A SIMPLE-MODEL FOR PREDICTING THE DATE OF SPRING STRATIFICATION IN TEMPERATE AND SUBTROPICAL LAKES

The date of onset of spring stratification in northern hemisphere lakes is predictable from mean annual air temperature. The prediction is further improved by also considering lake surface area (surrogate of wind exposure) and by the ratio (R) of lake surface area to mean depth, with R reflecting aspects of lake morphometry and heat storage capacity. Mean annual air temperature and R together explain 68% of the variance in the date of onset of stratification in a combined 70-lake data set from North America, Europe, and Asia. Nearly identical fractions were explained when the lakes were separated into dimictic and warm monomictic data sets. The remaining unexplained variation is probably largely attributable to interyear variation in weather, but also to unexamined differences in regional wind strength, local protection from winds, lake shape, and lake turbidity, as well as differences in the intervals at which temperature profiles were taken.