Trends of ice breakup date in south-central Ontario

Large-scale ice phenology studies have revealed overall patterns of later freeze, earlier breakup,and shorter duration of ice in the Northern Hemisphere. However, there have been few studies regardingthe trends, including their spatial patterns, in ice phenology for individual waterbodies on a local or smallregional scale, although the coherence of ice phenology has been shown to decline rapidly in the firstfew hundred kilometers. In this study, we extracted trends, analyzed affecting factors, and investigatedrelevant spatial patterns for ice breakup date time series at 10 locations with record length ≥90 years insouth-central Ontario, Canada. Wavelet methods, including the multiresolution analysis (MRA) method fornonlinear trend extraction and the wavelet coherence (WTC) method for identifying the teleconnectionsbetween large-scale climate modes and ice breakup date, are proved to be effective in ice phenologyanalysis. Using MRA method, the overall trend of ice breakup date time series (1905–1991) varied from earlierice breakup to later ice breakup, then to earlier breakup again from south to north in south-central Ontario.Ice breakup date is closely correlated with air temperature during certain winter/spring months, as well asthe last day with snow on the ground and number of snow-on-ground days. The influences of solar activityand Pacific North American on ice breakup were comparatively uniform across south-central Ontario, whilethose of El Niño–Southern Oscillation, North Atlantic Oscillation, and Arctic Oscillation on ice phenologychanged with distance of 50–100 km in the north-south direction.