Climate change and sediment dynamics in the central Mediterranean: a multi-scale assessment of riverine transport decline and coastal erosion

Fluvial sediment transport plays a fundamental role in shaping fluvial and coastal systems in the central Mediterranean, contributing to the formation of floodplains and deltas and to the maintenance of sandy coastal equilibrium. Over recent decades, this balance has been progressively altered by climate change, which has significantly modified precipitation regimes, their seasonality, and the intensity of extreme events, with direct effects on hydrological and sedimentary dynamics along the entire fluvial–coastal continuum.

This study investigates a century of sediment dynamics in Italy by analysing historical fluvial sediment transport data using modern machine learning techniques. Analyses conducted on the Arno and Ombrone rivers (central Italy) reveal a marked decline in suspended sediment transport since the 1930s. Model results indicate that climate change represents the primary controlling factor of this trend, mainly through reduced precipitation, rising temperatures, and the reorganization of atmospheric circulation patterns. Anthropogenic pressures, such as dam construction and land-use changes, contribute to the observed signal but are overall less influential than climate-related factors.

In addition to the long-term analysis, the study also includes the sampling and analysis of recent fluvial sediment transport data. Although these results are still preliminary, they highlight a level of complexity in sediment transport dynamics that cannot be explained solely by the geographical or morphometric characteristics of river basins. The interaction between climatic forcing, antecedent hydrological conditions, and intense precipitation events emerges as a key control on sediment fluxes, pointing to the need for more integrated and dynamic interpretative approaches.

At the national scale, shoreline evolution was analysed along 3,624 km of sandy coasts (1984–2024) using Landsat imagery and the CoastSat algorithm. The results indicate that 66% of major Italian rivers are associated with eroding coastal sectors; this percentage increases further, exceeding 75% when considering river deltas, which exhibit erosion on at least one of the two delta flanks, and reaches 100% along coastal stretches lacking artificial defence structures.

Overall, Italian river deltas emerge as among the most vulnerable areas in the Mediterranean under ongoing climate change. These findings underscore that only integrated strategies linking continuous monitoring, data infrastructure, and spatial planning can ensure sustainable sediment management and enhance coastal system resilience in a changing climate.