A FILA column reader recently posed a question that is the subject of this week’s column. The person wanted to know if evaporation occurs in the lake during winter.
The obvious answer is that in no way can water evaporate. A thick cover of ice usually covers the water from shore to shore. In doing some research it seems that answer is not at all definitive.
It turns out that there have actually been studies done to determine what happens with evaporation during the winter months. First, it is important to understand the importance of evaporation. The following is from the USGS -Science for a Changing World website. “For the water cycle to work, water has to get from the Earth’s surface back up into the skies so it can rain.” Studies have shown that the oceans, seas, lakes and rivers provide nearly 90% of the moisture in the atmosphere via evaporation.
“Many people assume that the Great Lakes’ highest rate of evaporation are in the heat of summer since high temperatures are often equated with high rates of evaporation. It turns out, that this is simply not the case. The highest evaporation rates on the Great Lakes occur in late fall and early winter. This is because evaporation is not directly driven by warm temperatures, but instead by warm water temperatures.
Evaporation requires three factors: 1) a large temperature difference between water and air, 2) low relative humidity, and 3) high wind speeds. If all three ingredients are present, as often occurs in the fall and early winter, (before ice forms) evaporation occurs.
There is a complex interaction among evaporation, ice cover and water temperatures which demonstrates that ice cover does not simply act as a cap on evaporation, as has been assumed. Rather, the cooling effects of evaporation exert important feedbacks on lake temperatures and ice cover that can actually result in above-normal evaporation rates immediately prior to winters with high ice cover. Conversely, winters with low ice cover are typically followed by warm summer water temperatures and an early start to the evaporation season.”
(Information from “Assessing the Impacts of Climate Variability and Change on Great Lakes Evaporation” – a study by Great Lakes Evaporation: Implications for Water Levels.” )
As local anglers, snowmobilers, cross-country skiers and other winter enthusiasts wait for Five Island Lake to freeze, it is apparent that this late fall has indeed had the ingredients for lake evaporation.
Previous question’s answer: Actually, there were two elected officials that were instrumental in helping to complete the dredging in the north part of the lake. These individuals were Iowa State Senator Jack Kibbie and State Representative Marci Frevert.
Question: What soil type was a result of the silt dredged from the north portion of Five Island Lake?
Written by Diane Weiland
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