Enhancing rainfall simulator Efficiency: A search for new insights into performance parameters

Rainfall simulator (RS) is an indispensable tool for researchers conducting studies in hydrology, geomorphology, and erosion; however, performance evaluation varies due to differences in the methods used by each researcher. This study applies the concept of spatial variability within rainfall parameter limits and aims to contribute to a better calibration method for RS. Rainfall parameters such as intensity, homogeneity, and raindrop size were examined using different measurement strategies. A pressurized RS was tested in a controlled laboratory flume using nominal intensities of 40-, 70-, and 100-mmh-1 over a 2.4 m × 1.2 m (3.2 m2) test channel. The channel was divided into nine sub-areas, and the number and configuration of collection cups was varied above and below the channel using between 108 and 315 cups, with areal sampling densities of 16–48 %. Point rainfall intensities ranged from 15 to 185 mmh-1 within single events, depending on spatial position and cup configuration, which demonstrated that using a single representative parameter value will not allow for capturing the strong local variability that is present in RS. Christiansen Uniformity (CU) coefficients had clear regional disparities, with sub-area CU coefficients ranging between 66 and 96 %; under the best configuration, local CU coefficients reach 96 %, but lower density configurations had sub-area CU coefficient values as low as 66 %. With an increase in cup density, spread of measured intensities was reduced by more than one-third and produced smoother spatial patterns of uniformity while showing only minor corresponding shifts in CU values (typically on the order of ±1 % for a given nominal intensity). No systematic trend with cup number was displayed. The raindrop size characteristics only demonstrated a small but consistent increase in median raindrop diameter (D50) in response to increasing intensity, moving from 1.39 mm at 40 mmh-1 to approximately 1.60 mm at 100 mmh-1 with greater spatial variability being displayed at the higher intensity level. The results of this study emphasize the need for the incorporation of spatially sensitive calibration protocols for RS systems. The method outlined provides a more robust and comparable framework for evaluating rainfall simulator performance and thereby increases the reliability of simulation-based studies in environmental research.