Hydrological variability of Finnish free-flowing rivers

River discharges and ice cover strongly impact biotic and abiotic processes in fluvial environments. Hydrometeorological circumstances affect discharges and under climate change, they are changing in high-latitude areas of the globe. During the past decades, spring snowmelt has started earlier in Northern Europe, leading to a shift in the timing of floods and discharge peaks. Also, higher wintertime discharges have been measured. However, little is known about how these changes in the variability and trends have occurred during the past decades (up to 100 y.) and how they will evolve in the future.

The goal of this paper is to understand how the hydrological variability of free-flowing rivers has changed from the past to the present in Finland. To achieve the goal, long-term data on flood magnitude, frequency, and timing are statistically analyzed to identify the hydrological variability of Finnish free-flowing rivers. Previous works showed that discharge parameters work as reliable indicators for assessing long-term changes caused by climate change when combined with weather parameters, teleconnection patterns, and river ice data. Open-access data from 45 gauging stations in 25 different watershed areas were used. The timespan of datasets varies between 40 and 100 years. The results of this paper can be applied when future changes and adaptation methods related to river discharges are considered in the boreal-subarctic climate region.