By Gabrielle Rancifer
Medill Reports

“If we didn’t have evaporation, we wouldn’t have water in the atmosphere,” said Thomas Lowell, a geology professor at the University of Cincinnati. 

Researchers closely follow and evaluate both evaporation and precipitation because they are key components of the water cycle. Evaporation delivers water to the atmosphere, and precipitation delivers water to the many systems and bodies that depend on it. The two work to maintain the flows and stands of rivers, lakes and other bodies of water.

Nearly every kid has had a lesson on the water cycle and evaporation in grade school. Although it may seem complex, there are two main portions that make up the water cycle.

“You can summarize what the water cycle does into two things,” said Charles Compton, a biology teacher at Episcopal Collegiate School in Little Rock, Arkansas. “One is evaporation — so we’re getting water from the Earth’s surface into the atmosphere; then second is precipitation — that is water going from the atmosphere back down to Earth.”

“There wouldn’t be any of the water in the atmosphere because that ultimately comes out as rain or snow or ice, and it all has to get there by evaporation,” Lowell said. “There’s no magic bucket of water in the atmosphere; it’s a balance between what goes up and what comes down.” 

Lowell shared his research on evaporation in a presentation titled “Toward Paleo P/E” this fall at the Comer Climate Conference, an annual gathering of global climate scientists held virtually for the third year due to COVID-19. During the presentation, Lowell emphasized the importance of regional hydrology and evaporation.

The water cycle is “the path that all water follows as it moves around Earth in different states. Liquid water is found in oceans, rivers, lakes — and even underground,” according to NASA.

All bodies of water — lakes, rivers, creeks, bayous, seas, oceans — depend on the water cycle. The movement of water and the maintenance of water systems depend upon evaporation. Climate scientists, such as Lowell, look at how climate change impacts the water cycle and evaporation. 

The atmosphere can hold only so much water until it returns to the Earth as rain or snow. However, as the average global warming temperature increases, the atmosphere’s ability to hold water does the same; thus, the amount of water that falls from the clouds inherently increases, Lowell pointed out. Given that water can evaporate from various water bodies, they could lose volume — sometimes even permanently. 

Paleolakes — lakes that existed in the past but have since dried up or are drying up — reveal climate conditions correlated to climate processes. These processes often reflect the balance of evaporation and rainfall. Scientists study what happened in the past better to understand threats to current lakes and other water sources. 

At the University of California, Berkeley’s Geochronology Center, Guleed Ali, a postdoctoral researcher, studies Mono Lake, a paleolake on the eastern edge of California’s Sierra Nevada. Ali finds imbalanced evaporation to be a threat — especially in the West. 

“It (evaporation) is probably one of the components that is a major driving force for concern,” Ali said. “With warming, owing to anthropogenic greenhouse gas emissions, there can be more evaporation of water across the landscape — so lower soil moisture. It can also lead to more evaporation from lake surfaces, and the whole area could get much dryer than it was before.” 

Those anthropogenic emissions are largely carbon dioxide produced from human reliance on petroleum-based fuels. Ali is studying the tufa formations of calcium carbonate to date changes in climate and lake levels. The tufa bands show previous high lake levels, but they never were replenished back to previous high stand levels, he said. 

Granted, this paleo lake took thousands of years to reach its current level. So, while the volume of our water systems will not lose hundreds of thousands of gallons in the next week, Mono Lake embodies what could happen if humans do not find a way to decrease their carbon impact and slow climate change, as Ali’s research shows. The atmosphere and Earth need to cool to lessen the threat of evaporation becoming more of a negative than a positive in the water cycle. 

At the end of the day, yes, evaporation undoubtedly impacts water systems, and when imbalanced, it could jeopardize the amount made available to humans via precipitation. For evaporation to remain a positive and replenishing contributor to the water cycle, climate change must slow or, better yet, halt. 

Gabrielle Rancifer is a Health, Environment & Science graduate student at Medill. You can follow her on Twitter at @GabiRancifer and https://grancifer.medium.com/