Landslide mobilization rates: A global analysis and model

Landslides are a main driver of landscape evolution and a dominant sediment source in many regions worldwide. Nevertheless, their role in sediment mobilization and denudation remains poorly quantified, especially at the global scale. Based on an extensive literature review, we compiled measured contemporary landslide mobilization rates (i.e. the average annual volume of hillslope material displaced per unit area; LMR, [m(3)/km(2)/y]) from 116 study areas worldwide. Using this dataset, we calibrated and validated a multiple regression model that simulates global patterns of LMR at decadal timescales. This model explains about 62% of the observed variance in LMR based on topography, seismicity and lithology. By applying this model at the global scale and accounting for uncertainties due to observation and prediction errors, we estimate that annually about 56 billion m(3) (similar to 100 gigaton) is mobilized by landslides worldwide. Intercontinental and interregional differences are large with Asia accounting for 68% (38 billion m(3)) of the global LMR. The Central and Southeast Asian mountain ranges (including the Himalaya and Karakoram) account for 50% (28 billion m(3)) of this rate, while covering only 2% of the Earth's terrestrial surface. Comparisons of our simulated LMR with other data and models from literature suggest that, in highly tectonically active regions, around 70% of the mobilized landslide volumes are due to earthquake-triggered landslides. At the global scale, the contribution of coseismic landsliding to the total landslide mobilization rate is likely in the order of 30-40%. Using available databases of measured catchment sediment yield (SY), we also conducted a statistical comparison between measured SY and estimated LMR for nearly 3000 catchments in Europe and Africa. We observe highly significant relationships between LMR and SY for Europe (R-2: 0.35, p < 0.001) and Africa (R-2 : 0.2, p < 0.001). Furthermore, landslide mobilization rates are typically larger than the corresponding SY. Overall, this study provides a first estimation of the global patterns of LMR. The results confirm the importance of landsliding as a dominant process of landscape denudation and sediment mobilization, but also illustrate the huge regional variations that characterize this process as well as the importance of sediment dynamics within catchments.