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Assessing hydropower flexibility for integrating solar and wind energy in West Africa using dynamic programming and sensitivity analysis. Illustration with the Akosombo reservoir, Ghana
No full textThe flexibility of hydropower plants with large reservoirs is frequently exploited to integrate large shares of variable and intermittent renewable energy sources in electricity systems. In this study, we assess the flexibility that could be provided by large hydropower reservoirs in West Africa to cope with planned future solar and wind energy generation in the region. Reservoir operations are estimated via Dynamic Programming with the objective to minimize the variability of the residual demand that commonly needs to be supplied by conventional generation means at high monetary and carbon costs. The analysis framework is demonstrated for the Akosombo hydropower reservoir in Ghana for which a number of future scenarios of increased electricity demand are considered. Different combinations of solar and wind energy development are considered to match the increase in demand. The results show that the Akosombo hydropower reservoir can smooth out the variability of the residual electricity demand when the increase in electricity demand is below 25% and the corresponding contribution of solar and wind energy to the total electricity generation does not exceed 20%. For larger increases in demand and thus larger solar and wind generation, the Akosombo reservoir cannot fully smooth-out the variability of the subsequent residual demand, although, the performance varies with the relative contribution of solar and wind in the energy mix. However, we found that the use of an additional short-term storage helps to further reduce the variability of the residual demand
Urbanisation and eutrophication as drivers of morphological and physiological divergence among riverine fish populations
No full textFreshwater ecosystems are highly impacted by human activities, but the effects of human-induced perturbations on fish phenotypic divergence remain poorly understood, especially in riverine systems. In this study, we tested the effects of urbanisation and eutrophication on several morphological and physiological traits in 17 gudgeon populations of Gobio occitaniae from South of France. We first demonstrated that eutrophication gradient was associated with changes in morphology and energy reserves, while urbanisation was associated with changes in body condition. More specifically, fish from highly eutrophic sites had deeper bodies and larger jaws, and a higher lipid content in their muscles. Urban fish had a higher body condition compared to their rural counterparts. The phenotypic divergence (P-st) among sites was significantly higher than the neutral genetic differentiation (F-st), suggesting that these morphological and physiological differences cannot be explained by neutral genetic drift alone. This study thus suggests that eutrophication and urbanisation are major drivers of phenotypic divergence in riverine fish populations, and calls for further experimental studies investigating the ecological and evolutionary effects of human activities on riverine fish populations
Fall armyworm, Spodoptera frugiperda (JE Smith) in maize cropping systems in Benin : abundance, damage, predatory ants and potential control
No full textInvasive fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a species native to the Americas which has spread to Africa in 2016. This insect has been reported in Benin as a major pest of maize causing important economic losses and putting at risk food and nutritional security. This study evaluated the damage caused by this pest to maize in different cropping system and management practices. It also assessed predatory ants presence and diversity and their potential in controlling FAW. Results showed that 50% of farmers grow maize in a mixed cropping systems in association with sorghum, cassava and cowpea and also used biopesticides. FAW larval population and damage in maize fields varied accros villages. Surprinsingly FAW larval population was higher in maize field sprayed with insecticides than untreated field. Seven species of predatory ants were recorded in maize field. Ants' population was higher in untreated field (1043 ants per hectare) than treated field (806 ants per hectare). In the laboratory, ants species exhibits great predatory potential. Further studies are needed to discuss uses of ants in FAW management in Benin
Deep ductile shear zone facilitates near-orthogonal strike-slip faulting in a thin brittle lithosphere
No full textSome active fault systems comprise near-orthogonal conjugate strike-slip faults, as highlighted by the 2019 Ridgecrest and the 2012 Indian Ocean earthquake sequences. In conventional Mohr-Coulomb failure theory, orthogonal faulting requires a zero frictional coefficient (pressure-insensitive), which is unlikely in the brittle lithosphere. The simulations developed here show that near-orthogonal faults can form in the brittle layer by inheriting the geometry of orthogonal shear zones nucleated in the deep ductile (pressure-insensitive) layer. In particular, if the brittle layer is sufficiently thinner than the ductile fault root, near-orthogonal faulting is preserved at the surface. The preservation is further facilitated by a depth-dependent strength in the brittle layer. Conversely, faults nucleated within the brittle layer are unlikely to form at orthogonal angles. Our model thus offers a possible explanation for orthogonal strike-slip faulting and reveals the significant interactions between the structure of faults in the brittle upper lithosphere and their deep ductile roots. Plain Language Summary Some notable earthquakes have occurred on sets of horizontally sliding vertical faults that cross each other at almost right angles (90 degrees). This is puzzling because the conventional theory of how Earth's brittle outer shell, the crust, breaks predicts a narrower angle between faults, close to 60 degrees. Our work offers an explanation to this puzzle. Theory also predicts that faults can form at right angles in rocks whose strength does not depend on the pressure acting on them. This is precisely the case in the deep viscous rocks that lie below the crust. Our computer simulations show that a pair of faults formed at right angle in deep viscous rocks can then grow upwards, gradually evolving to the narrower angle expected in the crust. If the crust is too thin, the faults reach the surface with almost right angles. Our proposed mechanism is effective on brittle crusts that are thinner than their viscous roots, which is the case in some regions where faulting at right angle is observed. Thus, our results show that the ductile root has important effects on the geometry of faults in the crust. Key Points . Simulations reveal shear bands in deep ductile layer induces orthogonal strike-slip faulting in thin brittle lithosphere Faults nucleated in brittle lithosphere are unlikely to form at orthogonal angles Low confining pressure at shallow depth facilitates near-orthogonal strike-slip faultin
Ship- and island-based atmospheric soundings from the 2020 EUREC(4)A field campaign [Data paper]
No full textTo advance the understanding of the interplay among clouds, convection, and circulation, and its role in climate change, the Elucidating the role of clouds-circulation coupling in climate campaign (EUREC(4)A) and Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) collected measurements in the western tropical Atlantic during January and February 2020. Upper-air radiosondes were launched regularly (usually 4-hourly) from a network consisting of the Barbados Cloud Observatory (BCO) and four ships within 6-16 degrees N, 51-60 degrees W. From 8 January to 19 February, a total of 811 radiosondes measured wind, temperature, and relative humidity. In addition to the ascent, the descent was recorded for 82% of the soundings. The soundings sampled changes in atmospheric pressure, winds, lifting condensation level, boundary layer depth, and vertical distribution of moisture associated with different ocean surface conditions, synoptic variability, and mesoscale convective organization. Raw (Level 0), quality-controlled 1 s (Level 1), and vertically gridded (Level 2) data in NetCDF format (Stephan et al., 2020) are available to the public at AERIS (https://doi.org/10.25326/137). The methods of data collection and post-processing for the radiosonde data set are described here
Intimate partner violence by men living with HIV in Cameroon : prevalence, associated factors and implications for HIV transmission risk (ANRS-12288 EVOLCAM)
No full textObjectives Intimate partner violence (IPV) against women is frequent in Central Africa and may be a HIV infection risk factor. More data on HIV-positive men (MLHIV) committing IPV are needed to develop perpetrator-focused IPV and HIV prevention interventions. We investigated the relationship between IPV and HIV transmission risk and IPV-associated factors. Methods We used data from the cross-sectional survey EVOLCam which was conducted in Cameroonian outpatient HIV structures in 2014. The study population comprised MLHIV declaring at least one sexual partner in the previous year. Using principal component analysis, we built three variables measuring, respectively, self-reported MLHIV-perpetrated psychological and physical IPV (PPV), severe physical IPV (SPV), and sexual IPV (SV). Ordinal logistic regressions helped investigate: i) the relationship between HIV transmission risk (defined as unstable aviremia and inconsistent condom use) and IPV variables, ii) factors associated with each IPV variable. Results PPV, SPV and SV were self-reported by 28, 15 and 11% of the 406 study participants, respectively. IPV perpetrators had a significantly higher risk of transmitting HIV than non-IPV perpetrators. Factors independently associated with IPV variables were: i) socio-demographic, economic and dyadic factors, including younger age (PPV and SPV), lower income (PPV), not being the household head (SPV and SV), living with a main partner (SPV), and having a younger main partner (SPV); ii) sexual behaviors, including >= 2 partners in the previous year (PPV and SPV), lifetime sex with another man (SPV), inconsistent condom use (SV), and >20 partners during lifetime (SV); iii) HIV-related stigma (PPV and SV). Conclusion IPV perpetrators had a higher risk of transmitting HIV and having lifetime and recent risky sexual behaviors. Perpetrating IPV was more frequent in those with socioeconomic vulnerability and self-perceived HIV-related stigma. These findings highlight the need for interventions to prevent IPV by MLHIV and related HIV transmission to their(s) partner(s)
Coastal protection assessment : a tradeoff between ecological, social, and economic issues
No full textMarine coastal ecosystems are crucial to human populations in reducing disaster risk. Least Developed Countries are particularly vulnerable to the effects of climate change, such as sea-level rise and storm surges. The Mauritanian coast, West Africa, ranks among the most vulnerable worldwide to sea-level rise, and coastal communities in the National Park of Banc d'Arguin (PNBA) are particularly at risk. Here, we assessed the service of coastal protection in PNBA by (1) mapping the coastal marine ecosystems with Sentinel-2 imagery and determining their spatial wave height attenuation rates; (2) assessing the vulnerability of villages and natural habitats to coastal hazard risk; and (3) assessing the applicability of coastal protection measures in the PNBA. We found that a total of 83% of the populated coastline presents a moderate to high risk of flooding and erosion, with Iwik and R'Gueiba being the most threatened villages in the PNBA. As for the ecological risk, two low-elevated islands, which support breeding colonies of birds, are particularly vulnerable to sea-level rise. However, in other areas, the rupture in the dune cord created new lagoons that present valuable ecological and economic interests like the Lagoon of Bellaat. Improving the comprehension of wave attenuation provided by coastal habitats, combined with identifying the vulnerability and applicability of coastal protection measures, is essential for achieving the Sendai Framework for Disaster Risk Reduction goals. In the PNBA, relocation of identified villages at risk is probably the best cost-effective solution with the least disturbance to both breeding and wintering birds. Protection of coastal ecosystems will also ensure a continued provision of other ecosystem services, including food supply for sea dependent populations, and contribute to achieving the Paris Agreement and Sustainable Development Goals
The X-TRACK/ALES multi-mission processing system : new advances in altimetry towards the coast
No full textIn the context of the ESA Climate Change Initiative project, a new coastal sea level altimetry product has been developed in order to support advances in coastal sea level variability studies. Measurements from Jason-1,2&3 missions have been retracked with the Adaptive Leading Edge Subwaveform (ALES) Retracker and then ingested in the X-TRACK software with the best possible set of altimetry corrections. These two coastal altimetry processing approaches, previously successfully validated and applied to coastal sea level research, are combined here for the first time in order to derive a 16-year-long (June 2002 to May 2018), high-resolution (20-Hz), along-track sea level dataset in six regions: Northeast Atlantic, Mediterranean Sea, West Africa, North Indian Ocean, Southeast Asia and Australia. The study demonstrates that this new coastal sea level product called X-TRACK/ALES is able to extend the spatial coverage of sea level altimetry data similar to 3.5 km in the land direction, when compared to the X-TRACK 1-Hz dataset. We also observe a large improvement in coastal sea level data availability from Jason-1 to Jason-3, with data at 3.6 km, 1.9 km and 0.9 km to the coast on average, for Jason-1, Jason-2 and Jason-3, respectively. When combining measurements from Jason-1 to Jason-3, we reach a distance of 1.2-4 km to the coast. When compared to tide gauge data, the accuracy of the new altimetry near-shore sea level estimations also improves. In terms of correlations with a large set of independent tide gauge observations selected in the six regions, we obtain an average value of 0.77. We also show that it is now possible to derive from the X-TRACK/ALES product an estimation of the ocean current variability up to 5 km to the coast. This new altimetry dataset, freely available, will provide a valuable contribution of altimetry in coastal marine research community
Temporal recovery of soil biological activity and diversity after 915-MHz microwave treatments
No full textTwo 915-MHz microwave treatments (2 kW-8 min and 4 kW-4 min) were applied to soil and their effects were monitored just after treatments (T0) and 26 days (T26) in soil microcosms. Densities of culturable bacteria, fluorescent pseudomonads and nematodes, hydrolysis activity and soil DNA content declined by over 50% immediately after both microwave treatments (T0), excluding the total fungal 18S rRNA (-13 or -17%) and bacterial 16S rRNA copies (non-significant). A rapid shift in bacterial community composition occurred from T0 towards a large increase in the relative abundance of Firmicutes (+1650%) and a concomitant decrease in various phyla (e.g. Acidobacteria, Actinobacteria, Bacteroidetes, Proteobacteria) from -85 to -61%. At T26 and for both treatments, fluorescein diacetate hydrolysis, density of culturable bacteria, 18S rRNA gene numbers, Simpson diversity, relative abundances of Bacteroidetes and Proteobacteria regained levels similar to controls. Alpha, Delta and Gamma classes Proteobacteria also end up reaching a similar level. In contrast, fluorescent pseudomonad density, nematode diversity and abundance, soil DNA content and relative abundances of some phylum (Acidobacteria, Actinobacteria, Chloroflexi) did not increase in such proportions. Most of the soil biological properties have not been permanently impacted. Nevertheless, the recovery kinetics highly differed according properties, with resilience indices at T26 varying from -87 to +99%