[ Etude d’impact prospective des débits de crues dans un contexte de changements climatiques en Afrique de l’Ouest: Cas du bassin versant du N’zo (Sassandra, Ouest de la Côte d’Ivoire) ]
Volume 57, Issue 2, November 2021, Pages 117–131
Amani Michel Kouassi1, Gnangouin Asaph Yahot Joel2, Yao Charles Armel3, and N’Guessan N’Guessan Emilienne4
1 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), Département des Sciences de la Terre et des Ressources Minières (STeRMi), Laboratoire du Génie Civil, des Géosciences et des Sciences Géographiques, BP 1093 Yamoussoukro, Côte d'Ivoire
2 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Doctorale Polytechnique (EDP), B.P. 1093, Yamoussoukro, Côte d’Ivoire
3 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Supérieure des Mines et de Géologie (ESMG), B.P. 1093, Yamoussoukro, Côte d’Ivoire
4 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Supérieure des Mines et de Géologie (ESMG), B.P. 1093, Yamoussoukro, Côte d’Ivoire
Original language: French
Copyright © 2021 ISSR Journals. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The study area is the N'zo-Sassandra (West of Ivory Coast) watershed which is located between longitudes 7°15' and 8°05' West and latitudes 6°50' and 7°50' North. Its area is estimated at 4,310 km2. The objective of this study is to analyze the forecast of the flood flows of the N’zo (Sassandra) river located in the west of the Ivory Coast. The hydroclimatic data used (rainfall, ETP, flow) within the framework of this study extend on the one hand over the historical period (1961-2017) and on the other hand over the future period (2036-2065). The methodological approach adopted is based respectively on the analysis of past floods, the evaluation of the chosen rainfall-discharge model, the prospective climatic analysis and the prospective analysis of the flood flows. The variables used to describe the future evolution of these floods are the decennial and centennial quantiles of the annual maximum monthly mean discharges. Thus, an optimistic climate forecast scenario was used (RCP 2.6). This climatic scenario then fed into a hydrological rainfall-discharge model (GR2M model) calibrated to the reference period 1961-1990 and validated over the period 1991-2017. In response to climate forcing, future monthly flood discharges (QMXA) were simulated. The main results show that the best statistical law retained following the frequency analysis of the flood flows is the Gamma law which was used to estimate the frequency flows. The GR2M model evaluated, presented a good performance in calibration (79.7%) as in validation (82.7%) and demonstrated a great robustness (+3%) therefore a great capacity to reconstitute the flows of N'zo in Kahin. The climate forecast has shown a decrease in precipitation (-19.7%) and an increase in temperature (+1.6 °C) in the middle of the current century (2036-2065). The expected flood flow quantiles in the middle of the 21st century (2035-2065) are respectively 168.85 m3/s for the ten-year flow and 299.58 m3/s for the one-year flow. Thus, in response to climate change, the forecast of flood flows leads to a worrying drop in frequency flood flows, respectively of the order of 64.56% for the ten-year flood and 61.73% for the 100-year flood compared to their current values.
Author Keywords: Climate change, Hydrological forecasting, Flood flows, GR2M model, N’zo-Sassandra, Ivory Coast.
Volume 57, Issue 2, November 2021, Pages 117–131
Amani Michel Kouassi1, Gnangouin Asaph Yahot Joel2, Yao Charles Armel3, and N’Guessan N’Guessan Emilienne4
1 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), Département des Sciences de la Terre et des Ressources Minières (STeRMi), Laboratoire du Génie Civil, des Géosciences et des Sciences Géographiques, BP 1093 Yamoussoukro, Côte d'Ivoire
2 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Doctorale Polytechnique (EDP), B.P. 1093, Yamoussoukro, Côte d’Ivoire
3 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Supérieure des Mines et de Géologie (ESMG), B.P. 1093, Yamoussoukro, Côte d’Ivoire
4 Institut National Polytechnique Félix Houphouët-Boigny (INP-HB), École Supérieure des Mines et de Géologie (ESMG), B.P. 1093, Yamoussoukro, Côte d’Ivoire
Original language: French
Copyright © 2021 ISSR Journals. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
The study area is the N'zo-Sassandra (West of Ivory Coast) watershed which is located between longitudes 7°15' and 8°05' West and latitudes 6°50' and 7°50' North. Its area is estimated at 4,310 km2. The objective of this study is to analyze the forecast of the flood flows of the N’zo (Sassandra) river located in the west of the Ivory Coast. The hydroclimatic data used (rainfall, ETP, flow) within the framework of this study extend on the one hand over the historical period (1961-2017) and on the other hand over the future period (2036-2065). The methodological approach adopted is based respectively on the analysis of past floods, the evaluation of the chosen rainfall-discharge model, the prospective climatic analysis and the prospective analysis of the flood flows. The variables used to describe the future evolution of these floods are the decennial and centennial quantiles of the annual maximum monthly mean discharges. Thus, an optimistic climate forecast scenario was used (RCP 2.6). This climatic scenario then fed into a hydrological rainfall-discharge model (GR2M model) calibrated to the reference period 1961-1990 and validated over the period 1991-2017. In response to climate forcing, future monthly flood discharges (QMXA) were simulated. The main results show that the best statistical law retained following the frequency analysis of the flood flows is the Gamma law which was used to estimate the frequency flows. The GR2M model evaluated, presented a good performance in calibration (79.7%) as in validation (82.7%) and demonstrated a great robustness (+3%) therefore a great capacity to reconstitute the flows of N'zo in Kahin. The climate forecast has shown a decrease in precipitation (-19.7%) and an increase in temperature (+1.6 °C) in the middle of the current century (2036-2065). The expected flood flow quantiles in the middle of the 21st century (2035-2065) are respectively 168.85 m3/s for the ten-year flow and 299.58 m3/s for the one-year flow. Thus, in response to climate change, the forecast of flood flows leads to a worrying drop in frequency flood flows, respectively of the order of 64.56% for the ten-year flood and 61.73% for the 100-year flood compared to their current values.
Author Keywords: Climate change, Hydrological forecasting, Flood flows, GR2M model, N’zo-Sassandra, Ivory Coast.
Abstract: (french)
La zone d’étude est le bassin versant du N’zo-Sassandra (Ouest de la Côte d’Ivoire) qui se situe entre les longitudes 7° 15’ et 8° 05’ Ouest et les latitudes 6° 50’ et 7° 50’ Nord. Sa superficie est estimée à 4 310 Km2. Cette étude a pour objectif d’analyser la prospective des débits de crue du fleuve N’zo (Sassandra) situé à l’Ouest de la Côte d’Ivoire. Les données hydroclimatiques utilisées (pluie, ETP, débit) dans le cadre de cette étude s’étendent d’une part sur la période historique (1961-2017) et d’autre part sur la période future (2036-2065). La démarche méthodologique adoptée est basée respectivement sur l’analyse des crues passées, l’évaluation du modèle pluie-débit choisi, l’analyse prospective climatique et l’analyse prospective des débits de crue. Les variables retenues pour décrire l’évolution future de ces crues sont les quantiles décennal et centennal des débits moyens mensuels maximaux annuels (QMXA). Ainsi, un scénario optimiste de prévision climatique a été utilisé (RCP 2.6). Ce scénario climatique a ensuite alimenté un modèle hydrologique pluie-débit (modèle GR2M) calé sur la période de référence 1961-1990 et validé sur la période 1991-2017. En réponse au forçage climatique, les débits mensuels de crue (QMXA) futurs ont été simulés. Les principaux résultats montrent que la meilleure loi statistique retenue à la suite de l’analyse fréquentielle des débits de crue est la loi Gamma qui a servi à l’estimation des débits fréquentiels. Le modèle GR2M évalué, a présenté une bonne performance en calage (79,7%) comme en validation (82,7%) et a démontré une grande robustesse (+3%) donc une grande capacité à reconstituer les débits du N’zo à Kahin. La prospective climatique a mis en évidence une baisse des précipitations (-19,7%) et une augmentation de la température (+1,6 °C) au milieu du siècle en cours (2036-2065). Les quantiles de débit de crue attendus au milieu du 21ème siècle (2035-2065) sont respectivement de 168,85 m3/s pour le débit décennal et 299,58 m3/s pour le débit centennal. Ainsi, en réponse aux changements climatiques, la prospective des débits de crue conduit à une baisse préoccupante des débits fréquentiels de crue respectivement de l’ordre de 64,56% pour la crue décennale et 61,73% pour la crue centennale par rapport à leurs valeurs actuelles.
Author Keywords: Changements climatiques, Prospective hydrologique, Débits de crue (QMXA), Modèle GR2M, N’zo-Sassandra, Côte d’Ivoire.
How to Cite this Article
Amani Michel Kouassi, Gnangouin Asaph Yahot Joel, Yao Charles Armel, and N’Guessan N’Guessan Emilienne, “Prospective impact study of flood flows in a context of climate change in West Africa: Case of the N’zo watershed (Sassandra, West of Ivory Coast),” International Journal of Innovation and Scientific Research, vol. 57, no. 2, pp. 117–131, November 2021.
