Experimental comparison of rainfall simulation methods for urban stormwater management research

Rainfall simulators are typically categorised as either pressurised or drop-forming systems, each offering distinct advantages depending on the research application. This study presents a comparative experimental analysis of a pressurised nozzle-based rainfall simulator and a drop-forming needle-based rainfall simulator, assessing their suitability for urban stormwater management research. Both setups were constructed indoors with a 1.5 × 1.5 m rainfall area and a 2.3 m raindrop fall height. The simulators were evaluated based on rainfall intensity, spatial uniformity, drop size distribution and drop velocity. The pressurised system produced intensities from 23.9 to 109.7 mm/h, while the drop-forming system achieved 4.5-21.0 mm/h. Uniformity coefficients ranged from 81.2 to 93.3% (cups) and 86.6 to 96.4% (trays) for the pressurised system, and 85.7% (cups) and 94.8% (trays) for the drop-forming system. D50 raindrop sizes ranged from 0.8 to 1.2 mm for the pressurised system and 1.7 mm for the drop-forming system. Estimated median drop velocities ranged from 82.5 to 98.5% of terminal velocity. While both systems replicated key rainfall characteristics, the pressurised simulator was limited to high-intensity events. The drop-forming simulator offered finer control and broader applicability, supporting its use in urban hydrology and stormwater management research.