The results of the energetic characterization of two drip-type rainfall simulators, differing in the length of their capillary tubes, are presented. The rainfall kinetic power and momentum were measured using a single capillary tube and applying weighing and photographic techniques to determine the raindrop mean equivalent diameter and fall velocity, respectively. The measurements highlighted that the simulated rainfall intensity is the only variable affecting raindrop diameter, and the increase in the capillary tube length produces a reduction in rainfall intensity and raindrop diameter. Finally, an empirical relationship relating fall velocity with raindrop falling height and diameter found in the literature was developed and positively tested using both the experimental data of the velocity measurements from the present research and the literature. Relationships to estimate the rainfall kinetic power and momentum based on the knowledge of mass and raindrop falling height were proposed and positively tested for the two simulators in the present investigation. In conclusion, operative guidelines for a drip-type simulator characterization are proposed in this paper, considering that the knowledge of the geometric characteristics of the capillary tube, pressure head, and falling height values are fundamental to having a complete energetic characterization of the rainfall simulator.

Research on water erosion often uses rainfall simulators, as these instruments allow for controlling the characteristics of the erosive agent and carrying out replications of experimental runs over brief time periods. In this paper, the early-step assessment of a new pressurized rainfall simulator equipped with nozzles differing in their spray angle and flow rate is developed. Experimental runs were performed to determine operative information about its functioning and rainfall intensity distribution. The investigated pressure–flow rate pairs, corresponding to values differing from those provided by the manufacturer, suggested that these nozzles are affected by their technological variability. Therefore, the use of the nozzles in pressure ranges that the producer did not investigate requires the testing of the manufacturer’s characteristic curves. The developed analysis on the variability of the measured average rainfall intensities and Christiansen’s Uniformity coefficient with the distance from the nozzle orifice demonstrates that the best simulation was obtained for the high-flow-rate nozzles at 120° and 90° with a pressure of 0.5 bar. These two simulation conditions allowed for the obtainment of rainfall intensities equal to 50 and 70 mm/h, respectively, and excellent uniform spatial distributions within a circular area with a diameter of 1.5 m. Moreover, to change the rainfall intensity during the simulation, the more effective approach was to maintain a constant pressure and modify the nozzle type, thereby modifying the nozzle spray angle. This finding underlines the importance of verifying the manufacturer’s nozzle characteristic curves and testing the rainfall intensity spatial distribution for selecting the nozzles most suitable for the simulation aims.

Rainfall kinetic energy is a critical variable in assessing rainfall erosivity, that is the capability of rainfall to erode soil. Accurate measurements of rainfall erosivity are essential for predicting soil loss and refining soil erosion models. Currently, rainfall energy is derived from measurements of raindrop size distribution (DSD) and raindrop terminal velocity. However, traditional disdrometers, which measure DSD, face limitations related to both the produced large datasets and the high costs associated with their deployment, especially over large areas, limiting their use to experimental installations for scientific research. Recent advancements have introduced a patented method to measure rainfall energy, relying on the simultaneous detection of rainfall intensity and the number of raindrops impacting a surface within a specific time interval. This paper presents advances in the theoretical measurement method of rainfall kinetic power and momentum by using Weibull distribution and rainfall momentum distribution. The developed theoretical analysis aimed at enhancing the reliability of this innovative approach for measuring rainfall kinetic power and momentum, by the detection of the rainfall intensity, number of the raindrops and the mean raindrop diameter calculated by the raindrop momentum distribution. This analysis developed by using measured DSDs demonstrates that the proposed approach provides accurate estimates of rainfall kinetic power and momentum, but also of the shape and the scale parameters of the DSD. Furthermore, the results suggest that the momentum distribution-based estimates of rainfall momentum are more accurate than those of kinetic power, due its reduced sensitivity to uncertainties in terminal velocity calculations. Implementing direct measurements of rainfall erosivity, this method could significantly improve the accuracy of erosion models and contribute to more effective large-scale monitoring of soil erosion risk.

Rainfall simulators are crucial devices in erosion research, enabling the controlled reproduction of precipitation characteristics for both laboratory and field investigations. This study presents a comprehensive characterization of a rainfall simulator originally designed to assess the erosive effects of precipitation on heritage surfaces. The simulator, installed at the University of León, was evaluated using volumetric methods and disdrometric techniques, employing a Parsivel² optical disdrometer. Simulations were conducted with a falling height of 10 m and high-intensity rainfalls. Spatial uniformity was assessed through thematic mapping and the Christiansen Uniformity (CU) coefficient, revealing limited uniformity across the full wetted area, but an improved performance within the central zone (CU up to 80%). Disdrometric data provided detailed insights into drop size and velocity distributions, enabling the estimation of rainfall intensity, kinetic energy, and momentum, as well as the spatial uniformity of the energetic parameters. Empirical models to estimate the raindrop’s fall velocity were tested against disdrometric measurements, confirming the simulator’s ability to generate rainfall with velocity characteristics comparable to those of natural precipitation. Moreover, the findings underscore the importance of integrating multiple measurement approaches to enhance the reliability and accuracy of rainfall simulator characterization.