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In this study, groundwater potential was mapped for a Mediterranean catchment using remote sensing techniques, geographical information systems (GIS), and the fuzzy analytical hierarchy (FAHP) process. Seven environmental factors were considered to influence groundwater potential, including soil type, lithology, precipitation, land use/cover, slope, lineament density, and drainage density. A FAHP method was implemented to calculate the weight of each factor and each class in the groundwater potential. The FAHP confusion matrix was established by eliciting opinions of local experts on factors that drive groundwater potential in this area. A weighted overlay was made in Arc-GIS™ for producing the final groundwater potential map. Three groundwater potential classes were considered (low, moderate, strong). Areas of very high potential represent 107.09 km2 (8%) of the total surface of the basin and are located in alluvial and calcareous formations of a high density of lineament and in areas with a low slope which promotes rapid infiltration. About 1022.124 km2 (71%) of the surface of the sub-catchment is characterized by a moderate to strong potential, while the remainder 305.945 km2 (21%) is characterized by a low potential. The results of the classification are validated by establishing the receiver operating characteristic (ROC) curve using 61 data from the wells located in the study area. The area under curve (AUC) yields 75.5% demonstrating the effectiveness of the method in identifying groundwater potential areas.

Sahelian woody vegetation has been the topic of many researches since the great drought that struck the Sahel in the 1970s-1980s. However, there is currently no consensus about the long-term trends of these savannas as observations sometimes seem contradictory according to the indicators used. Moreover, the observed trends often lack an understanding of the consequences on ecosystem functioning and subsequently on the provision of ecosystem services (ES), even if a decrease in ES is often assumed. As the inhabitants of the sylvo-pastoral zone of Senegal rely on these ES in their daily life, it is crucial to be able to predict the woody vegetation response to the current pressures acting on these ecosystems. In this research, we investigate the long-term trends of woody vegetation in order to discuss its persistence and its effects on two ecosystem functions (primary productivity and biogeochemical cycles) when facing three types of disturbances (drought, fire and grazing). This vegetation is examined from 1965 to 2018 using different indicators of the vegetation state and persistence, computed at several spatial scales and derived from multiple datasets (field inventory, remote sensing and literature). We first studied the spatial differentiation of the current woody vegetation according to the topography. Second, we evaluated changes since 1965 onward in terms of specific composition, density and woody cover. Third, we transposed the different indicators from the first two parts into a functional level of the woody communities, focusing on the vegetation response to pressure and effects on ecosystem. Based on this functional approach, we suggest some avenues for a potential management of this zone, in order to maintain the sylvo-pastoralism as land use. (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2020

Coral populations have declined dramatically worldwide under the combined effects of climate change and local anthropogenic stressors. In addition to ocean warming and acidification, threats to coral reefs in the Caribbean include frequent and virulent disease outbreaks, and intensifying hurricanes. In particular, Florida's Coral Reef (FCR) is currently facing a multi-year outbreak of the stony coral tissue loss disease (SCTLD). First observed in 2014 during the monitoring of the PortMiami Deep Dredge Project (PMDDP), the disease has now spread through the entire FCR and has been reported in numerous territories of the Caribbean. However, the propagation of the disease through FCR seemed to slow down when it reached its southwestern end, between the Marquesas and the Dry Tortugas (DRTO). Although the causative agent of the disease remains unknown, studies showed that its transmission was likely waterborne and that sediments could act as SCTLD vectors. The hydrodynamics should therefore be highly explanatory of its spread. Furthermore, Florida is a prime landfall target for hurricanes during the reproduction period of corals. In addition to causing wholesale destruction of the reefs, hurricanes might thus also impact larval dispersal through wind-wave-induced currents. Here, we use the high resolution coastal ocean model SLIM to capture transport processes in the FCR, and study the impact of SCTLD and hurricanes to coral reefs. First, a coupled epidemio-hydrodynamic model is developed to reproduce and understand the observed spread of SCTLD in Florida. A sediment transport model is then used to evaluate the impact of the PMDDP on the observed onset of the disease in 2014. Finally, a coupled wave-current model is implemented to study the impact of Hurricane Irma (2017) on transport processes over reefs in the Florida Keys. Assuming the dispersal of disease agents within neutrally buoyant material, our model successfully reproduced the observed spread of SCTLD through the FCR and linked its apparent stalling before reaching the DRTO to eddy activity in the Loop Current/Florida Current system. Furthermore, the results of our sediment transport model suggest that the PMDDP might have triggered the onset of the disease. Finally, our coupled wave-current model showed the important impact of wave-induced currents on transport processes over reefs during hurricanes. This thesis highlights the potential of models informed by and confronted against field knowledge as powerful tools to inform the management of complex marine ecosystems such as Florida's Coral Reef. (FSA - Sciences de l'ingénieur) -- UCL, 2022