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1. Estimating groundwater resources in an equatorial forested basin using geographic information system and remote sensing techniques (case of Nyong, South Cameroon)

Author

Valentin Brice Ebode and Bernadette Nka Nnomo

Subjects
analytical hierarchy process, equatorial area, geographic information system, nyong basin, remote sensing, Water supply for domestic and industrial purposes, TD201-500, River, lake, and water-supply engineering (General), TC401-506
Abstract

This article aims to produce a groundwater potential zone (GWPZ) map of the Nyong basin using an integrated analytical hierarchy process driven in a geographic information system (GIS) environment. For this, seven parameters (rainfall, geology, slopes, drainage density, land use and land cover, lineament density, and soil) known to influence the availability of groundwater were considered. The results obtained show that the Eastern part of the basin holds the largest quantities of groundwater. The produced map shows that this region includes high and very high GWPZs (yield > 6 l/s). It is essentially characterized by abundant rainfall (on average 135–136 and 131–134 mm), low slopes, significant drainage and lineament densities, and significant forest cover. On the other hand, the opposite region (west), which includes the low and very low GWPZs, is characterized by less abundant precipitation (on average 121–125 and 125–128 mm), significant slopes, lower drainage and lineament densities, and greater impervious areas. With a success rate of 80%, confidence deserves to be placed in the GWPZs map produced. It can be considered in water supply projects in this basin. Such work has never been done in this basin before. HIGHLIGHTS Groundwater potential zones in equatorial are addressed using the analytical hierarchy process.; Rainfall forecast in the equatorial area is addressed.; The model for which rainfall seems the most reliable is addressed.;

Published
2024
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2. Design models for small run-of-river hydropower plants: a review

Author

David Tsuanyo, Boris Amougou, Abdoul Aziz, Bernadette Nka Nnomo, Davide Fioriti, and Joseph Kenfack

Subjects
Run-of-river, Hydropower plant, Optimal design, Energy system modeling, Mini-grids, Renewable energy sources, TJ807-830
Abstract

Highlights A critical review focused particularly on run-of-river hydropower plant design models was carried out. Several calculation models including diameter and thickness of a penstock, admissible suction head of a turbine, and cost and energy production estimation for grid-connected applications are collected and analyzed. Hydropower models for design and generation profile prediction presented can be used to optimally come against the variability problem of run-of river plants. The paper can be used as a guide in the design and simulation of run-of-river hydropower plants with appropriate models.

Published
2023
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3. Effects of climate and anthropogenic changes on current and future variability in flows in the So'o River Basin (south of Cameroon)

Author

Valentin Brice Ebodé, Jean Guy Dzana, Elias Nkiaka, Bernadette Nka Nnomo, Jean Jacques Braun, and Jean Riotte

Subjects
change in land use modes, climate change, current discharges, future discharges, regional climate models, southern cameroon, River, lake, and water-supply engineering (General), TC401-506, Physical geography, GB3-5030
Abstract

Due to climate and environmental changes, sub-Saharan Africa (SSA) has experienced several drought and flood events in recent decades with serious consequences on the economy of the sub-region. In this context, the region needs to enhance its capacity in water resources management, based on both good knowledge of contemporary variations in river flows and reliable forecasts. The objective of this article was to study the evolution of current and future (near (2022–2060) and distant (2061–2100)) flows in the So'o River Basin (SRB) in Cameroon. To achieve this, the Pettitt and modified Mann–Kendall tests were used to analyze hydrometeorological time series in the basin. The Soil and Water Assessment Tool (SWAT) model was used to simulate the future flows in the SRB. The results obtained show that for the current period, the flows of the So'o decrease due to the decrease in precipitation. For future periods, a change in precipitation in line with the predictions of the CCCma model will lead to a decrease in river discharge in the basin, except under the RCP8.5 scenario during the second period (2061–2100), where we note an increase compared to the historical period of approximately +4%. Results from the RCA4 model project an increase in precipitation which will lead to an increase in river discharge by more than +50%, regardless of the period and the scenario considered. An increase in discharges was noted in some cases despite a drop in rainfall, particularly in the case of discharges simulated for the second period (2061–2100) from the outputs of the CCCma model. This seems to be a consequence of the increase in impervious spaces, all the more the runoff increases during this period according to the model. Results from this study could be used to enhance water resources management in the basin investigated and the region. HIGHLIGHTS Impact of current climate change and anthropization on river discharge in equatorial central Africa.; Impact of future climate change and anthropization on river discharge in equatorial central Africa.;

Published
2022
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4. Impact of future climate change and anthropization on the discharges of the So'o watershed (South Cameroon)

Author

Valentin Brice Ebodé, Gil Mahé, Jean-jacques Braun, Jean-guy Dzana, Jules Remy Ndam Ngoupayou, and Bernadette Nka Nnomo

Abstract

The purpose of this article is to get an idea of ​​the evolution of the flows of the So’o basin in the relatively near future (2022-2060), but also in the distant future (2061-2100). In this perspective, the Cellular Automata (CA) -Markov was used to predict the evolution of the future land use of the basin, and the outputs of three regional climate models/RCMs (RCA4, RACMO22T and CCCma) were used to predict future climate change. Distribution mapping was retained as a method of correcting the precipitation and temperature biases of the outputs of the climate models used. The SWAT (Soil and Water Assessment Tool) model was used to simulate the future flows of the So’o. The results obtained show that a change in precipitation in accordance with the forecasts of the CCCma and RACMO22T models will be the cause of a decrease in the runoff, except under the RCP8.5 scenario during the second period (2061-2100), where we will note an increase compared to the historical period of approximately + 4%. This decrease will mainly affect the months of autumn, and the decades 2020, 2040 and 2070 will be the most affected. Concerning the RCA4 model, the results obtained show that a change in precipitation following its forecasts will cause an increase in runoff of more than 50%, regardless of the period and the scenario taken into account. In general, this increase will be greatest during the dry seasons (winter and summer), and the decades at the end of the century (2080s to 2100s) will be the wettest. An increase in discharges was noted in certain cases despite a decrease in rainfall, in particular in the case of flows simulated for the first period (2022-2060) from the outputs of the CCCma model. This seems to be a consequence of the increase in impervious areas, insofar as the runoff also increases during this period according to the model. The results of this study could be used to strengthen the management of future water resources in the basin and the entire region.Keywords: So’o, RCMs, Climate Change, Anthropization, SWAT

Published
2022
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5. Flows variability in a forest watershed undergoing accelerated urbanization: the case of Mefou (South Cameroon)

Author

Valentin Brice Ebodé, Gil Mahé, Jean-jacques Braun, Jean-guy Dzana, Jules Remy Ndam Ngoupayou, and Bernadette Nka Nnomo

Abstract

The objective of this study is to understand the impact of rainfall variability and anthropization on the flows of the Mefou watershed over a recent period. For this, the hydropluviometric data of the catchment concerned were analyzed using the Pettitt test. Likewise, the dynamics of the main land-use patterns have been assessed, using supervised classifications carried out from the processing of Landsat satellite images of the basin studied at two dates. The results of this study show that the average and extreme flows of this basin have been increased since 1985-86, unlike the rainfall, which generally decreases for all seasons from the 1970s, apart from the summer, where the reverse is observed. Land-use changes (increase in impervious areas and a decrease in forest and water bodies) seem to be the main cause of the observed increase in runoff. The rainfall changes observed in this basin have just contributed to amplifying this increase in runoff in some cases and attenuating it in others. The summer and the spring for which the rainfall recorded respectively an increasing break and no break are also the seasons for which the increases in runoff are the most important. Conversely, autumn and winter, which saw significant decreases in rainfall, experienced the smallest increases. These results could be useful for long-term planning of water demand and use in this basin, as well as for improving future simulations of main collector flow and preventing socio-environmental disasters like flooding.Keywords: Mefou, variability, precipitation, runoff, land use patterns

Published
2022
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6. The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset I: The Nyong River Basin, Cameroon

Author

Jean-Pierre Bedimo Bedimo, Mikael Faucheux, Olivier Ribolzi, Jean-Christophe Maréchal, Bernadette Nka Nnomo, Justin Nlozoa, Bernard Dupré, Christelle Lagane, Jules Remy Ndam-Ngoupayou, Jean Riotte, Jean-Claude Ntonga, Jean-Jacques Braun, Emma Rochelle-Newall, L. Ruiz, Laurie Boithias, Jean-Loup Boeglin, Stéphane Audry, Henriette Ateba Bessa, Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Institut de Recherche pour le Développement (IRD), Sol Agro et hydrosystème Spatialisation (SAS), AGROCAMPUS OUEST, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Gestion de l'Eau, Acteurs, Usages (UMR G-EAU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), University of Yaoundé [Cameroun], Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), International Joint Laboratory DYCOFAC, Institut de Recherches Géologiques et Minières (IRGM), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-INSTITUT AGRO Agrocampus Ouest, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)

Subjects
010506 paleontology, Watershed, [SDV]Life Sciences [q-bio], Drainage basin, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Weathering, 010502 geochemistry & geophysics, 01 natural sciences, hydrochemistry, Streamflow, Tributary, Cameroon, humid tropics, 0105 earth and related environmental sciences, Water Science and Technology, 2. Zero hunger, Hydrology, geography, geography.geographical_feature_category, Tropics, ZONE TROPICALE HUMIDE, CZO, 15. Life on land, Critical Zone Observatories, monitoring, 13. Climate action, weathering, Erosion, Environmental science, CAMEROUN
Abstract

International audience; Simultaneously acquiring time series of climate, hydrology and hydrochemical data over decades on river systems is pivotal to understand the complex interactions involving rock, soil water, air and biota in the Critical Zone, to build integrated modelling and to propose predictive scenarios. Among the Critical Zone Observatories (CZOs) implemented in the past 25 years, only a few are located in the humid Tropics despite the importance of these regions in terms of population density, fast-changing land use, biodiversity hotspots, biomass stock on continents, size of river systems, etc. Since 1994, weathering and erosion processes and fluxes have been investigated at both local (experimental watershed) and regional scales in the Nyong River Basin (Cameroon) which belongs to the Critical Zone Observatories network named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Cameroon are: (1) rainfall; (2) air temperature, air relative humidity, wind speed and direction, and global radiation; (3) stream and river water level; (4) pH, electrical conductivity, water temperature and suspended particulate matter (SPM) concentration; (5) major ion, alkalinity and dissolved organic carbon (DOC) concentrations. The dataset already contributed to describe the water partitioning in these tropical humid watersheds, to better understand the factors controlling chemical weathering and physical erosion in tropical ecosystems, particularly the role of organic matter. The dataset also contributed to calculate elemental weathering fluxes and saprolite production rate and to propose denudation rates on tropical cratonic landscapes. Hydrological modelling allowed quantification of the geographical water sources contributing to streamflow. DOC data were used to determine greenhouse-gas emissions and carbon budgets from African inland waters. However, long-term solute concentrations at the outlet of a small tributary of the Nyong River exhibit non-stationary behaviour over the last 26 years. The processes governing those fluctuations are not yet fully understood and might be related to changes in the hydrological regime, land-cover and land-use. The latter highlights the need for longer time-series and continued support for CZOs particularly in the humid tropics.

Published
2021
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7. Are the Fouta Djallon Highlands Still the Water Tower of West Africa?

Author

Julien Andrieu, Yves Boulvert, Jean-Louis Couture, Bachir Tanimoun, Luc Ferry, Gwenaelle Dejacquelot, Aliou Barry, Luc Descroix, Fatoumata Binta Sombily Diallo, Ange Bouramanding Diedhiou, Jean-Pierre Vandervaere, Ababacar Fall, Lamine Konaté, Mahamadou Diakité, Bernadette Nka Nnomo, Amirou Diallo, Safietou Soumaré, Eugenia Gallese, Honoré Dacosta, Yaya Sakho, Kadiatou Diallo, Sylvie Paméla Manga, Ansoumana Bodian, Jean Albergel, Gil Mahé, Kourahoye Diallo, Jean-Claude Bader, Didier Orange, Bakary Faty, Jean-Claude Olivry, Nadine Braquet, Andrew Ogilvie, Laurent Lambert, Ilia Amadou, Saly Sambou, Patrimoines locaux, Environnement et Globalisation (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU), Patrimoines et Territoires de l'eau (LMI PATEO), Patrimoines Locaux et Gouvernance (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Direction de la Gestion et la Planification des Ressources en Eau (DGPRE), Université Assane SECK de Ziguinchor (UASZ), Université de Lorraine (UL), Université Félix Houphouët-Boigny (UFHB), School of Public Administration and Development Economics, Doha Institute for Graduate Studies, Ecole polytechnique de Thiès, Ecole Polytechnique de Thiès, Études des Structures, des Processus d’Adaptation et des Changements de l’Espace (ESPACE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Université Côte d'Azur (UCA), Université Côte d'Azur (UCA), Gestion de l'Eau, Acteurs, Usages (UMR G-EAU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Centre de recherche pluridisciplinaire en Lettres, Langues, Sciences Humaines et des Sociétés (Pléiade), Université Paris 13 (UP13), Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université Gamal Abdel Nasser de Conakry, Institut Universitaire des Hautes Etudes de Guinée (IUHEG), Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, NBA Niger Basin Authority, Direction Nationale de l'Hydraulique [Guinée], Girardel - Laboratoire Leïdi (Leïdi), Université Gaston Berger de Saint-Louis Sénégal (UGB), Institut de Recherche pour le Développement (IRD), Independent Consultant, Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Grdr Migrations, Citoyenneté, Développement, Organisation Pour la Mise en Valeur du Bassin du Fleuve Sénégal (OMVS), Institut de Recherches Géologiques et Minières (IRGM), Organisation pour la Mise en Valeur du Bassin du Fleuve Gambie (OMVG), Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes (UMR Eco&Sols), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Service National des Sols (SENASOLS), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), European Union, via AICS (Agenzia Italiana de Cooperazione per il Sviluppo) ENV/2017/383-744/AP n, Sorbonne Université (SU)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Université Côte d'Azur (UCA)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), and Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )

Subjects
Fula society, lcsh:Hydraulic engineering, depletion (or recession) coefficient, 010504 meteorology & atmospheric sciences, Geography, Planning and Development, 0207 environmental engineering, 02 engineering and technology, Aquatic Science, 01 natural sciences, Biochemistry, Natural (archaeology), West africa, Vegetation cover, lcsh:Water supply for domestic and industrial purposes, lcsh:TC1-978, basement, sandstone, runoff coefficient, 020701 environmental engineering, soil water holding capacity, 0105 earth and related environmental sciences, Water Science and Technology, lcsh:TD201-500, geography, Plateau, geography.geographical_feature_category, Fouta Djallon, 15. Life on land, 6. Clean water, Basement (geology), 13. Climate action, Threatened species, [SDE]Environmental Sciences, Physical geography, Surface runoff, Tower, water tower
Abstract

A large share of surface water resources in Sahelian countries originates from Guinea&rsquo, s Fouta Djallon highlands, earning the area the name of &ldquo, the water tower of West Africa&rdquo, This paper aims to investigate the recent dynamics of the Fouta Djallon&rsquo, s hydrological functioning. The evolution of the runoff and depletion coefficients are analyzed as well as their correlations with the rainfall and vegetation cover. The latter is described at three different space scales and with different methods. Twenty-five years after the end of the 1968&ndash, 1993 major drought, annual discharges continue to slowly increase, nearly reaching a long-term average, as natural reservoirs which emptied to sustain streamflows during the drought have been replenishing since the 1990s, explaining the slow increase in discharges. However, another important trend has been detected since the beginning of the drought, i.e., the increase in the depletion coefficient of most of the Fouta Djallon upper basins, as a consequence of the reduction in the soil water-holding capacity. After confirming the pertinence and significance of this increase and subsequent decrease in the depletion coefficient, this paper identifies the factors possibly linked with the basins&rsquo, storage capacity trends. The densely populated areas of the summit plateau are also shown to be the ones where vegetation cover is not threatened and where ecological intensification of rural activities is ancient.

Published
2020
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8. Impact of Rainfall Variability and Land Use Change on River Discharge in South Cameroon

Author

Valentin Brice Ebodé, Jean Jacques Braun, Bernadette Nka Nnomo, Gil Mahé, Elias Nkiaka, and Jean Riotte

Subjects
Geography, Planning and Development, forcings, precipitation, runoff, land use, Nyong, Central Africa, Aquatic Science, Biochemistry, Water Science and Technology
Abstract

Climate change, variability and anthropogenic forcings such as land use change are the main forcings of river discharge variability. However, an understanding of their simultaneous impacts on river discharge remains limited in some parts of the world. To shed light on this issue, the objective of this article is to investigate the effects of rainfall variability and land use change on river discharge in the Nyong basin (at Olama and Mbalmayo gauging stations) and some of its sub-basins (So’o and Mefou) over the long period 1950–2018. To achieve this goal, hydro-meteorological data of the Nyong basin and sub-basins were analyzed using the Pettitt test. Likewise, land use changes in the basin and sub-basins were also analyzed using supervised classifications of Landsat satellite images of the basins at different periods (1973, 2000 and 2018). On the annual scale, rainfall has decreased statistically over the studied basins. In the large basins (Olama and Mbalmayo), this decrease in rainfall is synchronous with that of discharges, while it is concomitant with an increase in the Mefou (small basin). After the ruptures within time series identified in the annual modules, the extreme discharges (maximum and minimum) decreased in Olama; in Mbalmayo, the maximum discharges remained stable while the minimum discharges decreased. On the other hand, the maximum and minimum discharges have significantly increased in the Mefou. The stability of maximum discharges at Mbalmayo and the increase in extremes on the Mefou in a context where the precipitation that generates the discharge has decreased can be attributed to land use change. These changes are essentially marked by an increase in impervious areas and a reduction in forest cover. On the seasonal scale, the impact of precipitation in the dry season is visible on the flows of the rainy seasons that follow them on the large basins (Olama and Mbalmayo). Between the decades 1970–1990 and 2000–2010, there was respectively a significant increase, then a decrease in summer precipitation, which impacted the autumn discharges in the same direction. Conversely, between the same intervals, there was a significant decrease, then a slight increase in winter precipitation. The impact of winter precipitation on the spring discharge is more visible during the first period only (1970–1990). During the second period, winter precipitation seems to have more of an impact on the runoff for the same season. In the Mefou sub-basin, the precipitation plays an essentially amplifying role in the increase in discharge in the seasons during which they occur. Those having experienced an increase, or a maintenance of precipitation (summer and spring) recorded the most significant increases in discharges. These results could be useful for long-term planning on the demand and use of water, as well as flood management in the basins

Published
2022
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