Variability of Air Temperature, Precipitation and Outflows in the Vistula Basin (Poland)

This study examines trends in temperature, precipitation and discharge rates over a 65-year observation period (1951-2015) and compares the two sub-periods 1951-1980 and 1981-2015. The research was carried out on annual and monthly values. The research area is the basin of the Vistula, the largest river in Poland. The main aim of the study was to assess how changes in air temperature and precipitation in the Vistula basin have translated into river hydrology. In the 65-year study period, a lack of statistically significant trends in outflow prevailed. Compared to the full period 1951-2015, the sub-period 1951-1980 stood out for its statistically significant increase in annual average outflows. In the years 1981-2015 a slight falling trend in outflow of the Vistula was noted, though the values were not statistically significant. This was caused by significant warming during this period (an increase in air temperature of between 0.27 and 0.45 degrees C per decade, depending on location) and a slight increase in precipitation. Seasonal changes in outflows were more volatile. The results indicate that the Vistula's water resources have fallen slightly as a result of changes in air temperature and precipitation and due to the river's significant hydrological inertia, which in turn results from the catchment being very large and physiographically diverse.