Trends and variability in unregulated streamflow in Finland
// 16th international symposium and workshop "Northern research Basins". Petrozavodsk: KarRC RAS, 2007. Pp. 66-73
Keywords: Discharge, trends, variability, Finland, rivers, lake outlets
This paper presents long-term discharge trends and variability for thirteen time series including both rivers and lake outlets in Finland. These unregulated discharge time series were studied for the longest available period until year 2004 and for the period 1961-2004. The longest discharge time series date back to the mid-1800s. The aim of this study was to examine observed changes and variability in the Finnish discharge regime until so far. The discharge peak flow usually occur in the south in April and in the north in June. In northern Finland the maximum flow of the year is always due to snow melt, but in the southern Finland summer, autumn and winter high flows are also possible. The Mann-Kendall trend test was applied to study changes in annual, monthly and seasonal mean discharges, maximum and minimum flows and in addition the date of peak flow. The trend analysis showed no changes in mean annual flow in general, but the seasonal distribution of streamflow have been shifted. Winter, spring and minimum discharges have increased at least half of the observation sites. The magnitude of increase in winter and spring discharges was 2…10 % per decade. The spring peak has moved earlier for the third of the studied sites with magnitude of 1…3 days per decade.