Evaluation of the impact of rainfall interception on soil erosion

Three research organizations, namely Faculty of Civil and Geodetic Engineering at the University of Ljubljana (UL FGG), Slovenian Forestry Institute (GI) and Technical University of Vienna (TUW) will jointly contribute to the proposed research project with their expertise in the field of rainfall interception and rainfall erosivity. The main aim of the project is the improvement of knowledge about rainfall interception by different vegetation and its impact on the rainfall erosivity based on high-frequency measurements at the already established experimental plots. Knowledge about this issue will be of paramount importance in the future, as due to climate change even more frequent and intense rainfall events with high erosive power can be expected. Investigation of rainfall partitioning is important both in natural environments as well as in urban areas. Urban trees reduce surface runoff, influence the evaporation and infiltration of water and may be due to the climate change more frequently used in the future as a part of green infrastructure. In natural environments rainfall interception and therewith rainfall erosivity is one of the most important parameters of the soil erosion with significant impact on the agricultural production and ecological conditions of the streams. Knowledge about sediment transport processes is relevant for controlling soil loss from agricultural land. Due to different types of vegetation, their unique characteristics and seasonality there are still a lot of open scientific questions. In order to achieve the main objectives of the project we will conduct extensive field measurements at three different experimental plots, namely two in an urban area of Ljubljana and one in an agricultural catchment in Austria. All three experimental plots will enable us to enhance the current research work and connect knowledge and experience of all three partners. At two locations in Ljubljana trees play important green infrastructure role. Currently, UL FGG is performing measurements in the urban park, where rainfall partitioning under individual trees of two different tree species is measured. On the other hand, GI is performing measurements in the urban mixed forest. In the frame of the project at both locations optical disdrometers will be used to measure drop size distribution (DSD) above and below tree canopies. Due to the fact that rainfall partitioning is influenced by numerous variables, we will simultaneously measure also several meteorological and vegetation parameters during different seasons. No measurements of rainfall interception have been performed so far at the catchment in Lower Austria. However, a substantial number of raingauges and a weather station are already part of the monitoring setup in the catchment. Furthermore, also intensive sediment monitoring is already in progress. In the scope of the project DSD measurements using optical disdrometers positioned above and below selected crops will be conducted in combination with classical measurements of rainfall partitioning. Based on the collected data and extensive analyses we will try to answer several open questions, such as what is the influence of different meteorological variables on rainfall and throughfall DSD in different climates, what is the influence of rainfall interception process on throughfall DSD below different types of vegetation (i.e. deciduous trees, coniferous trees, crops) in different seasons, what is the impact of the rainfall interception process on the erosive power of raindrops. Cooperation of experts of all three partners and comparison of the results of the analysis of high frequency measurements under different natural conditions related to climate, vegetation and soil is certainly an innovative research approach. Moreover, based on the project results we will prepare guidelines regarding the green infrastructure planning as well as soil erosion protection measures for relevant stakeholders.