Monthly R-factor and Conversion factors for different time resolutions

As a follow up and an advancement of the recently published Rainfall Erosivity Database at European Scale (REDES) and the respective mean annual R-factor map, the monthly aspect of rainfall erosivity has been added to REDES. Rainfall erosivity is crucial to be considered at a monthly resolution, for the optimization of land management (seasonal variation of vegetation cover and agricultural support practices) as well as natural hazard protection (landslides and flood prediction). We expanded REDES by 140 rainfall stations, thus covering areas where monthly R-factor values were missing (Slovakia, Poland) or former data density was not satisfactory (Austria, France, and Spain).REDES includes 1675 stations with R-factor values in European Union & Switzerland. The different time resolutions (from 5 to 60 min) of high temporal data require a conversion of monthly R-factor based on a pool of stations with available data at all time resolutions.The coefficients of different resolutions for monthly rainfall erosivity allow normalizing the monthly R-factor values to a common 30-min resolution for all the REDES stations.

Calibration factors for different temporal resolutions (Annual basis)

The term ‘calibration factor’ is used below to represent this conversion between the R-factor at different resolutions and the R-factor at 30-min.The different time resolutions (from 5 to 60 min) of high temporal data require a conversion of monthly R-factor based on a pool of stations with available data at all time resolutions.

Resolutin of source data Target resolution Conversion factor
1-min 30-min 0.7496
5-min 30-min 0.7984
10-min 30-min 0.8205
15-min 30-min 0.8716
60-min 30-min 1.5597

 

Monthly calibration factors for different temporal resolutions

The 'calibration factor' on monthly basis shows high variability. For example this factor using the 60-min data ranges from 1.2974 (January) to 1.6995 (August). For the 10-min data, the calibration factor ranges between from 0.7986 (July) to 0.8951 (January). (August). The smallest calibration factors are estimated in winter, while the largest ones are found. Compared with using one single calibration factor for the whole year, the option to apply monthly calibration factors is recommended, as there is 25% variability in the monthly conversion factors.

Calibration factors

 

Seasonal Rainfall Erosivity

Within Europe, geographic differences exist in the seasonal patterns of rainfall erosivity. The stations with the absolute largest R-factor value in a single month (for instance July, August, September or October) are located mostly in Italy and Slovenia. For each REDES station, the season (spring, summer, autumn, winter) with the largest R-factor has been selected (Figure below). For 94% of the REDES stations, the most erosive period is either summer (68%) or autumn (26%). For only 22 REDES stations, mainly located in South Spain and France, the most erosive period is spring.

R-factor regional patterns

The June to September period contributes to 53% of the annual rainfall erosivity in Europe, with different spatial and temporal patterns depending on the region. The R-factor shows the largest monthly values in autumn across most of the Mediterranean region, where the precipitation amount is generally larger in October–November and summers are frequently hot and dry. The R-factor is largest in summer in Central Europe, Northern Europe, Eastern Europe and the Alps. This pattern might have different explanations, as Central Europe is generally affected by large-scale  extreme precipitation events in summer, while the Alps are usually affected by local summer thunderstorms and rain showers, due to the remarkable temperature gradients between hot and moist lowlands and cool and windy mountains. Similar patterns can be found in the Carpathians and Eastern Europe. The Atlantic regions do not show distinctive patterns, probably because the monthly precipitation variability is smaller than in the continental regions, especially in the British Islands.  candinavia shows higher variability in summer, but one should not forget that in winter, the precipitation events at high-latitudes are often in the form of snowfall and so we expect much fewer erosive events in winter compared to summer.

Monthly maps of rainfall erosivity in European Union & Switzerland have been developed and will be available soon.

Detailed inormation and regional patterns of monthly rainfall erosivity can be found in:

Panagos, P., Borrelli, P., Spinoni, J., Ballabio, C., Meusburger, K., Beguería, S., Klik, A., Michaelides, S., Petan, S., Hrabalíková, M., Olsen, P., Aalto, J., Lakatos, M., Rymszewicz, A., Dumitrescu, A., Tadic, M.P.,  Diodato, N., Kostalova, J., Rousseva, S., Banasik, K. Alewell, C.  2016. Monthly rainfall erosivity: conversion factors for different time resolutions and regional assessments. Water, 8(4), No 119.