Evaluation and application of a portable rainfall simulator on subalpine grassland

Abstract

Abstract Rainfall simulators are commonly used instruments to study sheet erosion, since they can be set to predefined values like rainfall duration and quantity. The comparison between different irrigation studies is difficult, because general standards or methodological protocols do not exist for rainfall simulators. One goal of this study was to assess the suitability of a novel field hybrid rainfall simulator (FH simulator) that combines characteristics of a spray nozzle and a drop former rain simulator for erosion research. The FH simulator was compared to a larger scale laboratory drop former simulator (DF simulator) with a 7 m drop height by looking at the raindrop distribution, kinetic energy and the triggered runoff and sediment yield. Two soils with different textures were irrigated. A second goal of this study was to quantify the influence of vegetation and soil structure stability on soil erosion and runoff in a subalpine grassland area. Soil erosion and runoff reduction in relation to plant cover have been studied by numerous scientists in Mediterranean ecosystems, but researches in alpine grassland are spare. The kinetic energy, drop size, triggered runoff and sediment yield of both rain simulators were comparable, but kinetic energy and drop size differed for both simulators from natural rain. The clayish soil with stable soil structure and the silty soil with loose single grain structure differed significantly in runoff and sediment yield. Vegetation cover and sediment yield were correlated exponentially and soil structure stability improved significantly with increasing vegetation cover. Vegetation cover had no influence on surface runoff. These results demonstrate that vegetation cover plays a crucial role in alpine soils for soil structure stability and erosion. Even though it was not possible to achieve natural rain conditions with the used simulators, the proposed field simulator is a useful tool in steep alpine terrain to study relative differences in the effects of rain erosion on soils with differing characteristics and vegetation cover.