Disentangling Plant-Induced Soil Effects on Runoff: Experiments and Modeling of Miscanthus

Land use is a key driver of differences in runoff generation and play an important role in water retention and the mitigation of surface runoff during high-intensity rainfall events. Perennial crops’ permanent root system and persistent mulch layers can substantially modify soil physical properties in comparison to annual crops, thereby influencing soil hydraulic functioning and runoff generation processes. While existing studies commonly compare the effects of perennial crops on infiltration, runoff, or water balance at longer temporal scales, experimental data on runoff responses under short, high-intensity rainfall events are quite scarce. In particular the hydrological behavior of agricultural fields cultivated with perennial crops remains poorly understood. For Miscanthus x giganteus, a perennial crop commonly grown for bioenergy production and increasingly investigated as a sustainable building material, observations on hillslopes in the Erft catchment during heavy rainfall events in 2016 and 2022 suggest runoff retention effects. Therefore, we quantified the influence of Miscanthus on runoff generation during heavy rainfall events. A series of different artificial rainfall experiments were conducted on three different 10 x 10 m plots cultivated with Miscanthus, winter wheat and permanent pasture serving as reference land-use type. Surface and subsurface runoff were measured at the bottom of each hillslope plot under different rainfall intensities producing in total 36 experiments. To separate the plant-induced effects on soil structure and hydrological processes, the experiments were also simulated with the process-based runoff-generation model RoGeR, which includes various preferential flow processes. The results from the measurements indicate a pronounced retention effect of Miscanthus during the runoff initiation phase, leading to lower runoff rates than winter wheat. However, no clear differences in total surface runoff volumes were observed under the applied rainfall conditions. These findings indicate that the persistent mulch layer associated with perennial crops such as Miscanthus can substantially modify runoff dynamics during high-intensity rainfall events and reduce soil erosion. Ongoing modelling of the experiments with RoGeR aims to quantify the contribution of different preferential flow paths and to investigate why Miscanthus does not reduce total surface runoff relative to tall, fully developed winter wheat. The results will improve process-level understanding of the effects of perennial crops on runoff generation under extreme rainfall events and have implications for the assessment of nature-based solutions and land-management strategies aimed at flood mitigation.