Long-term variation of rainfall erosivity in Calabria (Southern Italy)

The changes in rainfall erosivity have been investigated using the rainfall erosivity factor (R) proposed for USLE byWischmeier and Smith (RW-S) and some simplified indexes (the Fournier index modified by Arnoldus, F, a regional index spatial independent, RFr, and a regional index spatial dependent, RFs) estimated by indirect approaches. The analysis has been carried out over 48 rainfall stations located in Calabria (Southern Italy) using data collected in the period 1936–2012 and divided in three sub-periods. The series of the erosivity indexes and of some precipitation variables have been analyzed for evidence of trends using standard methods. The simplified indexes suggested a general underestimation of the rainfall erosivity with respect to RW-S. The mean underestimation ranged between 23 and 54 % for RFr and from 10 to 15 % for RFs. Both the sign and the magnitude of the trends were different for the different stations depending on the variable and sub-period considered. In general, the erosivity increased during the period 1936–1955 (1st sub-period) and during the more recent sub-period (1992–2012, 3rd sub-period), whereas it decreased during 1958–1977 (2nd sub-period). The evidence of trends was generally higher for RW-S than for RFr and RFs. Focusing on the most recent sub-period (3rd subperiod), all the variables analyzed showed mainly increasing trends but with different magnitude. More particularly, RW-S showed a mean increment of 29 %; F, RFr and RFs increased by 11, 15 and 18 %, respectively; the maximum intensity of 0.5-h precipitation increased by 5 %; and the annual precipitation increased by 22 %. Consequently, it remains difficult to define which precipitation variable plays the dominant role in the temporal variation of rainfall erosivity in the region. However, the overall results suggest that the indexes estimated by indirect procedures (F, RFr, and RFs) should be used with caution for climate change analysis, despite they are used for practical purposes considering they are based on easily available information.