Determinants of temporal coherence in the satellite-derived 1987-1994 ice breakup dates of lakes on the Laurentian Shield
Remotely sensed ice breakup dates for 62 lakes on the Laurentian Shield were analyzed to preliminarily assess determinants of the mean breakup date and to identify determinants of temporal coherence of lake- ice breakup. Correlations between mean breakup date and the explanatory variables (surface area, maximum depth, surface area : maximum depth ratio, latitude, longitude, and elevation) revealed that only latitude (r = 0.96) and surface area (r = 0.45) were significant at P I 0.05. Latitude and surface area were significantly correlated (r = 0.42). The temporal coherence of breakup dates between each pair of lakes was calculated by taking the product- moment correlation between their 8-yr time series (1987-1994) of breakup dates. There is a general lack of strong temporal coherence between lakes, implying that no lake in this study area is representative of the entire region. The significant (P I 0.05) correlates of the temporal coherence of breakup dates were difference in mean breakup date (-0.49) and difference in latitude (r = -0.5 l), themselves significantly correlated (Y = 0.89). The differences in surface area, maximum depth, surface area : maximum depth ratio, longitude, and elevation were not significant. The general lack of strong temporal coherence between lakes and the significant correlation between coherence and mean breakup date are further confirmation that breakup dates for different lakes may be reflections of (and indicators for) different periods of meteorological forcing.