Identifying erosive periods with RUSLE factors in Pyrenean fields

Papers published in Hydrology and Earth System Sciences Discussions are under open-access review for the journal Hydrology and Earth System Sciences Abstract The Mediterranean environment is characterized by strong temporal variations in rainfall volume and intensity, soil moisture and vegetation cover along the year. These factors play a key role on soil erosion. The aim of this work is to identify different ero-sive periods in function of the temporal changes in rainfall and runoff characteristics 5 (erosivity, maximum intensity and number of erosive events), soil properties (soil erodi-bility in relation to freeze-thaw processes and soil moisture content) and current tillage practices in a set of agricultural fields in a mountainous area of the Central Pyrenees in NE Spain. To this purpose the rainfall and runoff erosivity (R), the soil erodibility (K) and the cover-management (C) factors of the empirical RUSLE soil loss model 10 were used. The R, K and C factors were calculated at monthly scale. The first ero-sive period extends from July to October and presents the highest values of erosivity (87.8 MJ mm ha −1 h −1), maximum rainfall intensity (22.3 mm h −1) and monthly soil erosion (0.10 Mg ha −1 month −1) with the minimum values of duration of erosive storms, freeze-thaw cycles, soil moisture content and soil erodibility (0.007 Mg h MJ −1 mm −1). 15 This period includes the harvesting and the plowing tillage practices. The second ero-sive period has a duration of two months, from May to June, and presents the lowest total and monthly soil losses (0.04 Mg ha −1 month −1) that correspond to the maximum protection of the soil by the crop-cover (C factor = 0.05) due to the maximum stage of the growing season and intermediate values of rainfall and runoff erosivity, maximum 20 rainfall intensity and soil erodibility. The third erosive period extends from November to April and has the minimum values of rainfall erosivity (17.5 MJ mm ha −1 h −1) and maximum rainfall intensity (6.0 mm h −1) with the highest number of freeze-thaw cycles, soil moisture content and soil erodibility (0.021 Mg h MJ −1 mm −1) that explain the high value of monthly soil loss (0.09 Mg ha −1 month −1). The interactions between the rainfall ero-25 sivity, soil erodibility, and cover-management factors explain the similar predicted soil losses for the first and the third erosive periods in spite of the strong temporal …