Fifty years of landscape evolution in Southwestern Mauritania by means of aerial photos

Abstract

South-western Mauritania is located in a semi-arid environment exposed to large rainfall variations and affected by a severe drought since the mid-1960s. The studied area includes the right bank of the Senegal River and the southern extension of the Saharan sandy dunes and is based on the analysis of climatic data, field studies, and four aerial surveys realized since 1954.The climatic analysis shows that, after a strong decline of yearly rainfall started in the mid-1960s, a significant increase is observed from the early 1990s. In the meantime, dust storms frequency has dramatically increased while the threshold wind speed declined as a result of vegetation contraction. The comparison of the four mosaics of aerial photos reveals the major impact of both drought and human on recent environment changes with the strong decline of the forest, the reactivation of sandy soils and the apparition of large rice fields.If the increase of active dunes activity is likely to be a consequence of the persisting drought, forest decline is more likely to be attributed to fuel wood collection in a first time, then to the creation of rice fields since the late 1980s. Although the 2003 aerial photos show a timid return of vegetation in very limited and specific areas, field surveys show that wind erosion is still very important and water erosion is developing very rapidly because of the absence of vegetation cover. r

Spatiotemporal Trend Analysis of the Mean Annual Rainfall in Senegal

“…These results may show sign towards a progressive return on more favorable rainfall conditions as mentioned by Ozer et al (2003). These results confirmed those of some authors (Ozer et al, 2003 ;Niang et al, 2008 ;Hountondji et al, 2009 ;Ozer et al, 2009 ;Ouoba, 2013 ;Panthou et al, 2014) who suggested a return of wetted period since the 1990s. However, they contrasted the findings of several other authors (L'hote et al, 2002 ;Frappart et al, 2009 ;Lebel et Ali, 2009).…”

Tree density and species decline in the African Sahel attributable to climate

“…On the other hand, research showed no decrease in tree density at sites in Burkina Faso (Rasmussen et al, 2001), Mali (Hiernaux et al, 2009), and the Republic of the Sudan (Schlesinger and Gramenopoulos, 1996). Agricultural expansion and livestock grazing, not climate, reduced tree density at sites in Mauritania (Niang et al, 2008) and Senegal (Lericollais, 1989). Recent natural regeneration by farmers increased tree density at a site in Burkina Faso (Reij et al, 2005).…”

How hazardous is the Sahara Desert crossing for migratory birds? Indications from satellite tracking of raptors

“…The harshness of the desert, low probability of finding prey and high risk of dehydration certainly affect survival of migrating birds. This is aggravated by strong winds, creating dust storms which have dramatically increased in frequency since the late 1950s (Goudie & Middleton 2006;Niang et al 2008). In order to investigate possible difficulties and hazards for avian migrants crossing this geographical barrier, we have evaluated migratory journeys across the Sahara Desert made by raptors recorded by satellite telemetry.…”