• Energy Research

AbstractIn this paper, we study the impact of climate change on river regimes in several parts of Africa, and we look at the most probable causes of these changes either climatically or anthropogenically driven. We study time series of updated monthly and annual runoff of rivers of North Africa, West Africa (Sahelian and humid tropical regions) and Central Africa, including the largest river basins: Niger and Volta rivers in West Africa, and Congo and Ogooue rivers in Central Africa. The recent years are studied in the perspective of multi‐decadal variability. In West Africa and in a part of Central Africa, the climate has changed since 1970, and rainfall has not returned to previous annual amounts, except in Equatorial Africa. The consequences of the long‐lasting drought are, depending on the area concerned, the modification of seasonal regimes (Equatorial area), the groundwater table decrease (Tropical humid area) and the land cover degradation (Sahelian area). The increasing number of dams and of agricultural areas also plays a major role on the modification of river regimes. The population increase will continue to impact on the environment: land cover change, deforestation, agriculture and increasing number of dams will be associated with a reduction of water and sediment discharges to the sea, and major impacts on downstream ecosystems and coastal areas. It seems necessary to share with stakeholders a comprehensive approach of the water cycle from the basin to the sea, to prevent long‐lasting damages to ecosystems and infrastructures. Copyright © 2013 John Wiley & Sons, Ltd.

Many studies have been undertaken on climate variability in West Africa since the drastic drought of 1970s. These studies rely in many cases on different baseline periods chosen with regard to the reference periods defined by the World Meteorological Organization. A method is developed in this study to determine a stationary baseline period for rainfall variability analysis. The method is based on an application of three statistic tests (on deviation and trend) and a test of shifts detection in rainfall time series. The application of this method on six different gridded rainfall data and observations from 1901 to 2018 shows that the 1917–1946 period is the longest stationary period. An assessment of the significance of the difference between the mean annual rainfall amount during this baseline period and the annual rainfall amount during the other years shows that the “Normal” annual rainfall amount is defined by an interval delineated by ±the standard deviation (STD). With regard to this interval, a very wet/dry year is defined with a surplus/gap over/below the STD. Overall the 1901–2018 period, the 1950–1970 period presents the most important number of significant wet years and the 1971–1990 period presents the most important number of significant dry years.

International audience

Abstract The problem of using data outputs from general circulation models (GCMs) to assess the impacts of climate change on runoff in West Africa is addressed. The annual and monthly precipitation data from four GCMs used in the Third Assessment Report of the IPCC were studied over the 1950–1998 period: the CSIRO-Mk2, ECHAM4, HadCM3 and NCAR-PCM models. Two weaknesses common to all these models are their inability to reproduce rainfall volumes in the Sahelian zone, and their difficulty in simulating the seasonal dynamics of rainfall in the Guinean zone. Two climate scenarios were then developed based on the changes predicted by the HadCM3-A2 model, which aimed to generate time series for rainfall and potential evapotranspiration up to the end of the 21st century, in order to simulate probable future climatic conditions. These scenarios were used as input to the hydrological model GR2M to assess the impacts of climate change on the discharge of four main rivers: the Senegal, the Gambia, the Sassandra and ...

The Paris Climate Agreements and Sustainable Development Goals, signed by 197 countries, present agendas and address key issues for implementing multi-scale responses for sustainable development under climate change—an effort that must involve local, regional, national, and supra-national stakeholders. In that regard, Continental Carbon Sequestration (CoCS) and conservation of carbon sinks are recognized increasingly as having potentially important roles in mitigating climate change and adapting to it. Making that potential a reality will require indicators of success for various stakeholders from multidisciplinary backgrounds, plus promotion of long-term implementation of strategic action towards civil society (e.g., law and policy makers, economists, and farmers). To help meet those challenges, this discussion paper summarizes the state of the art and uncertainties regarding CoCS, taking an interdisciplinary, holistic approach toward understanding these complex issues. The first part of the paper discusses the carbon cycle’s bio-geophysical processes, while the second introduces the plurality of geographical scales to be addressed when dealing with landscape management for CoCS. The third part addresses systemic viability, vulnerability, and resilience in CoCS practices, before concluding with the need to develop inter-disciplinarity in sustainable science, participative research, and the societal implications of sustainable CoCS actions.

L'objectif de cet article est d'étudier le changement climatique dans le bassin versant de l'Ogooué : évolution récente et impact sur les écoulements. Pour cela, les données hydropluviométriques de ce bassin ont été analysées au moyen du test de Pettitt. Les résultats de cette étude révèlent une diminution statistiquement significative des modules annuels que le test de Pettitt situe en 1972-73, mais rien de tel pour les pluies à ce même pas de temps. Les écarts des moyennes décennales à la moyenne interannuelle montrent cependant des liens plus nets entre ces variables, se traduisant essentiellement par une diminution synchrone au cours des décennies 1970 et 1980. Cette diminution est suivie d'une reprise au cours des deux décennies d'après (1990 et 2000), laquelle s'estompe à nouveau au cours de la décennie 2010. Les écoulements des saisons pluvieuses (printemps et automne) ont enregistré les modifications les plus importantes, suite aux variations des régimes pluviométriques des saisons sèches (hiver et été) qui les précèdent. La saison sèche d'hiver a connu entre les décennies 1970-1990 une diminution importante des précipitations qui a provoqué une chute des écoulements du printemps. Le rehaussement et la flexion respectivement notés au cours des décennies 2000 et 2010 s'accompagnent des mêmes tendances dans les écoulements du printemps. A l'inverse, entre les décennies 1980-1990, il a été noté une hausse conjointe des pluies d'été et des écoulements d'automne. La flexion des pluies d'été observée depuis la décennie 2000 est également perceptible dans les écoulements d'automne. Ces résultats pourraient servir à renforcer les capacités de gestion des ressources en eau dans le bassin versant concerné et dans la région. Ils apportent également de nouveaux éléments pour étudier et comprendre la variation saisonnière et la disponibilité de l'eau douce en aval, dans les estuaires et les zones côtières des rivières régionales. The objective of this article is to study climate change in the Ogooue watershed: recent evolution and impact on flows. For this, the hydropluviometric data of this basin were analyzed using the Pettitt test. The results of this study reveal a statistically significantdecrease in runoff that the Pettitt test situates in 1972-73, but nothing like that for rainfallat this same time scale. The decadal deviations from the inter-annual average, however, show clearer links between these variables, resulting mainly in a synchronous decrease during the 1970s and 1980s. This decrease is followed byanincreaseduring the 1990s and 2000s, which diminished again during the 2010s. The flows of the rainy seasons (spring and autumn) recorded the most significant modifications, following variations in the rainfall patterns of the dry seasons (winter and summer) that precede them. The winter dry season recorded a significant decrease in rainfall between the decades 1970 and 1990, which caused a drop in spring flows. The increasingand decreasing respectively noted during the 2000s and 2010s are accompanied by the same trends in the spring flows. Conversely, between the decades 1980 and1990,there was a joint increase in summer rainfall and autumn flows. The decrease in summer rainfall observed since the 2000s is also noticeable in the autumn flows. These results could be used to strengthen water resources management capacities in the watershed concerned and the region. They also provide new insights to study and understand seasonal variation and availability of freshwater downstream, in estuaries and coastal areas of regional rivers.