Effects of rainfall intensity fluctuations on infiltration and runoff: rainfall simulation on dryland soils, Fowlers Gap, Australia

Small plots and a dripper rainfall simulator were used to explore the significance of the intensity fluctuations (event profile) within simulated rainfall events on infiltration and runoff from bare, crusted dryland soils. Rainfall was applied at mean rain rates of 10?mm/h. Fourteen simulated rainfall events each involved more than 5000 changes of intensity and included multipeak events with a 25-mm/h peak of intensity early in the event or late in the event and an event that included a temporary cessation of rain. These are all event profiles commonly seen in natural rain but rarely addressed in rainfall simulation. A rectangular event profile of constant intensity, as commonly used in rainfall simulation experiments, was also adopted for comparative purposes. Results demonstrate that event profile exerts an important effect on infiltration and runoff for these soils and rainfall event profiles. Uniform events of unvarying intensity yielded the lowest total runoff, the lowest peak runoff rate and the lowest runoff ratio (0.13). These parameters increased for early peak profiles (runoff ratio 0.24) and reached maxima for late peak profiles (runoff ratio 0.50). Differences in runoff ratio and peak runoff rate between the uniform event profile and those of varying intensity were all statistically significant at p <= 0.01. Compared with uniform runs, the varying intensity runs yielded larger runoff ratios and peak runoff rates, exceeding those of the uniform events by 85%-570%. These results suggest that for small-plot studies of infiltration and erosion, the continued use of constant rainfall intensity simulations may be sacrificing important information and misrepresenting the mechanisms involved in runoff generation. The implications of these findings for the ecohydrology of the research site, an area of contour-aligned banded vegetation in which runoff and runon are of critical importance, are highlighted. Copyright (c) 2011 John Wiley & Sons, Ltd.