A portable integrated rainfall and overland flow simulator T. Alves S obrinho 1 , H. G o ´mez -M acpherson 2 & J. A. G o ´mez 2 1 Federal University of Mato Grosso do Sul, 79070-900, Campo Grande, MS, Brazil, and 2 IAS-CSIC, Alameda del Obispo, Apartado 4084, 14080 Co ´rdoba, Spain Abstract This paper describes a prototype of a portable rainfall simulator that can simulate a wide range of rainfall intensities with a kinetic energy similar to that of natural rainfall and, more innovatively, pro- vide simultaneous or independent simulations of rainfall and overland flow at the microplot scale (0.70 m 2 ). The design of the rotating shutter disc makes possible a wide range of rainfall intensities, from 30 to 155 mm ⁄ h without changing nozzle type or working pressure. Overland flow intensity can be adjusted from 94 to 573 mm ⁄ h depending on nozzle type and working pressure. The flow is applied on the upper side of the experimental plot. The Christiansen coefficient of uniformity of the simulated rainfall varied between 81.4 and 85.1%, and the calculated kinetic energy was >90% the kinetic energy of corresponding natural rain. Special attention was paid to portability. Stainless steel was used whenever possible and the equipment was constructed in modules so that it could easily be dismantled and carried by two people. A telescopic-type frame allows operation on sloping ground. Keywords: Rainfall simulator, overland flow, infiltration, erosion Introduction Rainfall simulators are used in studies ranging from determi- nation of soil characteristics, such as water infiltration rate or surface storage, to specific erosion processes. They are especially valuable in studies aimed at characterizing the effect of different soil management types on soil properties (e.g. Go´mez et al., 1999) or at calibrating hydrological and erosion models (e.g. Connolly et al., 1991). There are several reasons to use simulated rainfall. One is that it reduces the time and costs required for experimentation as experiments based on natural rainfall require a long period of monitor- ing. In addition, simulated rainfall allows better control of the experimental conditions and the possibility of repeating experiments under identical conditions, something which is not possible with natural rainfall. There are several published reviews on rainfall simulators that cover in detail their evolution since the 1930s and their different designs (Peterson & Bubenzer, 1986; Cerda`, 1999). Several key parameters need to be considered in their design, e.g. impact velocity, drop size distribution and rainfall inten- sity, and these should be chosen depending on the aim of the study. Ideally, the rainfall simulator should be able to repro- duce the average drop diameter, terminal drop velocity and the kinetic energy of natural rainfall. It is also important to simulate a wide range of intensities while maintaining the characteristics of the rainfall and its uniformity of applica- tion. The final design of a rainfall simulator is a compromise between these requirements, portability and ease of use in the field. The more important limitations are the restricted area over which rainfall can be simulated, the inability to completely match the characteristics of natural rainfall events, and the logistical difficulties of carrying out the simu- lations when and where necessary. These are some of the rea- sons that highlight the need for complementary studies using simulated and natural rainfall. The use of rainfall simulators is necessarily limited to small working areas. Approximately 50% of the 229 simula- tors described by Cerda` (1999) simulate rainfall over areas <1.5 m 2 . Rainfall simulations on areas of 0.75–1.5 m 2 have been used to study soil properties, surface sealing and inter- rill and splash erosion (Farres, 1987; Connolly et al., 1991; Mohanty & Singh, 1996; Morin & Van Winkel, 1996; Go´mez et al., 1999). However, these simulators cannot be used for studying processes that are scale dependent, e.g. rill erosion as they require larger areas (e.g. Go´mez & Nearing, 2005). Another shortcoming is the impossibility of achieving large overland flow depth and shear stress as required in studies of pesticide transport or detachment transport of soil mulch. For these types of studies, an overland flow simulator such as the one described by Wolfe et al. (2000) is required. We Correspondence: T. Alves Sobrinho. E-mail: talves@nin.ufms.br Received August 2007; accepted after revision December 2007 Soil Use and Management, June 2008, 24, 163–170 doi: 10.1111/j.1475-2743.2008.00150.x ª 2008 The Authors. Journal compilation ª 2008 British Society of Soil Science 163