Improving Our Understanding of Lake Surface Evaporation

Understanding the Great Lakes system is crucial for the millions of stakeholders that are impacted by the country’s supply of fresh surface water.

But the lakes have been full of surprises lately. Lakes Michigan and Huron rose above their historic average in September 2014, yet the water was at the lowest level ever recorded only two years ago.

CEE researchers are working to improve our understanding of the fluctuating water levels. They suspect the water level drops were primarily caused by evaporation. This is because nearly a third of the Great Lakes basin is lake surface water, and water near the surface heats up and evaporates more easily than water on the land surface.

The researchers involved are Assistant Professor Branko Kerkez and his doctoral student Kevin Fries, CEE Adjunct Professor Andrew Gronewold and LimnoTech Senior Scientist John Lenters. They are developing a better method of measuring lake surface evaporation.

Their project utilizes two separate sensor platforms that can be used together to estimate evaporation:

1) a drifter buoy capable of measuring wind speed, air temperature, surface temperature, and relative humidity
2) a fully equipped, tethered buoy capable of measuring radiation and the temperature at various depths in addition to the other readings.

The fully equipped buoys will remain stationary while the drifter buoys will travel around the lakes with the current. This will enable the team to collect information about correlations between locations, and cover a wider area using fewer sensors. This data will then be transmitted via satellite modem to a cloud-based architecture with open access available to decision makers and researchers.

This means decision makers will know how much water is evaporating within a couple of days and can plan accordingly. For example, water managers can adjust how much water they pump in or out and prevent drastic water level drops or flooding.

This would be a novel improvement over the current system in which evaporation is estimated the season afterwards by calculating it as a residual. 

The project is currently in the prototype deployment phase. They expect to conduct the full-scale deployment between March and November of 2015.

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(Photos from left: One of the prototypes; Kevin Fries and Ho-Zhen Chen on the Third Sister Lake in Ann Arbor, getting ready to deploy a prototype sensor.)

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