After long-term operation, a large-scale artificial rainfall simulation system can exhibit low automation, insufficient stability, and limited flexibility in rainfall intensity regulation. To address these deficiencies, a comprehensive optimization and performance evaluation was conducted to improve system reliability, controllability, and experimental applicability.

Three major subsystems were upgraded: (1) Power and control system: a high-precision stepper motor was installed, enabling fully continuous and automated regulation of rainfall intensity from 0 mm/h to 200 mm/h with 1 mm/h resolution. (2) Water supply system: a variable-frequency booster pump was integrated to maintain stable water pressure, and a mechanical float valve was added to automate water level control in the storage tank. (3) Hoisting system: manually operated pulleys were replaced with remote-controlled electric winches, and all power and water lines were consolidated within a flexible energy chain (cable carrier) to prevent abrasion and eliminate on-floor obstructions. An intelligent software module was also developed to enforce digital logging of user identity, experimental purpose, and funding source and to provide automated sampling reminders. Performance was evaluated through quantitative tests of rainfall intensity stability, spatial uniformity, raindrop size and velocity distributions (using a laser disdrometer), and operational efficiency.

Key improvements include the following: (1) The upgraded system yielded substantial gains in control precision, operational stability, and rainfall uniformity. By replacing the conventional electromagnetic clutch with high-precision stepper motors, rainfall intensity can be continuously and automatically regulated between 0 to 200 mm/h in 1 mm/h increments. The retrofitted water supply system, incorporating a variable-frequency booster pump and a mechanical float valve, ensures stable water pressure and steady delivery, guaranteeing reliable performance even under prolonged, high-intensity operation. Spatial uniformity coefficients measured 88.1%–89.7% at 2.5 m height and increased markedly to 93.5%–94.9% at 4.0 m, indicating excellent areal distribution. (2) Microphysical characterization revealed that raindrop mean diameters ranged from 0.86 to 1.03 mm, with volume median diameters (D₅₀) of 1.75–2.5 mm and maximum diameters of 4.5–5.5 mm across the tested intensities. In terms of number concentration, simulated raindrops were predominantly distributed between 0.125 and 5.5 mm, with most falling below 1.0 mm; only a negligible fraction exceeded this threshold. The joint frequency distribution of drop size and fall velocity showed the highest concentration in the 0.125–1.0 mm diameter and 1.0–4.0 m/s velocity ranges. Notably, the simulated drop size–velocity coupling matched observed torrential rain events particularly closely.

The optimized system reproduces the raindrop size distribution and combined diameter–velocity characteristics of natural rainfall, with the closest resemblance to storm-type precipitation. It therefore provides a reliable, controllable, and repeatable platform for experimental studies in soil erosion, hydrology, and allied disciplines. Nevertheless, given China’s vast territory and diverse climatic regimes, the microphysical properties of natural rainfall—including drop size spectra and velocity distributions—vary considerably across regions and synoptic weather types. While the present system demonstrates good correspondence with certain natural rainfall patterns, it does not fully replicate the entire spectrum of rainfall varieties encountered across the country. This limitation should be acknowledged when extrapolating experimental results to regions or rainfall types not directly represented by the current calibration database.