Evaluating the impacts of land use and land cover changes on the spatial and temporal patterns of sediment connectivity: A case study of shallow landslides in the pre-Pyrenees of Catalonia

In hillslopes where landslides are the main mechanism of erosion, land use and land cover significantly influence sediment transfer downslope. This relation allows for assessing the spatial and temporal distribution of sediment flux within the basin.

An evaluation of the (dis)connectivity factors in the pre-Pyrenees region of Catalonia shows that the Saldes Basin has experienced a significant transformation in land cover over the past 30 years. There has been a notable 30% increase in shrublands and forests. This change is primarily attributed to the abandonment of agricultural practices in mountainous areas, allowing for a natural succession of vegetation.

This increase in forest cover usually results in reduced connectivity and lower erosion rates. However, soil erosion rates can rise significantly given the high risk of wildfires linked to these vegetation types. The destruction of vegetation and changes in soil properties can lead to increased runoff and sediment transport. Therefore, conducting a more detailed analysis of the relationship between sediment production and land cover is essential.

This project examines the relationship between soil erosion and land use and cover changes in mountainous areas. The methods and tools used in this study quantitatively analyze the current sediment production, the effects of vegetation, and the factors driving changes in land cover. This involves assessing geomorphometric parameters and hillslope processes and implementing an index of connectivity.

Integrating this analysis with an overland transport Monte Carlo model allows the assessment of the volume of sediment vulnerable to propagation. Based on climate change projections until 2100, the increase in overland transport to the targeted river is projected to rise by 2.8%, 9.6%, and 8.9% for the near, mid, and far future, respectively. This translates to a Landslide mobilization rate (LMR) of 75 to 500 tons per square kilometer per year reaching the target river, depending on different (dis)connectivity patterns.

The results aim to identify the source areas and understand sediment transport to the target river, facilitating a detailed investigation of sediment production within the basin. This evaluation helps to determine the potential of specific source areas to supply sediment to the main drainage system. The findings highlight critical areas that require intervention and enhance our understanding of how erosion processes vary spatially.