Historical runoff variation in the Nordic countries

The regional variability of the runoff in the Nordic countries has been examined by analysing 160 long-term series of daily discharge. The study area was grouped into 13 regions with similar temporal behaviour of the annual runoff. Index series were developed for each region. The series were tested for trend and jumps. An increase has been found in southwest Norway and in Denmark, especially since 1980. Series from southern Sweden show a decrease at the same time. The increase in the maritime exposed areas are most significant in the autumn and early winter. The behaviour of the runoff series has been compared to the behaviour of selected precipitation series. The increase in runoff in southwest Norway is reflected in a similar increase in the precipitation in the same period.