ON THE CONCEPT OF A REPRESENTATIVE ELEMENTARY AREA IN CATCHMENT RUNOFF

A qualitative discussion is presented on the concept of a representative elementary area (REA) proposed by Wood et al. (1988). Their work represents a systematic effort of looking at spatial variability as functions of scale, and over the past few years has stimulated new thoughts and research findings. However, it is argued here that the REA concept has limited utility in catchment hydrology for the following reasons. Firstly, the method of finding the REA using distributed modelling appears flawed. In estimating local runoff, point-process models are applied to elements of 30 x 30 m(2) or larger, but the effect of this particular upscaling on the calculated REA has not been addressed. This causes the REA to be relative to the resolution of the modelling. Secondly, an REA does not seem to exist in a natural environment because of its relativeness in the presence of multi-scale heterogeneity and its dependence on individual storm events. Based on the above arguments and following a discussion of the hydrological implications of REA, it is pointed out that the REA does not provide a definite and robust measure of the inherent spatial variability in runoff and that its utility in formulating large-scale hydrology is not as clear as it was first envisioned.