AN APPROACH FOR SIMULATING RAINFALL ABOVE THE TREE CANOPY AT THE HILLSLOPE SCALE

Abstract

Rainfall simulation is a valuable experimental approach to study hydrologic and erosion processes. Most of therainfall simulation studies done on arid or semi-arid rangelands have been at the small-plot scale, and rarely with waterapplied above the tree canopy. A new methodology for simulating rainfall above tree canopies at the hillslope scale ispresented. The rainfall simulator that was developed consisted of modular components that are easily transported andinstalled at remote sites on rugged, brush-covered hillslopes. The simulator manifolds, which are equipped with four sprinklerheads, are supported by individual, telescoping masts that can be extended up to 11 m. The masts that support the manifoldsare mounted on base plates, designed to facilitate installation on steep hillslopes. the sprinkler-head manifolds are easilyinstalled on the masts using a quick-connect mounting bracket. The rainfall simulator is capable of simulating rainfall from25 to 250 mm/h at a height of 11 m. The rainfall simulator was field tested on a 7 14 m plot with the masts set at a heightof 5 m. For simulated rainfall rates of 25, 51, 76, 102, 127 and 153 mm/h, coefficients of uniformity ranged from 58% to 73%.Median raindrop diameters ranged from 1.7 to 2.4 mm, and associated kinetic energies varied from 16.8 to 25.9 J/m2-mm.The rainfall simulator has performed well with minimum maintenance and proved to be a cost-effective and efficient researchtool for replicating natural, above-canopy rainfall in arid and semiarid environments.