Recent lake ice-out phenology within and among lake districts of Alaska, U.S.A.

The timing of ice-out in high latitudes is a fundamental threshold for lake ecosystems and an indicator ofclimate change. In lake-rich regions, the loss of ice cover also plays a key role in landscape and climatic processes.Thus, there is a need to understand lake ice phenology at multiple scales. In this study, we observed ice-out timingon 55 large lakes in 11 lake districts across Alaska from 2007 to 2012 using satellite imagery. Sensor networks intwo lake districts validated satellite observations and provided comparison with smaller lakes. Over this 6 yrperiod, the mean lake ice-out for all lakes was 27 May and ranged from 07 May in Kenai to 06 July in ArcticCoastal Plain lake districts with relatively low inter-annual variability. Approximately 80% of the variation in iceouttiming was explained by the date of 0uC air temperature isotherm and lake area. Shoreline irregularity,watershed area, and river connectivity explained additional variation in some districts. Coherence in ice-outtiming within the lakes of each district was consistently strong over this 6 yr period, ranging from r-values of 0.5to 0.9. Inter-district analysis of coherence also showed synchronous ice-out patterns with the exception of the twoarctic coastal districts where ice-out occurs later (June–July) and climatology is sea-ice influenced. These patternsof lake ice phenology provide a spatially extensive baseline describing short-term temporal variability, which willhelp decipher longer term trends in ice phenology and aid in representing the role of lake ice in land and climatemodels in northern landscapes.