Rainfall erosivity in Madeira Island. Analysis of the 20 February 2010 catastrophe

Abstract

To assess local or regional potential erosion, an adequate indicator is the rainfall erosivity parameter (R) of RUSLE. The Madeiras island catastrophe of 20 February 2010, with intense debris flows was responsible for devastation and losses of lives; efforts have been made to analyze the event and to evaluate the distributed erosion. The RUSLE methodology was adopted, however the key issue was obtaining the distributed values of R, both for the event and on a yearly basis. Funchal-Observatório is the only meteorological station available with long records and precipitation data with 10 minute discrimination (last 10 years), to enable the calculation of the erosivity, by event and on daily and monthly basis. This station has also hourly records for more than 20 years and daily records exist since the middle 1930s.. Due to the scarcity of data, correlations were established to estimate erosivity for larger periods and assess erosivity in other locations. The established methodology allowed calculation of RUSLE erosivity parameter on yearly and event basis, in Madeira. Comparisons were made with previously estimations obtained for Portugal. The procedure showed good robustness and a proposal to deal with cases of data scarcity is presented.