Climate Normalized Spatial Patterns of Evapotranspiration Enhance the Calibration of a Hydrological Model

Spatial pattern-oriented evaluations of distributed hydrological models have contributed towards an improved realism of hydrological simulations. This advancement has been supported by the broad range of readily available satellite-based datasets of key hydrological variables, such as evapotranspiration (ET). At larger scale, spatial patterns of ET are often driven by underlying climate gradients, and with this study, we argue that gradient dominated patterns may hamper the potential of spatial pattern-oriented evaluation frameworks. We hypothesize that the climate control of spatial patterns of ET overshadows the effect model parameters have on the simulated patterns. To address this, we propose a climate normalization strategy. This is demonstrated for the Senegal River basin as a modeling case study, where the dominant north-south precipitation gradient is the main driver of the observed hydrological variability. We apply the mesoscale Hydrological Model (mHM) to model the hydrological cycle of the Senegal River basin. Two multi-objective calibration experiments investigate the effect of climate normalization. Both calibrations utilize observed discharge (Q) in combination with remote sensing ET data, where one is based on the original ET pattern and the other utilizes the normalized ET pattern. As objective functions we applied the Kling-Gupta-Efficiency (KGE) for Q and the Spatial Efficiency (SPAEF) for ET. We identify parameter sets that balance the tradeoffs between the two independent observations and find that the calibration using the normalized ET pattern does not compromise the spatial pattern performance of the original pattern. However, vice versa, this is not necessarily the case, since the calibration using the original ET pattern showed a poorer performance for the normalized pattern, i.e., a 30% decrease in SPAEF. Both calibrations reached comparable performance of Q, i.e., KGE around 0.7. With this study, we identified a general shortcoming of spatial pattern-oriented model evaluations using ET in basins dominated by a climate gradient, but we argue that this also applies to other variables such as, soil moisture or land surface temperature.

Determination of the Hydrodynamic Parameters of Two Types of Soil in the Senegal River Delta. Simulation of Hydro-saline Transfers: Application to the Wind Deflation Phenomenon

In the Senegal River delta, the presence of a shallow salt water table associated with a strong evaporative demand sometimes leads to an upwelling of salts that crystallize on the surface. This phenomenon can be observed in the vicinity of the Diawling Basin, where a powdery structure sensitive to wind deflation and a massive structure with a fractionation into platelets that cannot be transported by the wind are noted. To understand the hydrodynamic characteristics of these soils, we used numerical simulation of water and solute transfers. The hydrodynamic parameters were determined in the laboratory using Wind's method on undisturbed samples. The experimental retention h() and hydraulic conductivity K(h) curves were fitted using the Van Genuchten model. The simulations show that the soil with a powdery structure has hydrodynamic characteristics that favour the ascent of salts from the water table to the surface. For the soil with a massive structure, the hydrodynamic conditions impose a deposition of salts in the subsurface.

Low Malaria Transmission in Rosso, an Irrigated Rice-Growing Area in Mauritania

The construction of dams along the Senegal River resulted in an increase in irrigated land areas and changes in the epidemiology and transmission of water-related diseases. The objective of this study was to update epidemiological data on malaria in Rosso, one of the major Mauritanian cities along the Senegal River. Febrile patients (n = 318) were screened for malaria using a rapid diagnostic test (RDT) for malaria and microscopic examination of blood smears. Diagnosis was later confirmed by polymerase chain reaction (PCR). The mean age of 318 febrile patients was 25.1 (range 1–80 years). Only 7 (2.2%) and 2 (0.6%) had a positive RDT and thick smear, respectively. PCR confirmed the diagnosis in two Plasmodium vivax-infected patients. Most participants (198/318, 62.3%) had no recent travel history outside Rosso. The majority of the febrile patients (90%, 284/311) owned at least one insecticide-treated net (ITN). The frequency of the use of ITNs was not significantly associated with season (rainy vs. dry seasons; p = 0.9) or with the number of ITNs per household (rs = 0.07; n = 285; p = 0.19). Of 285 individuals with ITNs, only two (0.7%) with no travel history were PCR-positive for malaria. Despite the presence of mosquito breeding sites related to rice irrigation, malaria transmission in Rosso remained very low, possibly due to the high coverage and frequent use of bed nets. Regular entomological surveillance for possible changes in the prevalence of Anopheles mosquito species and their behavioural aspects should be implemented.

1970s Drought, State Crisis, and Opportunities for Transnational River Development in the Senegal Basin

During the early 1970s, the Sahel suffered from drought and famine. Previous research has emphasized how these factors weakened West African states. The drought, however, provided an opportunity for a transnational river organization in the Senegal River basin (the OMVS) to obtain financing for an integrated development program. Wall shows how the OMVS leveraged concern about famine to obtain funding. She uses digital text analysis to demonstrate institutional priorities shifting to focus on agriculture. This combination of document analysis with digital methods demonstrates how famine strengthened a multi-state organization, requiring a revision of how this event affected African political capacity.

Exploitation de l’espece Anadara Senilis (Arches) dans le Parc National de la Langue de Barbarie (PNLB), Gandiol (Senegal)

Dans l’espace du Gandiol, les activités économiques traditionnelles étaient la pêche et l’agriculture avec lesquelles la population a une longue tradition. En 2003, les fortes pluies enregistrées dans le Haut bassin du fleuve Sénégal expliquent l’augmentation massive du débit du fleuve consécutivement à l’addition des ondes de crue. Pour empêcher des inondations dans la ville de Saint-Louis, une brèche a été ouverte. Cependant, cette brèche a eu des effets négatifs sur l’agriculture et beaucoup d’espèces de poissons. Elle a, aussi, entrainé des modifications écologiques se manifestant par l’apparition de certaines espèces aquatiques : Anadara Senilis, Carasostrea Gasar. Dès lors, l’étude de l’exploitation de l’espèce Anadara senilis dans le parc national de la langue de Barbarie (commune de Ndiebène Gandiol) fait l’objet de cette contribution. La méthodologie adoptée intègre les enquêtes de terrain sous forme de questionnaires et de guides d’entretien et le traitement des données quantitatives et qualitatives. Les résultats montrent que la collecte des coquillages est progressivement devenue la principale activité des femmes. Cette activité est pratiquée dans un but essentiellement lucratif et a eu des impacts considérables tant au niveau socioéconomique qu’environnemental. C’est pourquoi, l’encadrement des exploitants est souhaitable pour une gestion durable de cette ressource renouvelable. In the Gandiol area, the traditional economic activities were fishing and agriculture, with which the population has a long tradition. In 2003, the heavy rains recorded in the upper Senegal River basin explain the massive increase in the river's flow following the addition of flood waves. To prevent flooding in the city of Saint-Louis, a breach was opened. However, this breach had negative effects on agriculture and many fish species. It has also caused ecological changes manifested by the appearance of certain aquatic species: Anadara Senilis, Carasostrea Gasar. Therefore, the study of the exploitation of the species Anadara senilis in the National Park of the Langue de Barbarie (municipality of Ndiebène Gandiol) is the subject of this contribution. The methodology adopted integrates field surveys in the form of questionnaires and interview guides and the processing of quantitative and qualitative data. The results show that shellfish collection has gradually become the main activity of women. This activity is practiced essentially for profit and has had considerable impacts at both the socio-economic and environmental levels. This is why the supervision of the operators is desirable for a sustainable management of this renewable resource.

Changements historiques à long terme du débit écoulé dans le Haut bassin du fleuve Sénégal

In this study, the flow trends on either side of the Manantali dam, in the upper Senegal River basin, were assessed. The assessment was carried out for the period 1970 to 2019 using the Sen slope and the Mann-Kendall test. The Mann-Kendall trend test was used to indicate the direction of the trends, while the Sen slope was used to assess the magnitude of the change. The results of the study showed that there was an upward trend in the flow of the Senegal River both annually and for every month upstream (Bafing-Makana station) and downstream (Bakel station) from the barrage. The strongest upward trend is noted in October on the upstream station with 4.12 m3/month and in September on the downstream station with 10.99 m3/month. In return, the weakest upward trend is observed in May on the upstream station with 0.07 m3/month and in August on the downstream station with 0.67 m3/month. The annual flow also showed a significant increase upstream (with a rate of 0.35 m3/year) and downstream (with a rate of 4.53 m3/year) with a confidence level of 99 %. The results of the study also showed that an increase in precipitation causes an increase in runoff, despite the construction of hydraulic structures.

Climate Normalized Spatial Patterns of Evapotranspiration Enhance the Evaluation of Hydrological Models

Spatial pattern-oriented evaluations of distributed hydrological models have contributed towards an improved realism of hydrological simulations. This advancement was supported by the broad range of readily available satellite-based datasets of key hydrological variables, such as evapotranspiration (ET). At larger scale, spatial patterns of ET are often characterized by an underlying climate gradient, and with this study, we argue that gradient dominated patterns may hamper the potential of spatial pattern-oriented evaluation frameworks. We hypothesize that the climate control of spatial patterns of ET overshadows the effect model parameters have on the simulated variability. To solve this limitation, we propose a climate normalization strategy. This is demonstrated for the Senegal River basin as modeling case study, where the dominant north-south precipitation gradient is the main driver of the observed hydrological variability. Two multi-objective calibration experiments investigate the effect of climate normalization. Both calibrations utilize observed discharge (Q) in combination with remote sensing ET data, where one is based on the original ET pattern and the other utilizes the normalized ET pattern. We identify parameter sets that balance the tradeoffs between the two independent observations and find that the calibration using the normalized ET pattern does not compromise the spatial patern performance of the original pattern. However, vice versa, this is not necessarily the case, since the calibration using the original ET pattern showed a poorer performance for the normalized pattern. Both calibrations reached comparable performance of Q. With this study, we identified a general shortcoming of spatial pattern-oriented model evaluations using ET in basins dominated by a climate gradient, but we argue that this also applies to other variables such as, soil moisture or land surface temperature.

Bioenergy Potential of Crop Residues in the Senegal River Basin: A Cropland–Energy–Water-Environment Nexus Approach

Access to energy services is a priority for sustainable economic development, especially in rural areas, where small- and medium-sized enterprises have many difficulties in accessing reliable and affordable electricity. Western African countries are highly dependent on biomass resources; therefore, understanding the potential of bioenergy from crop residues is crucial to designing effective land-management practices. The assessment of the capability to use crop residues for electricity production is particularly important in those regions where agriculture is the dominant productive sector and where electrification through grid extension might be challenging. The objective of this work was to guide the development of sustainable strategies for rural areas that support energy development by simultaneously favouring food self-sufficiency capacity and environmental benefits. These complex interlinkages have been jointly assessed in the Senegal river basin by an integrated optimization system using a cropland–energy–water-environment nexus approach. The use of the nexus approach, which integrates various environmental factors, is instrumental to identify optimal land-energy strategies and provide decision makers with greater knowledge of the potential multiple benefits while minimizing trade-offs of the new solutions such as those connected to farmers’ needs, local energy demand, and food and land aspects. By a context-specific analysis, we estimated that, in 2016, 7 million tons of crop residues were generated, resulting in an electricity potential of 4.4 million MWh/year. Several sustainable land-energy management strategies were explored and compared with the current management strategy. Our results indicate that bioenergy production from crop residues can increase with significant variability from 5% to +50% depending on the strategy constraints considered. An example analysis of alternative irrigation in the Guinea region clearly illustrates the existing conflict between water, energy, and food: strategies optimizing bioenergy achieved increases both for energy and food production (+6%) but at the expense of increasing water demand by a factor of nine. The same water demand increase can be used to boost food production (+10%) if a modest decrease in bioenergy production is accepted (−13%).