought, the removal of the thin lithosol by wind or water erosion, occurring because of the vegetation dying, led rocks to outcrop [16,49,72,95] (land cover change).…”

Section: Highlighting the Correlation Between Land Use/land Cover Andmentioning

confidence: 99%

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Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Descroix

Guichard

Grippa

et al. 2018

Water

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Abstract:In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968-1990s 'Great Drought' period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity.

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Section: Main Trends Described In Recent Workmentioning

confidence: 99%

Section: Highlighting the Correlation Between Land Use/land Cover Andmentioning

confidence: 99%

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Descroix

Guichard

Grippa

et al. 2018

Water

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“…Olivry (2002, personal communication cited in [59]) also proposed that the Sudanian regions are dominated by an excess of a saturation-based runoff process (Hewlettian) rather than by refusal of infiltration (Hortonian) as in the Sahelian regions (arid and semi-arid). Considering that the soil's water holding capacity is fairly constant, the flow deficit is even greater given that a large part of the water retained by the soil is transpired through vegetation [25]. The increase in evapotranspiration thus exacerbates the effect of the declining rainfall on streamflows.…”

Section: The 1970 Drought and Its Hydrological Impactsmentioning

confidence: 99%

“…However, large systems such as the Niger and Senegal rivers, whose flow comes essentially from the Sudanian region, have been heavily impacted by drought and their flow rates have clearly decreased [25,26]. In the Sudanian zone, the flow rates have clearly decreased in a higher proportion than rainfall [25,27]. Several authors argue that this significant decrease is mainly due to a significant decrease in base flow that is in turn due to a decline in water table [27,28].…”

Section: Introductionmentioning

confidence: 99%

“…The flow increase is linked to the increase of the groundwater level observed in endorheic catchments such as in Southwestern Niger, due to the accumulation of runoff water in depressions [23,24]. However, large systems such as the Niger and Senegal rivers, whose flow comes essentially from the Sudanian region, have been heavily impacted by drought and their flow rates have clearly decreased [25,26]. In the Sudanian zone, the flow rates have clearly decreased in a higher proportion than rainfall [25,27].…”

Section: Introductionmentioning

confidence: 99%

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Climate Variability and Groundwater Response: A Case Study in Burkina Faso (West Africa)

Tirogo

Jost

Biaou

et al. 2016

Water

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West Africa experiences great climate variability, as shown by the long-lasting drought since the 1970s. The impacts of the drought on surface water resources are well documented but remain less studied regarding groundwater resources. The nexus between climate variability and groundwater level fluctuations is poorly documented in this area. The present study focuses on the large reserve of groundwater held by the Kou catchment, a tributary of Mouhoun river (formerly the Black Volta) in the southwest of Burkina Faso, in the Sudanian region. Analyses were undertaken using climatic time series , two rivers' hydrometric data , and 21 piezometers' time series (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) applying statistical trend (Mann-Kendall) and break (Pettitt) tests, correlation analysis, and principal component analysis. The analyses showed that rainfall in the area underwent a significant break in 1970 with an 11%-16% deficit between the period before the break and the period after the break that resulted in a deficit three times greater for both surface and base flows. This significant deficit in flow results from the combined effect of a decrease in rainfall and an increase in evapotranspiration. The response of the catchment to the slight increase in rainfall after 1990 was highly dependent on hydrological processes. At Samendéni, on the Mouhoun River, the flow increased with a slight delay as compared to rainfall, because of the slow response of the base flow. Whereas at Nasso on the Kou river, the flow steadily decreased. The analysis showed that the groundwater level responds to rainfall with a delay. Its response time to seasonal fluctuations ranges from 1 to 4 months and its response time to interannual variations exceeds the timescale of one year. This response is highly dependent on the local aquifer's physical characteristics, which could explain the spatial heterogeneity of the groundwater response.

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Improving Public Action to Mitigate River Flooding in Niamey (Niger)

Mahamane,

Oumarou,

Piñeira Mantiñán

2023

Land

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The purpose of this paper is to analyze the effects of repeated floods in the city of Niamey and the strategies developed by the state in terms of prevention, rehabilitation, and care for victims. Although numerous framework documents have been drafted in the last decade and urbanization in flood zones has been limited, the reality in Niamey shows that urban sprawl is increasing along the riverbank and the population facing vulnerable situations is growing. The inefficiency of state action determines that, on the one hand, it is non-governmental institutions that need to develop improvement plans—with the recovery of the city being dependent on the arrival of their funds and their distribution in those areas that donor countries consider most suitable—and on the other hand, it is the citizens—already vulnerable—who must find their own resilience mechanisms to try to survive the next flood. This study reveals that this diversity of players is involved in flood management through emergency relief, solidarity in rehousing, and providing support for living and non-living flood victims. Despite this mobilization, the actions undertaken are hampered by a number of constraints. Insufficient financial and human resources, a lack of foresight on the part of the authorities, and poorly coordinated actions are the main difficulties limiting the success of public action in the face of flooding. Through a qualitative approach, combining documentary research, direct observation and semi-structured interviews, we analyze the mobilization of actors around the management of the effects of floods in Niamey.

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Chapitre 7. Facteurs anthropiques et environnementaux de la recrudescence des inondations au Sahel

Cited by 6 publications

References 23 publications

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

Climate Variability and Groundwater Response: A Case Study in Burkina Faso (West Africa)

Improving Public Action to Mitigate River Flooding in Niamey (Niger)

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