Testing the “physical model concept” by soil loss data measured in Sicily

The best possible model to predict the erosion from an area of land has been suggested to be a physical model of the area that has similar soil type, land use, size, shape, slope and erosive inputs. Therefore, a replicated plot has to be considered the best possible, unbiased, real world model. In this paper the physical model concept was tested by using soil loss data collected on plots of different length at the experimental station of Sparacia, in Sicily (South Italy). This investigation supported the conclusions that i) a coefficient of determination between measured and predicted soil loss values of 0.77 has to be considered as the best-case prediction scenario and ii) an uncalibrated deterministic erosion model would not give more accurate results than those obtained by a replicated plot measurement. An effectiveness coefficient of 0.47–0.49 was obtained by applying the original USLE to predict event soil losses at Sparacia. The difference between the value of 0.6, corresponding to what we can expect from an uncalibrated erosion model, and the effectiveness coefficient of the selected model represents the maximum gap that has to be covered to obtain the realistically best estimate of plot soil loss at the event temporal scale.

► The physical model concept allows to test reliability of soil loss model predictions. ► This concept, developed and only applied in U.S.A., was positively tested in Sicily. ► The coefficient of determination of measured vs. predicted soil losses was 0.77. ► A world data set should be developed to further test the physical model concept.