Association between anomalies of moisture flux and extreme runoff events in the south-eastern Alps

The aims of the paper are (i) to describe the annual distribution of extreme runoff events on the Mura, Drava and Sava Rivers, (ii) to demonstrate their association with moisture fluxes, and (iii) to explain their annual distribution by moisture flux climatology. Extreme runoff events were defined as rapid increases in daily mean discharge. Moisture flux anomalies were studied within six pixels of the ERA-40 database around the studied region. In general, extreme runoff events were concentrated in the summer and autumn and were usually associated with anomalies in moisture flux, mainly from the south. Nevertheless, while southern and western moisture fluxes were typical of Sava River events that occurred mainly in autumn, summer events prevailed on the Mura River and were frequently associated with moisture fluxes from the east or the north. It is remarkable that moisture fluxes from the west and south have their maxima in the autumn, whereas those from the east and north have their maxima in the summer. Therefore, the climatology of moisture flux seems to be one of the major reasons for the annual distribution of extreme runoff events in the study region. This result should be confirmed in other regions in the future.