Changes in water temperature and ice phenomena in the Ner river (central Poland) in the years 1965-2014

Abstract

The paper presents long-term changes in water temperature and ice conditions in the Ner River located in Central Poland. A considerable increase in water temperature has been determined over the last fifty years, amounting to 0.24 °C dek-1. The increase was statistically significant at a level of p=0.05. In the monthly scale, the highest increase in temperature was recorded in July (0.37 °C dek-1), April (0.35 °C dek-1), and December and January (0.34 °C dek-1). In two cases (September and October), a slight negative tendency was recorded, although it was not statistically significant. In reference to the terms of appearance of ice phenomena, a delay by 1.9 day・dek-1 was determined in the analysed period. The cessation of ice phenomena showed a negative tendency – they ceased earlier by 2.5 day・dek-1. Due to this, the persistence of ice phenomena was reduced. The recorded changes are a result of an increase in air temperature and anthropopressure.