Topics for MSc theses at UNIL:

Exploring the feedback between landscape evolution and orographic rainfall

At geological timescales of millions of years, landscape evolution is influenced by tectonics and climate. Many studies have focused on the role of tectonics in shaping the landscape, but the role of climate, in particular rainfall magnitudes and patterns, has been relatively neglected. Rainfall does not stay stationary while a landscape evolves. It is theorized that there is a feedback mechanism between rainfall patterns and landscape evolution – the erosion of mountainous ridges reduces orographic rainfall, which in turn reduces erosion rates. In this thesis, a numerical rainfall model and a landscape evolution model will be used to analyze the feedback between orographic rainfall and erosion rates, as well as its impact on mountainous landscapes.

Intensification of extreme rainfall with warming

Increased temperatures lead to intensification of extreme rainfall. This phenomenon is explained by the Clausius–Clapeyron relation. According to recent studies, extreme rainfall intensification is caused by an increase in near-surface air temperature and sea surface temperature, but the relative contribution of each of these variables to the intensification of extreme rainfall is unclear. We will be able to reduce predictions’ uncertainty by understanding how each of these factors contributes to extreme rainfall intensification under climate change. Using variance statistical analysis, the effects of the two factors will be partitioned based on the data from climate reanalysis products.

Impacts of climate change on pre-Alpine catchments

Temperatures are expected to increase in Switzerland throughout the year while precipitation amounts will increase in the winter and decrease in the summer. This implies that catchments will have less water contribution from SWE (snow water equivalent), but that might be offset by the increase in rainfall. For this project, a numerical (physically-based) hydrological model will be used to predict the hydrological budget in the Emme catchment as a function of changing temperature and precipitation scenarios. Using different climate scenarios, the sensitivity of the catchment response to climate change can be determined and projected to other per-Alpine catchments.

Evaporation in urban areas and heavy summer rainfall

Evapotranspiration is suppressed by urban environments. This is due to several factors, including the reduced amount of vegetation compared to rural surroundings and the lower soil water content because of impervious surface within built-up areas, which reduces latent heat flux. As a result, rainfall amounts are expected to decrease in urban areas. In contrast, extreme summer rainfall is expected to intensify due to the urban heat island, which contributes to vertical convection and evaporation. It will have a direct impact on urban flooding. The urban evaporation excess during summer rainfall is a theory based primarily on climate models. Throughout this thesis, stable O and H isotopes will be used as a proxy to estimate the contribution of urban evaporation to heavy summer rainfall with the aim of verifying the theoretical framework of urban intensification of extreme rainfall events.