Winter atmospheric circulation and river discharge in northwest Europe

More frequent western atmospheric circulation over Europe results in increased precipitation in winter, and could result in increasing river discharges. We made a quantitative assessment of the impact of variation in atmospheric circulation, defined by the frequency of western circulation in the Gro ss wetterlagen classification system and the North Atlantic Oscillation (NAO) index, on variation in basin-average precipitation and winter discharges (December-February) of eleven large river basins that drain northwest Europe. Annual winter discharges amounts are highly correlated among these rivers (up to r(2) = 0.82, decreasing with increasing inter-basin distance), which may point to a common atmospheric forcing. The number of days of western atmospheric circulation in winter as indicated by the Gro ss wetterlagen classification system is more closely related (r(2) = 0.06 to r(2) = 0.28, p < 0.05 or better) to winter river discharges than the NAO index. We therefore conclude that the frequency of western atmospheric circulation over Europe is a better indicator of climate variability and climate change impacts on river discharges in northwest Europe.