Relationship between soil water content and crop yield under sahelian climate conditions: case study of Tougou experimental site in Burkina Faso

This study aims at assessing the relationship between soil water stock and the yield of agricultural practices in Tougou catchment located in northern Burkina Faso. It is a region that has experienced a significant and continuous degradation of its natural resources, especially soils, due to the climate variability and the rapid increase of the population. Areas allocated to subsistence agriculture are increasing at the expense of pastoral land. This degradation causes a change in processes and mechanisms that control ecological systems. In order to provide solutions to this issue, some agricultural practices have been implemented to improve crop yield. This is particularly the case of traditional techniques:za, stony line and half-moon, which can significantly improve the soil infiltration capacity and yield. Daily monitoring of soil moisture and pressure in experimental plots based on these agricultural practices show that half-moon and Za¯ provided good yield with 2180kg / ha and 1070 kg / ha respectively compared to that of the control plot with about 480 kg/ha. These important yields are due in large part to the improvement of the retention capacity of these soils, thus giving to crops the necessary water need for their development even in drought period

Establishment of Dynamic Evolving Neural-Fuzzy Inference System Model for Natural Air Temperature Prediction

Air temperature (AT) prediction can play a significant role in studies related to climate change, radiation and heat flux estimation, and weather forecasting. This study applied and compared the outcomes of three advanced fuzzy inference models, i.e., dynamic evolving neural-fuzzy inference system (DENFIS), hybrid neural-fuzzy inference system (HyFIS), and adaptive neurofuzzy inference system (ANFIS) for AT prediction. Modelling was done for three stations in North Dakota (ND), USA, i.e., Robinson, Ada, and Hillsboro. The results reveal that FIS type models are well suited when handling highly variable data, such as AT, which shows a high positive correlation with average daily dew point (DP), total solar radiation (TSR), and negative correlation with average wind speed (WS). At the Robinson station, DENFIS performed the best with a coefficient of determination (R$^{2}$) of 0.96 and a modified index of agreement (md) of 0.92, followed by ANFIS with R$^{2}$ of 0.94 and md of 0.89, and HyFIS with R$^{2}$ of 0.90 and md of 0.84. A similar result was observed for the other two stations, i.e., Ada and Hillsboro stations where DENFIS performed the best with R$^{2}$: 0.953/0.960, md: 0.903/0.912, then ANFIS with R$^{2}$: 0.943/0.942, md: 0.888/0.890, and HyFIS with R$^{2}$ 0.908/0.905, md: 0.845/0.821, respectively. It can be concluded that all three models are capable of predicting AT with high efficiency by only using DP, TSR, and WS as input variables. This makes the application of these models more reliable for a meteorological variable with the need for the least number of input variables. The study can be valuable for the areas where the climatological and seasonal variations are studied and will allow providing excellent prediction results with the least error margin and without a huge expenditure

Dynamique spatio-temporelle des états de surface et influence sur le ruissellement sur un bassin de type sahélien: cas du bassin de Tougou (Nord Burkina Faso)

La dynamique spatio-temporelle des états de surface est un facteur déterminant de la réponse hydrologique d’un bassin versant. Ce constat se pose avec plus d’acuité dans le cas des hydrosystèmes sahéliens, où il est avéré que les processus de génération du ruissellement de surface sont sous la quasi-dépendance des états de surface du sol. Parmi les données d’entrée, la modélisation hydrologique nécessite la cartographie de l’occupation des sols sur l’espace de simulation. Cette donnée est d’une importance particulière car elle indique au modèle l’organisation du paysage et lui permet d’intégrer la variabilité spatiale au cœur des processus hydrologiques à simuler. Cependant, dans la pratique, une couche unique d’états de surface est en général fournie au modèle hydrologique et reste statique pour une simulation souvent conduite de longue durée (de l’ordre de plusieurs dizaines d’années). Si en général, en raison de l’équifinalité des paramètres de modélisation, on arrive toujours à représenter les données observées, cela se traduit par un biais de précision sur l’allure temporelle des flux hydrologiques simulés, qui peut être significatif.Cette étude vise à apporter une contribution à la quantification de l’impact de la dynamique spatio-temporelle des états de surface sur le ruissellement dans le contexte des hydrosystèmes sahéliens. Le bassin versant sahélien de Tougou (37 km²), situé dans la province du Yatenga (dans la Région du Nord, Burkina Faso) a été retenu comme cadre d’étude. La cartographie du paysage du bassin versant a été reconstituée de 1952 à 2017 par la télédétection. Une analyse diachronique a permis de quantifier l’intensité de transformation du paysage, qui a pu être mise en lien avec l’évolution de la pluviométrie et la pression anthropique sur la même période. Il apparait principalement que de 1952 à 2017 sur le bassin de Tougou, la végétation naturelle a significativement diminué (de 46 à 2,5%) tandis que les sols dégradés et cultivés ont connu une expansion (de 3 à 33,5% et de 51 à 64%, respectivement). L’évolution spatiale du bassin a été projetée à l’horizon 2050, à l’aide d’un réseau de neurones artificiel et de perspectives démographiques, annonçant une hausse des sols cultivés à 90,2% de l’espace du bassin.Les implications hydrologiques de cette dynamique spatio-temporelle des états de surface ont été ensuite évalués par la modélisation hydrologique. À cet effet, le modèle agro-hydrologique SWAT (Soil & Water Assessment Tool) a été calibré et validé sur des données observées de ruissellement, collectées sur la période 2004-2018, à l’exutoire du bassin versant. Les simulations ont été conduites sous deux scénarios : un scénario utilisant une carte statique des états de surface (en 1999), correspondant à l’approche classique de modélisation hydrologique ; un second scénario intégrant de façon dynamique l’évolution des états de surface sur le bassin de 1999 à 2017. Ce second scénario a permis une reproduction plus précise du ruissellement observé (aux pas de temps journalier, mensuel, annuel), mais aussi une estimation plus objective d’autres processus hydrologiques tels que l’évapotranspiration réelle et la recharge profonde.En se servant des paramètres de modélisation calibrés en scénario dynamique, les écoulements sur le bassin versant de Tougou ont été reconstitués sur la période historique 1952-2005. À ce stade, il a pu être montré à nouveau que seule l’intégration de la dynamique spatio-temporelle des états de surface permettait de reproduire le paradoxe hydrologique des hydrosystèmes sahéliens, bien connu des hydrologues. Ensuite, en analysant les contributions isolées du climat et des états de surface sur la hausse du ruissellement entre les sous périodes 1952-1968 et 1986-2005, il apparait que l’impact de la dynamique des états de surface domine sur celui de la variabilité du climat. En ce qui concerne l’évolution future du bassin de Tougou dans un contexte de changement climatique, un ensemble de 5 modèles régionaux (issus de CORDEX-Africa) a été constitué dans le cadre de cette étude. Cet ensemble prévoit, à l’horizon 2050, une baisse non significative de la pluie (2,3 à 3%) et une hausse significative de l’évapotranspiration potentielle (5 à 6%). En considérant également l’augmentation projetée pour les sols cultivés, l’écoulement moyen annuel est projeté en baisse en scénario RCP4.5 (11,7%), principalement causé par l’augmentation des sols cultivés. Par contre, en scénario RCP8.5, une légère hausse de l’écoulement moyen annuel (0,6%) est projetée, attribuable à l’intensification de la pluie, qui domine alors sur l’effet de la dynamique des états de surface.En définitive, les résultats de cette étude permettent d’interpeller les hydrologues et dans une plus large mesure, les acteurs de la gestion et de la planification de la ressource en eau. Cette étude sert de plaidoyer en faveur du suivi de l’évolution spatio-temporelle des états de surface, mais aussi du couplage de cette information dans la modélisation hydrologique en tant que nouvelle pratique. Aussi, la recherche devrait s’orienter vers le développement d’outils et de plateformes de modélisation intégrées prenant en considération ces aspects, afin de permettre une meilleure prévision de la ressource en eau, en particulier dans le cas des hydrosystèmes sahéliens.Land use/land cover (LULC) changes is a major factor explaining the hydrological response of a watershed. Such observation stands more acutely in the case of Sahelian hydrosystems, where it acknowledged that surface runoff generation processes are typically dependent on soil surface conditions.Hydrological modelling requires a LULC map of the simulation space among the input data. This information is of particular importance as it indicates to the model the organization of the landscape and allows seamless integration of spatial variability in the simulation of hydrological processes. However, in practice, a single LULC map is usually provided to the model and remains static for a simulation that is often conducted over a long period (up several tens of years). Eventually, due to the equifinality of the modelling parameters, the model always manages to represent the observed data. However, this results in biases on the temporal patterns of the simulated processes, which can be significant.This study aims to contribute to the quantification of the impact of LULC changes on surface runoff in the context of Sahelian hydrosystems. The Tougou watershed (37 km²), located in the province of Yatenga (in the Northern Region, Burkina Faso) is selected as a case study. LULC maps of the watershed are produced from 1952 to 2017 through remote sensing. LULC change analysis revealed the intensity of the landscape transformation, which is related to the evolution of rainfall and anthropic pressure over the same period. It mainly appears that from 1952 to 2017 in the Tougou watershed, the natural vegetation significantly decreased (from 46 to 2.5%) while bare/degraded and cultivated soils expanded (from 3 to 33.5% and 51 to 64%, respectively). The spatial development of the basin is projected for 2050, using an artificial neural network and demographic perspectives, predicting an increase in cultivated soils to 90.2% of the watershed area.The hydrological implications of these LULC dynamics are assessed through hydrological modelling. To this end, the SWAT (Soil & Water Assessment Tool) model is calibrated and validated on observed runoff data, collected over the period 2004-2018, at the watershed outlet. The simulations are carried out under two scenarios: a scenario using a static LULC map (in 1999), corresponding to the classical modelling approach; a second scenario, integrating dynamically the observed LULC trends in the watershed from 1999 to 2017. This second scenario allows a more precise simulation of the observed runoff (at daily, monthly, annual time scales), but also a better estimate of other processes such as actual evapotranspiration and deep recharge.Using calibrated parameters in the dynamic scenario, surface runoff over the Tougou watershed were reconstructed over the historical period 1952-2005. At this stage, it is shown once again that only the integration of the LULC dynamics helps in reproducing the Sahelian hydrological paradox, well known to hydrologists. Therefore, by analysing the isolated contributions of climate variability and LULC changes on the increase in runoff between the sub-periods 1952-1968 and 1986-2005, it appears that the impact of LULC changes is dominant over the climate variability.Regarding the future evolution of the Tougou basin in the face of climate change, an ensemble of five (5) regional models (from the CORDEX-Africa package) was constructed as part of this study. This ensemble projects, by 2050, a non-significant decrease in rainfall (2.3 to 3%) and a significant increase in potential evapotranspiration (5 to 6%). Considering the projected increase for cultivated soils, the average annual runoff is projected to decrease in the RCP4.5 scenario (by 11.7%), mainly caused by the increase in cultivated soils (LULC change). In opposite, in the RCP8.5 scenario, a slight increase in the mean annual runoff (by 0.6%) is projected, attributable to the intensification of rainfall, which tends to dominate the effect of the increase in cultivated soils (LULC change).The results of this study call to hydrologists and, to a greater extent, planners and managers of water resources. This study stands a pledge in favour of the monitoring of LULC trends and change at the watershed scale, but also the coupling of this information in hydrological modelling as a new practice. Also, research should be directed towards the development of integrated modelling tools and platforms to this end, to allow better forecasting of water resources, in particular in the case of Sahelian hydrosystems

Unravelling the Impacts of Climate Variability on Surface Runoff in the Mouhoun River Catchment (West Africa)

This study assesses the impacts of climate variability on surface runoff generation in the Mouhoun River Catchment (MRC) in Burkina Faso, in the West African Sahel. The study uses a combination of observed and reanalysis data over the period 1983–2018 to develop a SWAT model (KGE = 0.77/0.89 in calibration/validation) further used to reconstitute the complete time series for surface runoff. Results show that annual rainfall and surface runoff follow a significant upward trend (rainfall: 4.98 mm·year−1, p-value = 0.029; runoff: 0.45 m3·s−1·year−1, p-value = 0.013). Also, rainfall appears to be the dominant driver of surface runoff (Spearman’s ρ = 0.732, p-value p-value = 0.386). The study highlights the added value of the coupling of hydrological modeling and reanalysis datasets to analyze the rainfall–runoff relationship in data-scarce and poorly gauged environments and therefore raises pathways to improve knowledge and understanding of the impacts of climate variability in Sahelian hydrosystems

Influence des changements d’utilisation des terres sur les débits du bassin versant du Massili à Gonsé (Burkina Faso)

This study aims to determine the contribution of land use changes on runoff in the Massili basin in Gonsé. The study methodology is based on the analysis of the temporal variability of rainfall (1975-2019) and discharge (1975-2019) and the diachronic analysis of land use (1975-1991-2007-2019). The statistical tools used are Pettitt’s test, Hubert’s segmentation procedure, Mann-Kendall test and Pearson’s correlation test. The results show that the Massili catchment area experienced a long dry period from 1975-2001 and a wet phase from 2002-2019. The breakpoint detection test highlighted changepoints in 2002 and 2003 (Pettitt), 2004, 2008 and 2019 (Hubert’s segmentation) with increase ranging from 64,55% to 95,76% after the breaks. Significant upward trends were observed for monthly and annual flows. The Pearson test reveals a low correlation between rainfall and discharge with values between 0,141 and 0,225. These findings show that the evolution discharge is affected by the regression rate of the savannahs of -79,69% and riparian formations of -14,84%, to the benefit for urban areas of 1006,65%, the bare soil of 388,92% and agricultural area of 79,92%, favorable to runoff. The results shed light on the causes of streamflow variability and might be useful in framing integrated land and water resources management policies

Quantification of Soil Deep Drainage and Aquifer Recharge Dynamics according to Land Use and Land Cover in the Basement Zone of Burkina Faso in West Africa

Groundwater is a vital water supply for local populations and ecosystems globally. With the continuous population growth, the anthropic pressure on groundwater is ever increasing, thus reducing the amount of available water resource. Yet, estimating the impact of anthropogenic activities on aquifer recharge is still a significant challenge for research, especially in basement aquifers. This study aims to improve the actual knowledge of deep drainage and deep aquifer recharge pathways and dynamics in the basement as affected by land use/land cover (LULC). The methodology used in this study accounted for hydraulic processes in soil layers within both unsaturated and saturated zones in an integrated approach. An experimental setup consisting of three (3) experimental plots, respectively under natural vegetation (NV), cropped millet (CM) and cropped groundnut (CG) on which deep drainage was monitored during the years 2020 and 2021. The results show significant differences between the LULC types after two years of implementation. Deep drainage is improved under CM and CG plots located in the central valley, as compared to the NV plot located in the ridge zone. Deep drainage is estimated at 8%, 24% and 25% of the annual rainfall, respectively for NV, CM and CG. The ratio between the recharge value obtained by the water table fluctuation (WTF) method and the deep drainage tends to 1 for the CM and CG plots, highlighting a rapid water transfer between unsaturated and saturated zones. The central valley, which seems to be a preferential recharge pathway, provides promising insights under specific conditions for the implementation of artificial recharge infrastructures

Influence des changements d’utilisation des terres sur les débits du bassin versant du Massili à Gonsé (Burkina Faso)

La présente étude vise à déterminer la contribution des changements d’utilisation des terres sur les écoulements dans le bassin du Massili à Gonsé (Burkina Faso). Elle s’appuie sur l’étude de la variabilité temporelle des précipitations (1975-2019) et des débits (1975-2019) et l’analyse diachronique de l’occupation des terres (1975-1991-2007-2019). Les outils statistiques utilisés sont les tests de Pettitt, la segmentation de Hubert, le test de Mann-Kendall et le test de corrélation de Pearson. Les résultats montrent que le bassin versant du Massili a connu une longue période sèche de 1975 à 2001 et une phase humide de 2002 à 2019. L’analyse des débits a permis d’identifier des ruptures en 2002 et 2003 (Pettitt) et 2004, 2008 et 2019 (Segmentation de Hubert) avec des hausses comprises entre 64,55% à 95,76% après les ruptures. Des tendances significatives à la hausse ont été observées sur les débits mensuels et annuels. Le test de Pearson révèle une faible corrélation entre la pluie et les débits avec des valeurs comprises entre 0,141-0,225. La tendance des débits est en relation avec la dynamique de l’occupation des terres marquée par un taux de régression de -79,69% des savanes et de -14,84% des formations ripicoles, au bénéfice de l’habitat de 1006,65%, des sols nus de 388,92% et des zones de culture de 79,92%, favorables au ruissellement. Ces résultats apportent des éléments indicatifs sur les causes de variabilité des écoulements et sont utiles pour la gestion intégrée des sols et des ressources en eau du bassin de Gonsé.This study aims to determine the contribution of land use changes on runoff in the Massili basin in Gonsé. The study methodology is based on the analysis of the temporal variability of rainfall (1975-2019) and discharge (1975-2019) and the diachronic analysis of land use (1975-1991-2007-2019). The statistical tools used are Pettitt’s test, Hubert’s segmentation procedure, Mann-Kendall test and Pearson’s correlation test. The results show that the Massili catchment area experienced a long dry period from 1975-2001 and a wet phase from 2002-2019. The breakpoint detection test highlighted changepoints in 2002 and 2003 (Pettitt), 2004, 2008 and 2019 (Hubert’s segmentation) with increase ranging from 64,55% to 95,76% after the breaks. Significant upward trends were observed for monthly and annual flows. The Pearson test reveals a low correlation between rainfall and discharge with values between 0,141 and 0,225. These findings show that the evolution discharge is affected by the regression rate of the savannahs of -79,69% and riparian formations of -14,84%, to the benefit for urban areas of 1006,65%, the bare soil of 388,92% and agricultural area of 79,92%, favorable to runoff. The results shed light on the causes of streamflow variability and might be useful in framing integrated land and water resources management policies

Quantification of Soil Deep Drainage and Aquifer Recharge Dynamics according to Land Use and Land Cover in the Basement Zone of Burkina Faso in West Africa

Groundwater is a vital water supply for local populations and ecosystems globally. With the continuous population growth, the anthropic pressure on groundwater is ever increasing, thus reducing the amount of available water resource. Yet, estimating the impact of anthropogenic activities on aquifer recharge is still a significant challenge for research, especially in basement aquifers. This study aims to improve the actual knowledge of deep drainage and deep aquifer recharge pathways and dynamics in the basement as affected by land use/land cover (LULC). The methodology used in this study accounted for hydraulic processes in soil layers within both unsaturated and saturated zones in an integrated approach. An experimental setup consisting of three (3) experimental plots, respectively under natural vegetation (NV), cropped millet (CM) and cropped groundnut (CG) on which deep drainage was monitored during the years 2020 and 2021. The results show significant differences between the LULC types after two years of implementation. Deep drainage is improved under CM and CG plots located in the central valley, as compared to the NV plot located in the ridge zone. Deep drainage is estimated at 8%, 24% and 25% of the annual rainfall, respectively for NV, CM and CG. The ratio between the recharge value obtained by the water table fluctuation (WTF) method and the deep drainage tends to 1 for the CM and CG plots, highlighting a rapid water transfer between unsaturated and saturated zones. The central valley, which seems to be a preferential recharge pathway, provides promising insights under specific conditions for the implementation of artificial recharge infrastructures