Simulating fluvial fluxes in the Danube watershed: The ‘Little Ice Age’ versus modern day

Climate change and human activities in Europe have altered erosion and riverine sediment transport for thousands of years. The Danube River basin, the second largest watershed in Europe, provides a unique study area to examine these impacts on fluvial discharge through available reconstructed climate data during the ‘Little Ice Age’ cold interval, as well as documented timing of deforestation and large dam emplacement. Suspended sediment flux of the Danube watershed and its variability in response to both climatic adjustments and human influences is analyzed at the sub-basin scale using a numerical modeling approach (HydroTrend 3.0). The system is examined over three time periods under conditions corresponding to: (1) modern day, (2) pre-dam and (3) the ‘Little Ice Age’. Modeled results indicate that modern-day suspended sediment flux is approximately 60% and 80% lower than that simulated under pre-dam and ‘Little Ice Age’ conditions, respectively. Disregarding the effects of modern-day dams, sediment flux has decreased 46% since the ‘Little Ice Age’, largely due to declining rates of deforestation since the mid to late twentieth century. High-resolution (decadal) analyses based solely on climate change, i.e. assuming no human impact, suggest that suspended sediment flux should be approximately 5% higher today than during the ‘Little Ice Age’, despite a 10% decrease in water discharge.This supports the view that human influence is the dominant forcing agent in modifying, and even reversing, natural processes on the Earth’s surface. Results also suggest that a 4°C increase in average European annual temperatures, as predicted by the Intergovernmental Panel on Climate Change for the end of this century, could result in increased sediment flux by 16–63% in individual basins.