Climate change is modifying global precipitation patterns and bringing about unprecedented changes in the different facets of the water cycle. In order to be better prepared for the potentially adverse impacts of climate change on water resources, we need to improve our understanding of the water cycle. Environmental tracers such as stable water isotopes provide a useful medium to help untangle the complex web of Earth System processes. Stable water isotopes are naturally present in rainfall and snowfall, making them an ideal environmental tracer to track the journey of a water particle along its entire hydrologic life cycle.
In this thesis, I use stable water isotopes to improve the representation of hydrological processes occurring within mountainous landscapes in rainfall-runoff models. In the first chapter, I undertake a comprehensive review of ways in which stable water isotopes have been used in snow hydrology, with a special focus on mountainous environments. This review explains the different transformations that a water particle undergoes once it enters the landscape through rainfall or snowfall. In the second chapter, I build a novel Bayesian mixing model that derives valuable information from stable water isotope data, while taking into account the numerous limitations of field hydrology. In the third chapter, I propose a new hydrologic modeling framework that uses information derived from stable water isotopes, as illustrated in Chapter 2, to build more reliable rainfall-runoff models by constraining both the celerity and velocity behavior of catchments. This modeling framework is comprehensively evaluated in a Swiss Alpine catchment called Vallon de Nant. Finally, in the fourth chapter, I use stable water isotopes, streamflow recession analysis, and a conceptual groundwater model to show how climate change may increase groundwater recharge in the Swiss Alps.
This thesis therefore improves our understanding of the dominant hydrologic processes occurring in mountainous environments, and provides a novel approach to parameterize these processes within rainfall-runoff models. The key findings are summarized in the final chapter, where I also highlight practical challenges in isotope hydrology, and propose future research directions.