River Discharge into the Mediterranean Sea: Climatology and Aspects of the Observed Variability

Abstract

River discharge across the Mediterranean catchment basin is investigated by means of an extensive dataset of historical monthly time series to represent at-best discharge into the sea. Results give an annual mean river discharge into the Mediterranean of 8.1 ? 103 m3 s?1, or at most a value that should not exceed 10.4 ? 103 m3 s?1. The seasonal cycle has an amplitude of 5 ? 103 m3 s?1, with a dry season in midsummer and a peak flow in early spring. Dominant contributions are from Europe with a climatological annual mean of 5.7 ? 103 m3 s?1. Discharge in the Adriatic Sea, the Gulf of Lion, and the Aegean Sea together account for 62% of Mediterranean discharge, which mostly occurs in the Adriatic (2.7 ? 103 m3 s?1). The North Atlantic Oscillation (NAO) impacts Mediterranean discharge primarily in winter, with most river discharges across the Mediterranean catchment being anticorrelated with the NAO. Related winter anomalies are about 10%?20% of the winter means. During the period 1960?90, Mediterranean winter discharge as a whole may have undergone year-to-year NAO-related variations of up to 26% of the seasonal mean, while about 17% on decadal time scales. These variations are expected to have occurred mostly in the Gulf of Lion and the Adriatic Sea, together with the Balearic Sea, where the impact of the NAO is greatest.