A NEW RAINFALL SIMULATOR FOR USE IN LOW-ENERGY RAINFALL AREAS

Abstract

A sound assessment of hydrologic and erosional responses in wildland and agricultural ecosystems to rainfall requires that rainfall simulators mimic natural rainfall. The accuracy and usefulness of the assessment improves with increased similarity between natural and simulated rainfall. Some characteristics of natural rainfall important to rainfall simulation include rainfall energy, intensity, distribution, drop size distribution, time or season of application, and plot size. Our purpose for constructing a new rainfall simulator was to improve an old design with current technology. This equipment is especially needed for research in regions with low energy rainfall and convectional storms are not the primary source of excess rainfall and subsequent erosion. We developed a new rainfall simulator to simulate low energy rainfall under a wide range of ambient weather conditions. The simulator consists of four structures. Each structure simulates rainfall onto a 1.5 m wide ×9.1 m long plot, and consists of a frame for structural support and wind screening, three rotating disk-single nozzle modules, and control systems. The nozzle modules produce rainfall at five discrete intensities; 4.5, 9.0, 13.4, 17.9, and 35.8 mm/h. At the control center, water pressure at each nozzle is monitored and controlled to insure consistent rainfall over all treatments. Data loggers record water and air temperature in each structure during rainfall simulations. We tested uniformity of rainfall distribution and rainfall intensity. The coefficient of application uniformity for rainfall distribution within each structure is greater than 76, and rainfall intensity does not vary significantly (± 1 standard deviation) between structures. For our purposes, we developed this simulator for the evaluation of residue management, tillage methods, and farming systems. We used the simulator in subfreezing weather to evaluate residue management practices and concluded that the simulator is operable for data collection during all seasons and temperatures ranging from –5°C to 40°C. Rainfall simulation continues to be an important tool in efforts to understand how wildland ecosystems function and how agricultural practices might be improved. This rainfall simulator is an appropriate tool for hydrologic and erosion research in low energy rainfall regions.