A framework for modelling emergent sediment loss in the Ombrone River Basin, central Italy

Water can represent a hazard causing soil erosion and it is essential to anticipate the potential environmental impacts of sustained rainwater energy to achieve sustainability. Here, we present the modelling of the erosive force of water for the production of soil sediment in a Mediterranean basin of central Italy (Ombrone River Basin, ORB). A point of departure is the historical recognition of the environmental factors causing sediments loss (SL) by water. A semi-empirical framework was then proposed for the upscaling of SL based on the Foster-Thornes approach (EUSEM: Environmental Upscaling Sediment Erosion Model) in order to give an insight into annual sediment losses (SL) over the period 1949–1977 (calibration) and over a longer time-frame (1942–2020: reconstruction). Two change-points were detected: 1967 and 1986. During this period, SL was affected by a sharp decrease from 625 Mg km-2yr-1, before the first change-point (when SL was only occasionally below the tolerable soil loss threshold of 150 Mg km-2yr-1), to 233 Mg km-2yr-1, during the transition phase 1967–1985 (mostly above the warning treshold of 140 Mg km-2yr-1). This decrease coincided with an enhancing of vegetation throughout the basin due to an ongoing afforestation process. After this period, a resurgence of climatic forcing led to a further, but more contained, increase in SL, from 1996 onwards. This case-study illustrates the application and results that can be obtained with the framework for the outcome of environmental change due to sediment losses in a Mediterranean fluvial basin. Limitations and perspectives of this approach are given as conclusion.