Changes in ice phenology characteristics of two Central European steppe lakes from 1926 to 2012-influences of local weather and large scale oscillation patterns

Ice cover of the two Central European steppe lakes, Lake Balaton (Hungary) and Lake Neusiedl (Austria/Hungary), is characterized by high interannual variability (mean ice duration +/- s.d.: 44 +/- 26 days and 73 +/- 28 days, respectively). For both lakes, a trend towards shorter ice duration and earlier ice-off can be observed in the 86 and 81 year data records, respectively. For Lake Neusiedl, significant trends for ice-on (+2.3 days decade (-1)), ice-off ( -1.8 days decade (-1)) and ice duration (-3.1 day decade (-1)) are detected. At Lake Balaton, however, trends for ice-on (0 day decade (-1)), ice-off (-0.7 days decade (-1)) and ice duration ( -1.2 days decade (-1)) are not significant. The temporal trends have accelerated for Lake Neusiedl in the past 60 years (ice duration -5.6 days decade (-1)). The variability of the ice parameters has increased during the 80 year observation period for Lake Neusiedl, but not for Lake Balaton. The number of melt-refreeze cycles at Lake Balaton increased at first, but then decreased during the last 20 years at both lakes. Warming trends in mean surface water temperatures for all seasons are more distinct than temporal trends of mean air temperatures. Increases of winter air temperature by 1 degrees C are related to an ice-on delay, a decrease in ice duration (Lake Balaton: -12 days degrees C (-1), R-2=0.72; Lake Neusiedl: -11 day degrees C (-1), R-2=0.54) and an earlier ice-off. Snow cover, wind speed, and solar radiation are also related to ice dates.