Submitted to: First Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2003
Publication Date: 10/27/2003
Citation: Stone, J.J., Paige, G.B. 2003. Variable rainfall intensity rainfall simulator experiments on semi-arid rangelands. Proceedings First Interagency Conference on Research in the Watersheds, Oct. 27-30, 2003, Benson, AZ., pp.83-88. Interpretive Summary: Soil-vegetation groups are classified into Ecological Sites (ES) and used for rangeland evaluation and planning. How each ES responds hydrologically to changes in ecological condition has not be well quantified. This study examined how variable rainfall intensity as applied by a rainfall simulator influenced the rates of infiltration and the erosion process. The results indicate that at low to moderate rainfall intensities, runoff only occurs on parts of an area. Although the study did not identify which areas are contributing to runoff, there was a high correlation between the amount of bare area and occurrence of runoff. The results from the erosion data suggest that some of these bare areas called microterraces may be areas of significant deposition of detached sediment.
Technical Abstract: Most rainfall simulator experiments have used a constant rainfall intensity in their experimental design. However, when multiple intensities are used, the steady state infiltration rate tends to increase with increasing rainfall rate, indicating that runoff contributing area is a function of rainfall intensity. Hydrologic data from soil vegetation complexes (Ecological Sites) in Arizona and Mexico suggest that at typical rainfall simulator rainfall intensities, not all of the area is contributing to runoff with the effect being greater for coarse textured soils. Erosion data from similar Ecological Sites indicate that deposition can be a significant component of the total detachment on uniform slopes when microterraces are present. Variable intensity rainfall simulator experiments are necessary to understand and predict small scale hydrologic and erosion processes which may be important in evaluating the sustainability of rangeland hillslopes