Cartographie par télédétection des variations spatio-temporelles de la couverture végétale spontanée face à la variabilité pluviométrique au Sahel : approche multiscalaire

Marega, Oumar; Emeterio, José-Luis San; Fall, Ababacar; Andrieu, Julien

doi:10.4000/physio-geo.11977

Cited by 9 publications

(3 citation statements)

References 39 publications

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“…Moreover, further research is needed to understand at river basin scale the behaviour of underlying factors of hydrological changes during the last period. For this purpose, recent methodologies developed at small sub-basin or plot level [70,71] could be successfully integrated with large-scale remote sensing and spatial analysis approaches [23].…”

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confidence: 99%

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Massazza¹,

Bacci²,

Descroix³

et al. 2021

Water

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Niamey, the capital of Niger, is particularly prone to floods, since it is on the banks of the Niger River, which in its middle basin has two flood peaks: one in summer (the red flood) and one in winter (the black flood). In 2020, the Niger River in Niamey reached its all-time highest levels following an abundant rainy season. On the other hand, the floods in Niamey have been particularly frequent in the last decade, a symptom of a change in hydroclimatic behaviour already observed since the end of the great droughts of the 1970s and 1980s and which is identified with the name of Sahelian Paradox. This study, starting from the analysis of the 2020 flood and from the update of the rating curve of the Niamey hydrometric station, analyses the rainfall–runoff relationship on the Sahelian basins of the Medium Niger River Basin (MNRB) that are at the origin of the local flood. The comparative analysis of runoffs, annual maximum flows (AMAX) and runoff coefficients with various rainfall indices calculated on gridded datasets allowed to hydroclimatically characterise the last decade as a different period from the wet one before the drought, the dry one and the post-drought one. Compared to the last one, the current period is characterised by a sustained increase in hydrological indicators (AMAX +27%) consistent with the increase in both the accumulation of precipitation (+11%) and the number (+51%) and magnitude (+54%) of extreme events in the MNRB. Furthermore, a greater concentration of rainfall and extremes (+78%) in August contributes to reinforcing the red flood’s positive anomalies (+2.23 st.dev in 2020). The study indicates that under these conditions the frequency of extreme hydrological events in Niamey will tend to increase further also because of the concurrence of drivers such as river-bed silting and levee effects. Consequently, the study concludes with the need for a comprehensive flood-risk assessment on the Niamey city that considers both recent hydroclimatic trends and urbanisation dynamics in flood zones hence defining the most appropriate risk-reduction strategies.

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confidence: 99%

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Massazza¹,

Bacci²,

Descroix³

et al. 2021

Water

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“…1) Breakpoints detection analysis based on Pettitt's test Figure 7 and Table 5, Table 6 give the main breakpoints of the mean NDVI, precipitations and soil moisture data during the 1981-2020 period. Regarding the results of Table 5 and Table 6, According to [42], the spontaneous vegetation has undergone a strong regression in the Ferlo (Tessekere) region. [43] noted that the protected areas remained stable but there was a regression of the wooded and tree savannah areas.…”

Section: Analysis Of the Vegetation Cover Dynamic In The Senegalese G...mentioning

confidence: 95%

Recent Vegetation Cover Dynamics and Climatic Parameters Evolution Study in the Great Green Wall of Senegal

Gore¹,

Aman²,

Kouadio³

et al. 2023

JEP

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The drought recorded in 1970s and 1980s, particularly in the Sahara and Sahel region has greatly affected the population as well as the economies and the eco-systems of this area. In 2007, the African Union launched a Pan-African program, the Great Green Wall for the Sahara, the Sahel Initiative (GGWSSI) to reverse land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. The objective is to improve food security, and support local people to adapt to climate change. This paper aims to evaluate the impacts of the reforestation program in Senegal, fifteen years after it was launched. This study uses a time series of satellite-derived vegetation cover and climatic parameters data to analyze the sustainability of these interventions. Change detection approaches were applied to identify and characterize the drives of the eventual changes. A comparative analysis of reforestation on climatic parameters was explored through the temporal analysis of the vegetation index over the periods 2000-2008 and 2009-2020. An increase in vegetation activity was noted through the NDVI at the interannual (+2% to +8%) and seasonal (+1.5% to 7% for the wet season and 1% to 4% for the dry season) scale and a positive and significant evolution is noted on the trace of the GGW. Also, the period 2009-2020 recorded an increase in rainfall of 2% to 8% of the average value 2000-2020 and 4% to 8% of the rainy season. Soil moisture is the climatic parameter that has increased the most, with an increase of 25% to 54% of the 2000-2020 average, i.e. between 20 mm and 70 mm more.This study shows a significant improvement in the relationship between NDVI and climate parameters after the different reforestation actions of the GGW.

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“…A study based on 40 years satellite data carried out by the CILSS (Comité Inter-états de Lutte contre la Sécheresse dans le Sahel "CILSS" [9]) during 1975 and 2013 has shown that 26% of the land in Senegal are overexploited, included the agricultural areas causing savanna and open forest fragmentation. According to [15]), the spontaneous vegetation has been highly degraded (−13.4%) during 1974-2013 in the Ferlo region (Tessekere). [12] and [75] have shown that the losses in surface of protected areas are low for the steppe and high for the wooded and tree savanna.…”

Section: Analysis Of the Land Cover Dynamic In The Senegalese Great G...mentioning

confidence: 99%

Estimation of the Carbon Sequestration Dynamics of Senegal’s Great Green Wall Based on Land Cover over the Past Three Decades

Gore,

Aman,

Kouadio

et al. 2023

JEP

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The severe drought observed in the Sahel during 1970s, 1980s and 1990s has deeply affected the population as well as the economies and the eco-systems of this climatic area. The GGW Initiative spearheaded by Africa Union in 2007 proposed to combat the land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. A reforestation was then conducted in the Senegal's GGW since 2006 as part as other areas in the Sahel. This paper aims to evaluate the carbon sequestration dynamics in the sites of the Senegal's GGW over the last three decades. The method consists firstly of analyzing the evolution of land cover and land use dynamics based on ESA-CCI LC satellite data. There is an improvement of the surface areas of tree and shrub savanna of 11.40% (Tessekere), 8.25% (Syer) and 2.70% (Loughere-Thioly). The regreening of the different localities and a positive dynamic observed is explained by the return to normal rainfall and to reforestation actions, agroforestry practices, better management of natural resources undertaken. However, some non-reforested sites showed an opposite trend despite of the normal rainfall. Secondly, the results on land mapping are used as a proxy for the assessment of carbon stocks. The dynamic observed in vegetation cover since the beginning of the reforestation made it possible to sequester 5.8 million tons of carbon representing respectively 2.31% of African GGW. This gain in stored carbon is equivalent to 21.2 million tons of CO 2 captured in the atmosphere. Through this study, it appears that carbon storage becomes significant 8 to 10 years after the start of reforestation. An urbanization without respect for the environmental factors could be a danger for the climate (case of Ballou).

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Cartographie par télédétection des variations spatio-temporelles de la couverture végétale spontanée face à la variabilité pluviométrique au Sahel : approche multiscalaire

Cited by 9 publications

References 39 publications

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Recent Vegetation Cover Dynamics and Climatic Parameters Evolution Study in the Great Green Wall of Senegal

Estimation of the Carbon Sequestration Dynamics of Senegal’s Great Green Wall Based on Land Cover over the Past Three Decades

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