Scale effects on plot runoff and soil erosion in a mediterranean environment

Abstract

Explaining scale effects for runoff and erosion improves our understanding of hydrological and erosion processes. In this investigation, plot-scale effects on event runoff per unit area, Qe, sediment concentration, Ce, and soil loss per unit area, SLe, were checked at the Sparacia (Italy) site. Similar information on the scale effects was obtained with different dependent variables, i.e., individual values of Qe, Ce, and SLe for each plot or the mean of their replicated values, and scale indicators, i.e., plot length, l, or plot area, A. The most common result, occurring for 57 to 62% of the events depending on the considered variable, was the lack of any scale effect. When scale effects were detected, they indicated that longer plot lengths yielded smaller Qe and SLe values and larger Ce values. Scale effects were more variable for erosion than runoff. Rainfall characteristics did not explain the occurrence of significant scale effects nor were they able to describe changes in the scaling exponent for Ce and SLe. However, there was some sign that scale effects for plot runoff decreased as rainfall amount or its erosivity increased. The collected data were not always sufficient to support the description of scale effects by the theoretically based power relationship. Additional investigations on plot-scale effects are advisable to both explain with more confidence what factors control the response of plots differing in length and establish the most appropriate way to summarize the data.