Wind-Driven Rain as a new Challenge in Soil Erosion Research

• Applicant: Professor Dr. Johannes Bernhard Ries
• Subject Area: Physical Geography
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 254114232

Wind-driven rain - the great imponderable of soil erosion science. Soil erosion is now being recognised as one of the most severe environmental hazards threatening food security and environmental services. The effects of soil erosion are already raising socio-ecological issues of greatest concern for decision makers, and the situation is becoming even more severe with the ongoing climate change. But while great personnel and financial efforts are made to develop, parameterise and run numerical erosion models, the very basics of detachment and transport processes are far from understood. One of the great imponderables of soil erosion science is the influence of wind on raindrop, overland sheet flow and erosion of soil particles. Until now, the factor wind has widely been excluded from experimental investigations with rainfall simulations, partly because of the difficult development and setup of the needed experimental device. The few studies available indicate, that wind is an indispensable factor for the assessment of soil erosion on a global scale and the parameterisation of realistic soil erosion simulations. On different substrates, the surplus erosion generated by wind-driven rain ranged from +37.4% to +1108%, compared to windless rain erosion. The aims of the proposed study focus on this effect of wind on rain erosion. With the Portable Wind and Rainfall Simulator, that has been developed at Trier University, a new set of laboratory and field experiments will be designed and will highlight the influence of wind on rain erosion. It includes measurements and visual observation by means of a high-speed camera. Analysed processes are splash, splash-saltation (splash induced by wind-driven rain) and splash-drift (airborne and wind transported sediment during a wind-driven rain event) as well as wind-driven rain impacted and wind-accelerated overland sheet flow. The laboratory investigations on different types of standard substrates with varying wind velocities are complemented by field tests on autochthonous soil surfaces. The collected data from laboratory and field experiments are statistically analysed and key factors extracted. The camera observations are photogrammetrically processed. The data gained via different sets of experiments and ways of analysis, measured erosion data from laboratory and field tests, photogrammetrical evaluation of drop and particle movement and the statistically extracted key factors, are then gathered in a synthesis. The study is completed by the generation of a conceptual model to approach the wind-driven rain complex in a comprehensive way. This way, the proposed project achieves two superior objectives: - A goal-oriented basic research of the wind-driven rain dynamics to profoundly understand the analysed processes. - The generation of results urgently required for adequate erosion modelling.By combining complementary approaches, the effects of wind on rain erosion processes can be clarified.

• DFG Programme: Research Grants