The aim of this study is to understand the inter-annual hydrological variability (precipitation a... more The aim of this study is to understand the inter-annual hydrological variability (precipitation and streamflow) in the basins of the High Atlas in Morocco and to determine how climate fluctuations (represented by the North Atlantic Oscillation (NAO) climate index) are expressed in the hydrological system. To reach this objective, time series of precipitation and streamflow are processed as standardized anomalies and studied by continuous wavelet analysis and wavelet coherence analysis, which are particularly suitable for the study of unsteady processes. Wet and dry periods vary from one basin to another between three and five years. The wavelet analysis shows the existence of many bands of energy in most of the sub-basins, from annual to inter-annual scales regarding the precipitation and streamflow time series. These bands correspond to intervals of one year, 2–4 years, 4–8 years and 8–12 years. The wavelet coherence analysis shows a strong coherence between NAO/streamflow and precipitation/NAO identified at the inter-annual scale. Non-stationarity can be observed in the late 1980s, 1990s and 2000s. The contribution of the NAO is different from one basin to another ranging between 67% and 77%.
Tirés à part : G. Mahé Résumé Le bassin du Nakambe à Wayen (Burkina Faso) occupe une surface de p... more Tirés à part : G. Mahé Résumé Le bassin du Nakambe à Wayen (Burkina Faso) occupe une surface de près de 21 000 km 2 en domaine sahélien. Malgré la baisse de la pluviométrie depuis 1970, ses débits de pointe et ses coefficients d'écoulement augmentent régulière-ment. Les crues sont plus précoces – en août au lieu de septembre – et plus intenses. Cette augmentation est également observée pour d'autres cours d'eau sahéliens voisins. Les débits journaliers maximums augmentent de près de 100 %, mais le nombre de jours où le débit est supérieur à la moitié du débit maximum varie peu sur la même période, traduisant une crue peu étalée dans le temps. Cette augmen-tation des écoulements est liée à la pression démographique et à la forte diminution des zones de végétation naturelle, remplacées par des cultures et des sols nus dont la capacité au ruissellement est supérieure.
Baisse des pluies et augmentation des e ´coulements au Sahel : impact climatique et anthropique s... more Baisse des pluies et augmentation des e ´coulements au Sahel : impact climatique et anthropique sur les e ´coulements du Nakambe au Burkina Faso Résumé Le bassin du Nakambe à Wayen (Burkina-Faso) occupe une surface de près de 21 000 km 2 en domaine sahélien. Malgré la baisse de la pluviométrie depuis 1970, ses débits de pointe et ses coefficients d'écoulement augmentent régulière-ment. Les crues sont plus précoces, en août au lieu de septembre, et plus intenses. Cette augmentation est également observée pour d'autres cours d'eau sahéliens voisins. Les débits journaliers maximums augmentent de près de 100 %, mais le nombre de jours où le débit est supérieur à la moitié du débit maximum varie peu sur la même période, traduisant une crue peu étalée dans le temps. Cette augmen-tation des écoulements est liée à la pression démographique et à la forte diminution des zones de végétation naturelle, remplacées par des cultures et des sols nus, dont la capacité au ruissellement es...
... Hydrologie des régions méditerra-néennes semi-arides. AISH Publ. 278. AISH, 2003. Cultures Ét... more ... Hydrologie des régions méditerra-néennes semi-arides. AISH Publ. 278. AISH, 2003. Cultures États de surface Occupation des terres en 1972 Sol nu Surface en eau Végétation Cultures États de surface Occupation des terres en 1986 Sol nu Surface en eau Végétation ...
The drought that prevails in the Sahel since the seventies
has significantly reduced the producti... more The drought that prevails in the Sahel since the seventies has significantly reduced the production in all sectors. In the Inner Niger Delta in Mali (DIN), fishing whose development is closely linked with the inter-seasonal and inter-annual fluctuations of the flood of the river Niger, is still in a deep crisis. Catches have declined by half, many fishermen left, some have adopted unsustainable practices and social rules are collapsing. The results obtained show that fishermen have an accurate perception of the flood and its evolution along the time. The total annual catch has dropped considerably and almost all fishermen agree that this decline is related not only to the amount collected, but also to the quality of the catches. Accordingly, 40 % of the fishermen relegated fishing to the row of ancillary activity and 35 % diversified their activities into agriculture, trade or transport. However, few fishermen of DIN imagine their lives under conditions of profound changes of the flood of the river Niger.
The aim of this study is to understand the inter-annual hydrological variability (precipitation a... more The aim of this study is to understand the inter-annual hydrological variability (precipitation and streamflow) in the basins of the High Atlas in Morocco and to determine how climate fluctuations (represented by the North Atlantic Oscillation (NAO) climate index) are expressed in the hydrological system. To reach this objective, time series of precipitation and streamflow are processed as standardized anomalies and studied by continuous wavelet analysis and wavelet coherence analysis, which are particularly suitable for the study of unsteady processes. Wet and dry periods vary from one basin to another between three and five years. The wavelet analysis shows the existence of many bands of energy in most of the sub-basins, from annual to inter-annual scales regarding the precipitation and streamflow time series. These bands correspond to intervals of one year, 2–4 years, 4–8 years and 8–12 years. The wavelet coherence analysis shows a strong coherence between NAO/streamflow and precipitation/NAO identified at the inter-annual scale. Non-stationarity can be observed in the late 1980s, 1990s and 2000s. The contribution of the NAO is different from one basin to another ranging between 67% and 77%.
Tirés à part : G. Mahé Résumé Le bassin du Nakambe à Wayen (Burkina Faso) occupe une surface de p... more Tirés à part : G. Mahé Résumé Le bassin du Nakambe à Wayen (Burkina Faso) occupe une surface de près de 21 000 km 2 en domaine sahélien. Malgré la baisse de la pluviométrie depuis 1970, ses débits de pointe et ses coefficients d'écoulement augmentent régulière-ment. Les crues sont plus précoces – en août au lieu de septembre – et plus intenses. Cette augmentation est également observée pour d'autres cours d'eau sahéliens voisins. Les débits journaliers maximums augmentent de près de 100 %, mais le nombre de jours où le débit est supérieur à la moitié du débit maximum varie peu sur la même période, traduisant une crue peu étalée dans le temps. Cette augmen-tation des écoulements est liée à la pression démographique et à la forte diminution des zones de végétation naturelle, remplacées par des cultures et des sols nus dont la capacité au ruissellement est supérieure.
Baisse des pluies et augmentation des e ´coulements au Sahel : impact climatique et anthropique s... more Baisse des pluies et augmentation des e ´coulements au Sahel : impact climatique et anthropique sur les e ´coulements du Nakambe au Burkina Faso Résumé Le bassin du Nakambe à Wayen (Burkina-Faso) occupe une surface de près de 21 000 km 2 en domaine sahélien. Malgré la baisse de la pluviométrie depuis 1970, ses débits de pointe et ses coefficients d'écoulement augmentent régulière-ment. Les crues sont plus précoces, en août au lieu de septembre, et plus intenses. Cette augmentation est également observée pour d'autres cours d'eau sahéliens voisins. Les débits journaliers maximums augmentent de près de 100 %, mais le nombre de jours où le débit est supérieur à la moitié du débit maximum varie peu sur la même période, traduisant une crue peu étalée dans le temps. Cette augmen-tation des écoulements est liée à la pression démographique et à la forte diminution des zones de végétation naturelle, remplacées par des cultures et des sols nus, dont la capacité au ruissellement es...
... Hydrologie des régions méditerra-néennes semi-arides. AISH Publ. 278. AISH, 2003. Cultures Ét... more ... Hydrologie des régions méditerra-néennes semi-arides. AISH Publ. 278. AISH, 2003. Cultures États de surface Occupation des terres en 1972 Sol nu Surface en eau Végétation Cultures États de surface Occupation des terres en 1986 Sol nu Surface en eau Végétation ...
The drought that prevails in the Sahel since the seventies
has significantly reduced the producti... more The drought that prevails in the Sahel since the seventies has significantly reduced the production in all sectors. In the Inner Niger Delta in Mali (DIN), fishing whose development is closely linked with the inter-seasonal and inter-annual fluctuations of the flood of the river Niger, is still in a deep crisis. Catches have declined by half, many fishermen left, some have adopted unsustainable practices and social rules are collapsing. The results obtained show that fishermen have an accurate perception of the flood and its evolution along the time. The total annual catch has dropped considerably and almost all fishermen agree that this decline is related not only to the amount collected, but also to the quality of the catches. Accordingly, 40 % of the fishermen relegated fishing to the row of ancillary activity and 35 % diversified their activities into agriculture, trade or transport. However, few fishermen of DIN imagine their lives under conditions of profound changes of the flood of the river Niger.
Uploads
has significantly reduced the production in all sectors. In
the Inner Niger Delta in Mali (DIN), fishing whose
development is closely linked with the inter-seasonal and
inter-annual fluctuations of the flood of the river Niger, is
still in a deep crisis. Catches have declined by half, many
fishermen left, some have adopted unsustainable practices
and social rules are collapsing. The results obtained show
that fishermen have an accurate perception of the flood
and its evolution along the time. The total annual catch
has dropped considerably and almost all fishermen agree
that this decline is related not only to the amount collected,
but also to the quality of the catches. Accordingly, 40 %
of the fishermen relegated fishing to the row of ancillary
activity and 35 % diversified their activities into agriculture,
trade or transport. However, few fishermen of DIN
imagine their lives under conditions of profound changes
of the flood of the river Niger.
has significantly reduced the production in all sectors. In
the Inner Niger Delta in Mali (DIN), fishing whose
development is closely linked with the inter-seasonal and
inter-annual fluctuations of the flood of the river Niger, is
still in a deep crisis. Catches have declined by half, many
fishermen left, some have adopted unsustainable practices
and social rules are collapsing. The results obtained show
that fishermen have an accurate perception of the flood
and its evolution along the time. The total annual catch
has dropped considerably and almost all fishermen agree
that this decline is related not only to the amount collected,
but also to the quality of the catches. Accordingly, 40 %
of the fishermen relegated fishing to the row of ancillary
activity and 35 % diversified their activities into agriculture,
trade or transport. However, few fishermen of DIN
imagine their lives under conditions of profound changes
of the flood of the river Niger.