Review of methods of spatio-temporal evaluation of rainfall erosivity and their correct application

Rainfall erosivity factor (R) is the key part of both the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE). Its accuracy is related to the rainfall kinetic energy equation, the number of rain gauge stations, spatial distribution of rain gauge stations network, type of rain gauges, recording temporal resolution, the time step of rainfall intensity used, used time period, type of interpolation method, used covariates for determination of R values at unmeasured places, and way of regionalisation of R values or its determination for a given locality. These aspects are described, compared and discussed, including several common discrepancies and distortions. All approaches to R factor computation and estimation are presented with a focus on central Europe. The approaches were divided into two groups: the first low temporal resolution approach (yearly daily rainfall totals), and the second high temporal resolution approach (1-60 min rainfall totals). The relationship between the spatio-temporal distribution of R-and cover-management factor (C) values is described, including other methods of C-factor estimation. Several methods of R-and C-factor estimation and calculation were developed due to the lack of optimal data required by the original methodology or due to incorrect interpretation of given parameters or criteria. Also, inappropriate integration with the geographical information system (GIS) tools and Remote Sensing (RS) data may cause many simplifications and distortions of the original principles of the USLE/RUSLE. This review should help to choose the appropriate methodology of R-and C factor calculation in the field of water erosion risk assessment and help to reach a more appropriate allocation of financial expenses of erosion control measures.