News Feature | January 23, 2015

Scientists Measure Reservoir Evaporation To Gauge Water Scarcity

Sara Jerome

By Sara Jerome,

Scientists are trying out a new approach to drought and water scarcity monitoring: They are measuring how much water evaporates from reservoirs in order to provide a more accurate picture of how much water is available.

The team effort, including the federal government, the California Department of Water Resources, and the Desert Research Institute, is focusing on Folsom Lake, a reservoir near Sacramento. The group is placing a weather station at the lake, according to Capital Public Radio.

"It’s no easy task; the high tech device sits on a buoy that has to be slowly towed out by boat to the deep part of the reservoir," the report said. The buoy is equipped with monitoring equipment.

That includes "temperature sensors, humidity sensors, wind gauges, and net radiometers. But its primary purpose is to measure water evaporation over the reservoir," the report said.

Justin Huntington, a hydrologist with the Desert Research Institute, explained why it is important to understand how much water evaporates.

"Huntington says not knowing...means not knowing how much water could be available for cities and farmland," the report said.

“A ten percent error in evaporation off this reservoir is worth millions and millions of dollars in terms of water to irrigators,” Huntington said, per the report.

This project is different than existing evaporation measurement programs. State regulators already have 145 weather stations in place that monitor evaporation over land. But Huntington said that evaporation over water needs to be studied because it could help determine how much water gets delivered, the report said.

Evaporation is normally measured with a pan placed near water.

“It’s about a four foot wide pan by about a foot deep metal pan usually on a pallet located at the dam and they measure the amount of water loss from that pan every day," Huntington said, per the report. "As you can imagine the evaporation from that pan is probably a lot different than the evaporation occurring over this big body of water.”

California is still in dire straits when it comes to drought, despite rain in recent months.

recent federal analysis "explains that California's drought has receded somewhat, but 98 percent of the state is still in drought — and 32 percent still facing 'exceptional' drought. Worse, it could take near-record amounts of rain this year to pull the state out of its drought," VOX reported.

Agriculture is among the hardest-hit industries.

"After three years of drought, California’s reservoirs are filled with more mud than water. Many farmers can’t irrigate their fields and have no choice but to leave them fallow," Fortune recently reported.

For more on water scarcity, check out Water Online's Water Scarcity Solution Center.