Abstract
Abstract. The diverse sources of uncertainty associated with the calculation of rainfall kinetic energy and rainfall erosivity, calculated from precipitation data, were investigated at a range of temporal and spatial scales in a mountainous river basin (504 km2) in the south-eastern Pyrenees. The sources of uncertainty analysed included both methodological and local sources of uncertainty and were (i) tipping-bucket rainfall gauge instrumental errors, (ii) the efficiency of the customary equation used to derive rainfall kinetic energy from intensity, (iii) the efficiency of the regressions obtained between daily precipitation and rainfall erosivity, (iv) the temporal variability of annual rainfall erosivity values, and the spatial variability of (v) annual rainfall erosivity values and (vi) long-term erosivity values. The differentiation between systematic (accuracy) and random (precision) errors was taken into account in diverse steps of the analysis. The results showed that the uncertainty associated with the calculation of rainfall kinetic energy from rainfall intensity at the event and station scales was as high as 30%, because of insufficient information on rainfall drop size distribution. This methodological limitation must be taken into account for experimental or modelling purposes when rainfall kinetic energy is derived solely from rainfall intensity data. For longer temporal scales, the relevance of this source of uncertainty remained high if low variability in the types of rain was supposed. Temporal variability of precipitation at wider spatial scales was the main source of uncertainty when rainfall erosivity was calculated on an annual basis, whereas the uncertainty associated with long-term erosivity was rather low and less important than the uncertainty associated with other model factors such as those in the RUSLE, when operationally used for long-term soil erosion modelling.
Highlights
Raindrop impact is the main cause of interrill soil erosion
The results showed that the uncertainty associated with the calculation of rainfall kinetic energy from rainfall intensity at the event and station scales was as high as 30%, because of insufficient information on rainfall drop size distribution
The purpose of this paper is to analyse the diverse sources of uncertainty associated with the calculation of rainfall kinetic energy and erosivity when obtained from precipitation data for a range of temporal and spatial scales, from the event at the station scale to the long-term mesoscale area, for applying a soil erosion model such as the RUSLE (Foster, 2004)
Summary
Raindrop impact is the main cause of interrill soil erosion. Rainfall kinetic energy or some surrogate or derivative is a variable used by most soil erosion models. Wischmeier and Smith (1959), on the basis of rill and interrill erosion measurements in erosion plots, defined rainfall erosivity as a product of event rainfall kinetic energy and depth. Rainfall kinetic energy is obtained from rainfall intensity and raindrop size distribution, normally measured with the flour tray (Laws and Parsons, 1943) or the dyed filter paper (Marshall and Palmer, 1948) methods, on-site continuous electromechanical (Joss and Waldvogel, 1967), optical or microwave disdrometers and remote short radiofrequency wave attenuation methods are increasingly used. Since information on raindrop size distribution is usually not available at the level of weather data, erosion models make use of some procedure to obtain information on rainfall kinetic energy from intensity or depth measurements. At larger and longer-term scales, relationships between (daily, seasonal or annual) precipitation depth and Published by Copernicus Publications on behalf of the European Geosciences Union
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