Ice regime dynamics in the Nemunas River, Lithuania

Ice cover persistence in the lower reaches of the Nemunas River has decreased during the last 150 yr. The variation in the river freeze- and break-up dates is related to climatic variables. The significance of the negative break-up trend exceeds that of the positive freeze-up trend. Low-frequency large-scale atmospheric circulation patterns such as the North Atlantic Oscillation and Arctic Oscillation (NAO/AO) appear to have more influence on the break-up date than on the freeze-up date. Different classification methods applied to the atmospheric patterns prevailing in the early freeze-up events reveal similar results; however, differences arising between classifications are attributable to non-persistent and high frequency patterns.