Joris Eekhout

Assessing the impacts of environmental change on soil erosion and sediment yield at the large catchment scale remains one of the main challenges in soil erosion modelling studies. Here, we present a process-based soil erosion model, based on the integration of the Morgan–Morgan–Finney erosion model in a daily based hydrological model. The model overcomes many of the limitations of previous large-scale soil erosion models, as it includes a more complete representation of crucial processes like surface runoff generation, dynamic vegetation development, and sediment deposition, and runs at the catchment scale with a daily time step. This makes the model especially suited for the evaluation of the impacts of environmental change on soil erosion and sediment yield at regional scales and over decadal periods. The model was successfully applied in a large catchment in southeastern Spain. We demonstrate the model’s capacity to perform impact assessments of environmental change scenarios, specifically simulating the scenario impacts of intra- and inter-annual variations in climate, land management, and vegetation development on soil erosion and sediment yield.

Leaves are the major component of terrestrial litter input into aquatic systems. Leaves are distributed by the flow, accumulate in low flow areas, and form patches. In natural streams, stable leaf patches form around complex structures, such as large woody debris. Until now, little is known about flow conditions under which leaf patches persist. This study aims to quantify flow conditions for stable leaf patches and entrainment of leaf patches. We hypothesize that entraining flow processes, such as turbulence, Reynolds stress, or lift forcing (vertical flow velocity), best explain local leaf retention. This study was performed in an unscaled flume experiment, which conditions coincide with conditions found in low‐energetic lowland streams. We positioned a wooden obstacle perpendicular to the flow on the bed of the flume. A leaf patch was positioned downstream from the wooden obstacle. The experiment was performed under 5 flow conditions. We monitored leaf patch cover and near‐bed flow conditions in the area downstream of the wooden obstacle. We showed that near‐bed flow velocities explain leaf retention better than more complex flow velocity derivatives such as turbulence, Reynolds stress, and vertical flow velocity. The entrainment near‐bed flow velocity for leaves ranges from 0.037 to 0.050 m/s. Flow velocities frequently exceed those values, even in low‐energetic lowland streams. Therefore, complex structures, such as woody debris, create flow conditions to support stable leaf patches. Thus, adding instead of removing obstacles may be a key strategy in restoring biodiversity in deteriorated streams.

The parameterization of crop coefficients (kc) is critical for determining a water balance. We used satellite-based and literature-based methods to derive kc values for a distributed hydrologic model. We evaluated the impact of different kc parametrization methods on the water balance and simulated hydrologic response at the basin and sub-basin scale. The hydrological model SPHY was calibrated and validated for a period of 15 years for the upper Segura basin (~2500 km²) in Spain, which is characterized by a wide range of terrain, soil, and ecosystem conditions. The model was then applied, using six kc parameterization methods, to determine their spatial and temporal impacts on actual evapotranspiration, streamflow, and soil moisture. The parameterization methods used include: (i) Normalized Difference Vegetation Index (NDVI) observations from MODIS; (ii) seasonally-averaged NDVI patterns, cell-based and landuse-based; and (iii) literature-based tabular values per land use type. The analysis shows that the influence of different kc parametrization methods on basin-level streamflow is relatively small and constant throughout the year, but it has a bigger effect on seasonal evapotranspiration and soil moisture. In the autumn especially, deviations can go up to about 15% of monthly streamflow. At smaller, sub-basin scale, deviations from the NDVI-based reference run can be more than 30%. Overall, the study shows that modeling of future hydrological changes can be improved by using remote sensing information for the parameterization of crop coefficients.