Comparative Analysis of Compact Portable and Indoor Rainfall Simulators

Abstract. Rainfall simulators have been widely used and are indispensable in soil hydrology and erosion research. Although rainfall simulators can be used to address various research questions, there is no standardized methodology; they differ in design and rainfall characteristics. The present study aims to describe the design and testing of five rainfall simulator setups that vary notably in weight, volume, and transportability. Additionally, this article seeks to clarify procedural aspects involved in conducting a rainfall simulation in the field. The following parameters are used to compare the simulators: drop size distribution and terminal velocity, uniformity of the spatial distribution of raindrops over the sprinkled surface area (Christiansen uniformity coefficient; CU), kinetic energy (KE), and rainfall intensity. The Thies laser disdrometer and Tübingen Splash Cups (T-cups) were used to measure raindrop's KE to identify similarities and differences in their rainfall characteristics. The rainfall simulator setups produce rainfall intensities ranging from 28 to 95 mm h-1, with CU values ranging from 60.5% to 75.8%. More than 90% of measured drops were slower than 3.8 m s-1 for all simulations. The maximum number of drops was below 0.5 mm class, generally smaller than that observed in natural rain, and all at 1.4–1.8 m s-1 velocity. We found that kinetic energy (KE) measured with T-cups agreed with values calculated with the Thies disdrometer, confirming its relevance in rainfall studies. Indoor simulator setups produced the highest KEs, whereas the portable systems showed considerably lower values. This study emphasizes the importance of accurately characterizing rainfall parameters before soil erosion measurements. Rain simulators are then a powerful tool in erosion research. The presented methodologies and insights provide means for improved assessment of soil erosion risks, particularly regarding their practicality in remote areas.