Quantifying the effects of rainfall temporal variability on landscape evolution processes

Lausanne, Quartier Centre, CH-1015 Lausanne, Switzerland Rainfall characteristics such as its intensity, duration, and frequency are key determinants of the hydro-geomorphological response of a catchment. The presence of non-linear and threshold effects makes the relationship between rainfall variability and geomorphological dynamics difficult to quantify. This is particularly relevant under predicted exacerbated erosion induced by an intensification of hydroclimatic extremes. In this study, we quantify the effects of changes in rainfall temporal variability on catchment morphology and sediment transport across a broad spectrum of grain size distributions and climatic conditions. To this purpose, multiple rainfall realizations are simulated using a rainfall generator, while geomorphic response and soil erosion dynamics are assessed by means of a landscape evolution model (CAESAR-Lisflood). A virtual catchment is used for the numerical experiments and simulations are run over centennial time scales. Preliminary results show that higher rainfall temporal variability increases the net sediment discharge as well as the domain erosion and deposition volume, with dry regions responding more actively to temporal rainfall variations and finer grain size configurations amplifying the observed response. Side channels developed longer and more in deeper in response to higher precipitation temporal variability. Such a quantification of the effects of predicted changes in rainfall patterns on catchment hydro-geomorphic response, as mediated by local soil properties, is crucial to forecast future changes in sediment and soil carbon fluxes.