Applicability of Uncertainty analysis to groundwater environmental risks through Fault Tree Analysis and Monte Carlo simulations

The Anthropocene epoch initiated by human influence on its Earth system (atmosphere, biosphere, hydrosphere) leads to an irreversible change: Global Warming. Since climate change would increase the occurence's probability of undesired events (sea level rise, floods, extreme droughts, etc...), it leads to the concept of environmental risk which refers in its most basic definition as the combination of the consequences of an undesired event (Vulnerability) and its probability of occurrence (Hazard). As a consequence, it is necessary to study this alteration of existing natural processes, including the ones related to hydrogeology, in a probabilistic maneer.
This thesis aims to study the occurrence's probability of two particular groundwater risks. The first one is related to the generation of thermokarst lakes in permafrost environment and its subsequent thermal consequences in the surroundings. The second one concerns seawater intrusion which can induce saltwater contamination in abstracting wells. These processes are dependent of physical parameters to which is attached uncertainty. As a consequence, two uncertainty analysis methods have been applied to determine the failure's probability of these undesired events: Fault Tree Analysis and Monte Carlo Simulation.
Beside the rough approximation performed to evaluate the probability of thermokarst lake generation (48%) and of talik development under these latter (73%) by means of Fault Tree Analysis, these high failure probabilities translate the urge to restrain Global Warming due to its irreversible effects on permafrost environment. These include the thawing of the permafrost and the consequent releasing of its trapped methane into the atmosphere. On the other hand, Monte Carlo simulations have been performed to compare different scenarii related to seawater intrusion in Akrotiri aquifer in Cyprus. The results once again translate the disastrous effect of climate change regarding the probability of occurence of these unwanted events. Indeed, a failure probability around 6 times greater (43%) is observed in the climate change scenario with respect to the reference scenario (7%).
Uncertainty analysis is a good methodology to apply to environmental concerns to quantify the occurence's probability of these undesired events. This would urge public authorities to perform decision making in order to avoid or reduce the failure's probability of these groundwater issues that have irreversible consequences on its surrounding environment.