## 3 Results and Discussion
### Comparison of National vs. European Soil Erosion Map  
This dilemma of missing standardization and harmonization calls for a larger scale model application. Such a challenging approach was published by [PERSON] et al. [19] using an adapted version of the RUSLE and providing publicly available soil erosion information for the entire EU in a 100 m \(\times\) 100 m grid ([[https://esdac.jrc.ec.europa.eu/content/soil-erosion-water-rusle2015](https://esdac.jrc.ec.europa.eu/content/soil-erosion-water-rusle2015)]([https://esdac.jrc.ec.europa.eu/content/soil-erosion-water-rusle2015](https://esdac.jrc.ec.europa.eu/content/soil-erosion-water-rusle2015))). In general, the model results of this study showed higher mean erosion for all sites and applied model approaches. The differences were most pronounced between the European map and the AT and CZ approach (Figure 3; column on the right). A field-by-field comparison (Figure 4D,H,L) gives more insights into why the national/regional approaches differ substantially from the European map. At the site in Bavaria and Austria, which both are dominated by small fields (mean size: 3.1 ha and 2.2 ha, respectively), the European map overestimates the erosion on fields with little erosion while it underestimates the erosion on fields with substantial erosion (Figure 4D,H,L). Differences in erosion of individual fields results to a large extend from differences in \(LS\) factor. A raster cell size of 25 m \(\times\) 25 m used to calculate the \(LS\) factor which is then aggregated into the 100 m \(\times\) 100 m European map substantially smoothens the slope variability and hence must lead to an underestimation of steep and overestimation of flat slopes. This relation was shown in several earlier studies [56; 57]. The effect is much smaller in the CZ test catchment as the mean field size of 11.6 ha is much larger and hence aggregating erosion to field means already results in an averaging of steep and flat areas within these fields. In consequence, the correlation between the CZ site modelled with the CZ method and the European map is much stronger (R\({}^{2}\) = 0.30; \(p\) < 0.001) than at the BY and AT sites using the respective regional methods (R\({}^{2}\) = 0.12 and 0.15; \(p\)< 0.001). The available input data for the European map is highly fragmented due to major rational differences in data sources and data accuracies. For a homogenized pan-European soil erosion map, assumptions are required that include high uncertainties (e.g., [58]). Moreover, region-specific adaptations and optimizations of the USLE (see examples in methods) cannot be considered in a harmonized procedure for the entire EU.  
However, apart from the scale issue, the European map shows generally much smaller erosion means as compared to the national/regional approaches (Figure 4D,H,L). For the Bavarian and the Czech site, the [PERSON] et al.'s [19] map shows a mean erosion of 5.64 and 4.17 ha\({}^{-1}\) a\({}^{-1}\), which is about 30% and 70% less erosion compared to the site-specific modelling. This would of course lead to much softer requirements to farmers to apply soil conservation techniques and measures in these catchments. Hence, there seems to be still a strong need for more cooperation and homogenization of data and methods to bridge the gap between national and EU-wide input data and methodologies.