A new global database of 86 deltas and river basins was analyzed to investigate the relative importance of deforestation and land use changes versus natural forcings in determining long-term total delta size. Results show that mean river flow and shelf slope were the most important variables, whereas population density and sediment load had a much lower importance. Deforestation and other variables related to land-use generally had a very small effect, but were more influential in a subset comprising Mediterranean and Black Sea deltas. As most deltas have developed over thousands of years, the much shorter-lived anthropogenic signals from deforestation and other landscape perturbations have had only secondary impact on the total area of deltas. Also, delta progradation is strongly influenced on sand deposition, whereas anthropogenic impacts on sediment load have more often impacted mostly the finer sediment being deposited offshore (prodelta deposits) or in the deltaic plain. These data disproves the hypothesis that delta size and growth is strongly influenced by human forcings, particularly for larger deltas, since Holocene delta building is mainly determined by natural forces. However, humans are influencing the geomorphology of deltas, particularly over the last century when the Anthropocene nature of deltas has become manifest. A more precise terminology is proposed to clarify concepts such as “human-made”, “human-engineered” or “human-influenced” deltas.
Dr. Carles Ibáñez is Senior Researcher at the Department of Marine & Continental Waters of IRTA and former Head of the Department of Aquatic Ecosystems in the period 2005-2017. PhD in Biology from the University of Barcelona and post-doc in the Laboratory of Fluvial System Ecology of CNRS (France). He has 30 years of research experience in the field of aquatic, coastal and wetland ecology, sustainable management of water resources and environmental management, with more than 80 papers published in peer-reviewed international journals. He has been member of the Advisory Council of Sustainable Use of Water of the Government of Catalonia, and is currently member of the Advisory Council for Sustainable Development of the same government. He is also member of the Group of Experts on Climate Change of Catalonia, as well as of the Global Research Alliance on Agricultural Greenhouse Gases. Expert reviewer of the Fifth IPCC Report on Climate Change 2013: Impacts, Adaptation and Vulnerability (Working Group II). Associated Editor of the Journal Estuaries & Coasts.
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