On the basis of observed river discharge, our studies contribute to a better quantification of the Arctic Ocean Freshwater Budget. Based on 235 gauging stations in the Arctic River Database, 35 rivers have been selected on the basis of representativeness for the calculation of the volume-sum of discharge into the Arctic Ocean. The selected rivers drain an area of 12.9 million km~2 with an annual total discharge of 2603 km~3 into the Arctic Ocean. The gauged area of the selected rivers accounts for 70 % of the Arctic region depicted in Figure 1. The error bandwidth resulting from discharge measurements, the use of different time series and the lack of observations from melting processes and subsurface flows add to the uncertainties associated with the computation of total river discharge into the Arctic Ocean. For the analysis of variability and seasonality as well as for tests on trends and jumps in the time series, four rivers have been selected which account for about 68 % of the volume-sum of river discharge into the Arctic Ocean. Climatic variability markedly influences the timing of the melt period around the month of May, and hence river discharge into the Arctic Ocean. Approximately 79 % of the yearly runoff occurs in the months May -September. The more continental the climate, the more extreme the ratio of minimum to maximum discharge. In monthly series, increases in discharge have occurred from November to April in Siberia and from February to May in North America. A decrease in discharge is only observed in Siberia between July and September, the latter month being common to all rivers. The monthly variability of the volume-sum discharge into the Arctic Ocean cannot be computed with sufficient accuracy due to the inadequate overlap of the time series of the available river records. Only for the Yenisei river significant jumps and trends occur in annual series. The observed jumps and trends in time series need to be further examined for their causality.
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