Climate or land cover variations: what is driving observed changes in river peak flows? A data-based attribution study
Climate change and land cover changes are influencing the hydrological regime of rivers worldwide. In Flanders (Belgium), the intensification of the hydrological cycle caused by climate change is projected to cause more flooding in winters, and land use and land cover changes could amplify these effects by, for example, making runoff on paved surfaces faster. The relative importance of both drivers, however, is still uncertain, and interaction effects between both drivers are not yet well understood. In order to better understand the hydrological impact of climate variations and land cover changes, including their interaction effects, we fitted a statistical model for historical data over 3 decades for 29 catchments in Flanders. The model is able to explain 60 % of the changes in river peak flows over time. It was found that catchment characteristics explain up to 18 % of changes in river peak flows, 6 % of changes in climate variability and 8 % of land cover changes. Steep catchments and catchments with a high proportion of loamic soils are subject to higher peak flows, and an increase in urban area of 1 % might cause increases in river peak flows up to 5 %. Interactions between catchment characteristics, climate variations and land cover changes explain up to 32 % of the peak-flow changes, where flat catchments with a low loamic soil content are more sensitive to land cover changes with respect to peak-flow anomalies. This shows the importance of including such interaction terms in data-based attribution studies.