Monthly erosivity

Rainfall erosivity as a dynamic factor of soil loss by water erosion is modelled intra-annually for the first time at European scale. The development of Rainfall Erosivity Database at European Scale (REDES) and its 2015 update with the extension to monthly component allowed to develop monthly and seasonal R-factor maps and assess rainfall erosivity both spatially and temporally. During winter months, significant rainfall erosivity is present only in part of the Mediterranean countries. A sudden increase of erosivity occurs in major part of European Union (except Mediterranean basin, western part of Britain and Ireland) in May and the highest values are registered during summer months. Starting from September, R-factor has a decreasing trend. The mean rainfall erosivity in summer is almost 4 times higher (315 MJ mm ha−1 h−1) compared to winter (87 MJ mm ha−1 h−1).

The Cubist model has been selected among various statistical models to perform the spatial interpolation due to its excellent performance, ability to model non-linearity and interpretability. The monthly prediction is an order more difficult than the annual one as it is limited by the number of covariates and, for consistency, the sum of all months has to be close to annual erosivity. The performance of the Cubist models proved to be generally high, resulting in R2 values between 0.40 and 0.64 in cross-validation. The obtained months show an increasing trend of erosivity occurring from winter to summer starting from western to Eastern Europe. The maps also show a clear delineation of areas with different erosivity seasonal patterns, whose spatial outline was evidenced by cluster analysis. The monthly erosivity maps can be used to develop composite indicators that map both intra-annual variability and concentration of erosive events. Consequently, spatio-temporal mapping of rainfall erosivity permits to identify the months and the areas with highest risk of soil loss where conservation measures should be applied in different seasons of the year.

Rainfall erosivity is mapped intra-annually for the first time at European scale. The monthly erosivity maps  depict a quite large difference in erosivity. Across Europe, a comparable difference is present in the temporal dimension where the same area can have values of R orders of magnitude dissimilar in different times of the year.

With the exception of the Mediterranean basin, the general spatial patterns of rainfall erosivity both in seasonal maps and monthly maps  exhibit a smooth increase of R-factor from winter to spring, followed by a sharp intensification in summer and then a smooth decrease in autumn. The highest divergence is noticed in autumn (followed by winter) with low mean values in Central and Northern Europe and very high values in the southern part. The objective of the seasonal R-factor maps is to show the seasonal patterns in European Union.

 

Monthly erosivity and composite indicators

The monthly erosivity maps allowed the development of indicators for studying the intra-annual variability of erosivity and the concentration of erosive events. Those composite indicators are the  
a) Seasonal erosivity by Köppen-Geiger climate classification and cluster analysis b) Ratio between lowest and the highest erosivity c) Weighted erosivity density and Coefficient of Variation (CV) of monthly erosivity density d)  Months with highest and lowest erosivity

Seasonal erosivity by Köppen-Geiger climate classification and cluster analysis: A different approach is to use the R-factor values itself to identify relatively homogeneous areas in terms of rainfall erosivity seasonal patterns by cluster analysis. Clusters capture most of the variability of the R-factor in Europe. The fact that different clusters represent quite different precipitation regimes can be evidenced by plotting values of R-factor densities by month and cluster.

Ratio between lowest and the highest erosivity: While the monthly erosivity maps give a general idea about the areas with the highest variability in rainfall erosivity across the year, a better understanding can be obtained by creating amap of the ratio between the lowest and the highest erosivity values.

Weighted erosivity density: An assessment of the distribution of erosivity over the year is critical for management and mitigation procedures, so the development of composite indicators expressing not only the yearly estimate, but also the relative impact of extreme events is critical for soil conservation. In this study, we attempted to develop a composite indicator summarizing the intra-annual variability as well as its dependence by extreme events. This indicator is expressed as the ratio between annual erosivity density and the Coefficient of Variation (CV) of monthly erosivity density.

Months with highest and lowest erosivity:  Another essential information about rainfall erosivity is the time of the year when erosivity is at its maximum as well as when it is at its minimum.
 

References

Ballabio, C., Borrelli, P. ,  Spinoni, J.,  Meusburger, K., Michaelides, S.,  Beguería, S., Klik, A., Petan, S., Janecek, M., Olsen, P., Aalto, J.,  Lakatos, M., Rymszewicz, A., Dumitrescu, A.,  Tadić, M.P., Nazzareno, D.,  Kostalova, J., Rousseva, S., Banasik, K., L., Alewell, C. , Panagos, P. 2017. Mapping monthly rainfall erosivity in EuropeSci Total Environ. 579: 1298-1315.

Data

Download the Monthly, seasonal erosivity datasets and the composite indicators described above from: http://esdac.jrc.ec.europa.eu/content/rainfall-erosivity-european-union-and-switzerland

Download the presentation of "Seasonal variation and climate change impact in Rainfall Erosivity across Europe"

 

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