A stochastic sediment delivery model for a steep Mediterranean landscape

Abstract

It is a truism in geomorphology that climatic events operate on a landscape to drive sediment transport processes, yet few investigations have formally linked climate and terrain characteristics with geomorphological processes. In this study, we incorporate sediment transport equations derived from fieldwork into a computer model that predicts the delivery of sediment from hillslopes in a steep Mediterranean landscape near Santa Barbara, California. The sediment transport equations are driven by rainstorms and fires that are stochastically generated from probability distributions. The model is used to compare the rates and processes of sediment delivery under two vegetation types: coastal sage scrub and grasslands. Conversion of vegetation from sage to exotic grasses is a common land management strategy in the region and may also be engendered by regional climate change due to global warming. Results from the model suggest that (1) approximately 40% more sediment is delivered from grasslands (98 t km−2 yr−1) than the sage scrub (71 t km−2 yr−1) and (2) chronic soil creep processes dominate under grasslands whereas catastrophic processes dominate under coastal sage scrub. Results from the model also suggest that changes in the spatial distribution of vegetation arising from climate change will have a greater effect on sediment delivery than changes in the magnitude and frequency of meteorological events.