Xing, Fei 1 ; Kettner, Albert J. 2 ; Hannon, Mark T. 3
1 CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder
2 CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder
3 CSDMS Integration Facility, INSTAAR, University of Colorado, Boulder
The Ebro Delta, one of the largest wetland areas (320 km²) in the western Mediterranean region, has undergone a series of complicated stages since its formation about 6000 years ago, due to changes in climate and human impacts. For example, an intensification of precipitation leads often to an increase in fluvial sediment load that gets transported to a deltaic area and visa versa. The Ebro Delta is no exception in this as climate varied over the last 2000 years. On the other hand, human impact on the drainage basin started as early as the Roman times by deforestation of large areas. Most likely this human interference in the form of deforestation increased the delta progression rate as well, that together with changes in climate led to the current shape of the Ebro Delta (Canicio, A. and Ibanez, C., 1999). In the last 50 to 60 years dams and reservoir construction for energy and irrigation purposes, are trapping more than 99% of fluvial sediment (Tena et al., 2010), which might result in the recession of the Ebro delta in the nearby future.
In order to explore the extent of climate change and human impact on the evolution of the delta, two models were applied to simulate the Ebro Basin and delta for the last 2000 years. HydroTrend, a climate-driven hydrological transport model is used to reproduce the freshwater and sediment flux to the delta, and subsequently a coastline evolution model (CEM) is applied to simulate the according changes in delta and coastal line morphology. A model-coupling tool CMT, is used to join the two models for this study. Validation of the HydroTrend model for the last 50 years indicates that the hydrological model is able to mimic the observed water discharge and sediment loads. Confident that the hydrological model can reproduce the water and sediment flux to the deltaic area, historical climate data and human impact information is applied to simulate the fluvial signal to the delta for the last 2000 years. Preliminary results indicate that given our model input assumptions, the sediment flux to the ocean follows the trend of climate change, but is increasingly influenced by human interference over time, by an order of magnitude. Human interference is first noticeable by devastating deforestation rates that significantly increased the sediment flux to the deltaic area and thereafter by the construction of dams and reservoirs that consequently let to a dramatic decrease of sediment flux to the ocean (Fig.1). At the same time, climate sensitive analysis shows that river discharge is defined by precipitation, while the sediment flux seems to express a larger correlation with temperature change, however humans due have the most significant impact on changes in sediment flux.
Tena,A., Batalla,R.J.,Vericat,D.,López-Tarazón,J.A.,2010. Suspended sediment dynamics in a large regulated river over a 10-year period (the lower Ebro, NE Iberian Peninsula): Geomorphology, v.125,p.73-84.
Canicio,A.and Ibanez,C.,1999.The Holocene Evolution of the Ebro Delta,Catalonia,Spain:Acta Geographica Sinica,v.54,p.462-469.