Abstract
BackgroundRainfall and other climatic agents are the main triggers of soil erosion in the Mediterranean region, where they have the potential to increase discharge and sediment transport and cause long-term changes in the river system. For the Magra River Basin (MRB), located in the upper Tyrrhenian coast of Italy, we estimated changes in net erosion as a function of the geographical characteristics of the basin, the seasonal distribution of precipitation, and the vegetation cover.Methods and findingsBased on rainfall erosivity and surface flow and transport sub-models, we developed a simplified model to assess basin-wide sediment yields on a monthly basis by upscaling the point rainfall input. Our calibration dataset of monthly data (Mg km-2 month-1, available for the years 1961 and 1963–1969) revealed that our model satisfactorily reproduces the net soil erosion in the study area (R2 = 0.81). For the period 1950–2020, the reconstruction of an annually aggregated time-series of monthly net erosion data (297 Mg km-2 yr-1 on average) indicated a moderate decline in sediment yield after 1999. This is part of a long-term downward trend, which highlights the role played by land-use changes and reforestation of the mountainous areas of the basin.ConclusionThis study shows the environmental history and dynamics of the basin, and thus the varying sensitivity of hydrological processes and their perturbations. Relying on a few climatic variables as reported from a single representative basin location, it provides an interpretation of empirically determined factors that shape active erosional landscapes. In particular, we showed that the most recent extreme storms associated with sediment yield have been characterised by lower cumulative rainfall, indicating a greater propensity for the basin to produce sediment more discontinuously over time.
Highlights
Understanding the long-term effects of hydrological variability and extremes [1,2,3] on the variability of soil erosion and sediment delivery is a challenge for environmental science [4]
This study shows the environmental history and dynamics of the basin, and the varying sensitivity of hydrological processes and their perturbations
In Italy, located in the centre of the Mediterranean region, where extreme rainfall events often appear elusive or in the form of small erratic clusters [6], agronomists and travellers have documented the timing of damaging hydrological phenomena and soil erosion already in historical times [7]
Summary
Understanding the long-term effects of hydrological variability and extremes [1,2,3] on the variability of soil erosion and sediment delivery is a challenge for environmental science [4]. [The mountains–Leonardo da Vinci had warned–are devastated by rains and rivers», and already Pietro de’ Crescenzi, a few centuries earlier, had recommended working across the hilly land, otherwise the land “would all be carried downstream when it descends strength from the slopes of the mountains”] Even after this period and up to present day, most Tuscan river basins have been strongly influenced by various types of climatic forcings and human disturbances, mainly from landuse changes related to agriculture, flood mitigation, and exploitation of natural resources [8,9,10]. For the Magra River Basin (MRB), located in the upper Tyrrhenian coast of Italy, we estimated changes in net erosion as a function of the geographical characteristics of the basin, the seasonal distribution of precipitation, and the vegetation cover
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