Anthropization and Climate Change: Impact on the Discharges of Forest Watersheds in Central Africa

Abstract

Climate change and anthropization are major drivers of river flows variability. However, understanding their simultaneous impact on discharges is limited. As a contribution to address this limitation, the objective of this study is to assess the impact of climate change and anthropization on the discharges of two watersheds of Central Africa (Nyong and Ntem) over a recent period. For this, the hydropluviometric data of the watersheds concerned were analyzed using the Pettitt test. Similarly, the dynamics of the main land use modes (LUM) have been assessed, through classifications obtained from the processing of Landsat satellite images of the watersheds studied on two dates. The results of this study show that in Central Africa, annual discharges have decreased significantly since the 1970s, and yet the decline in annual rainfall does not become significant until the 2000s. The discharges of the rainy seasons (spring and autumn) recorded the most important changes, following variations in the rainfall patterns of the dry seasons (winter and summer) that precede them. Winters experienced a significant decrease in precipitation between the 1970s and 1990s, which caused a drop in spring flows. Their rise, which began in the 2000s, is also accompanied by an increase in spring flows, which nevertheless seems rather slight in the case of the Nyong. Conversely, between the 1970s and 1990s, there was a joint increase in summer rainfall and autumn flows. A decrease of summer rainfall was noted since the 2000s, and is also noticeable in autumn flows. Maximum flows have remained constant on the Nyong despite the slight drop in rainfall. This seems to be the consequence of changes in land use patterns (diminution of forest and increasing of impervious areas). The decrease in maximums flows noted on the Ntem could be linked to the slight drop in precipitation during the rainy seasons that generates it. Factors such as the general decrease in precipitation during the winter and the reduction in the area occupied by water bodies could justify the decrease in minimum flows observed in the two watersheds. These findings would be vital to enhance water management capabilities in the watersheds concerned and in the region. They can also give some new elements to study and understand the seasonal variation and fresh water availability in downstream, estuaries and coastal areas of the regional rivers.

Impact de la variabilité climatique et de l'anthropisation sur les écoulements de la Bénoué (nord Cameroun)

“…Ces formations imperméables agissent dans le sens d'un accroissement du ruissellement et, par conséquent, des écoulements. Des études effectuées ailleurs sont parvenus à des résultats similaires (Aulenbach et al, 2017 ;Ebodé et al, 2020a). Il est aussi tout à fait possible de s'interroger sur les causes de l'augmentation récente des écoulements observée sur le bassin de la Bénoué, et en particulier sur son absence durant la saison humide et dans les maxima.…”

“…L'effet du déficit pluviométrique sur les ressources en eau de surface a été mis en évidence par de nombreuses études en milieu tropical africain (Paturel et al, 2003 ;Liénou et al, 2008 ;Sidibé et al, 2018Sidibé et al, , 2020Tramblay et al, 2020 ;Ebodé, 2020 ;Ebodé et al, 2020a). Les changements climatiques observés au cours des cinquante dernières années dans cette région, notamment au nord Cameroun, induisent des impacts visibles dans le cycle hydrologique du bassin versant de la Bénoué (Fita, 2020).…”

“…Par exemple, la construction du barrage de Lagdo entre 1977 et 1982, et sa mise en service depuis 1983, pourrait avoir entraîné une modification du régime hydrologique de la Bénoué. Il en est de même de l'accroissement de la population observé dans le bassin (BUCREP, 2011), qui a pour corollaire l'accroissement des surfaces imperméabilisées dont le rôle sur les écoulements a largement été prouvé ailleurs (Aulenbach et al, 2017 ;Diem et al, 2017 ;Ebodé et al, 2020a).…”

Special Issue “Multiscale Impacts of Anthropogenic and Climate Changes on Tropical and Mediterranean Hydrology”

“…The topics studied cover a large panel of hydrological questions. Many of them deal with the study of time series variability, rainfall [16], discharges [19,20], sediment transport [11][12][13]21], recession coefficient [22,23], climate change impacts [17,24], or anthropogenic impacts [2,11,20,21]. Drought is also a topic of notable interest in Mediterranean and tropical areas [23][24][25].…”

“…In several studies, authors search for the possible origin, climatic or anthropogenic, of the interannual variability observed in the times series of rainfall and discharges. In Central Africa, Ebodé et al [20] study the impact of anthropization and climate change on two forested watersheds (of Ntem and Nyong) in the south of the country, under equatorial and sub-equatorial climates. The results of this study show that in Central Africa, annual discharges have decreased significantly since the 1970s, and yet the decline in annual rainfall does not become significant until the 2000s.…”