Water is essential for life as we know it. But freshwater, the stuff we drink and use to grow crops, makes up just 2.5 percent of the Earth’s water, according to the US Geological Survey.
Is that enough? How are humans manipulating this vital natural resource? And just how much are we using?
Scientists set out to figure just how big the global freshwater footprint really is. That footprint could be more significant than previously thought, and it might just be because we’re trying to control it.
According to data gathered from water basins across the globe, human attempts to control freshwater by damming waterways and irrigating crops could actually increase water consumption.
The scientists specifically looked at how much water is released back into the atmosphere through evapotranspiration, the process through which liquid water on Earth is released as vapor into the atmosphere, in and around human created reservoirs and irrigation systems, categorizing this as human consumption of water.
The liquid water lost to the atmosphere as water vapor from these dammed waterways and irrigated fields raises the global human freshwater footprint by about 18 percent, according to a paper published Thursday in the journal Science.
“As you have a lot of consumption, and you’re sending this water back to the atmosphere, it’s less water that’s available on the rivers, in the streams, so it’s actually well linked to water availability on Earth,” study author Fernando Jaramillo tells The Christian Science Monitor in an interview. “We are doing something big to the water cycle.”
How does it all work?
Think back to elementary school science. You likely learned about the water cycle, a process in which water changes states.
In the water cycle, water changes from liquid to vapor via evaporation or transpiration, the process by which plants turn liquid water into vapor, moving the water from the surface of Earth to the atmosphere. Then, that water vapor condenses into liquid drops or freezes into snowflakes, precipitation, and falls back down to Earth.
But here’s the catch, that water could fall anywhere on the planet. It could top high mountains in the form of snowcaps, it could fill lakes and spill into rivers, or it could land in the salty ocean, where it stops being freshwater.
So, especially in regions where people are already struggling to find access to freshwater, this big footprint could be bad news.
Over the period of 1955 to 2008, freshwater was consumed by humans at an average rate of about 4,370 cubic kilometers each year, or 1048 cubic miles each year, the scientists report. That’s up 3,563 cubic kilometers per year from 1901 to 1954.
Planetary boundaries have been proposed by researchers as limits to which humans can sustainably use resources. By Dr. Jaramillo and colleague Georgia Destouni’s estimates, that proposed boundary is 4000 cubic kilometers per year, which we've already passed.
But, says Jaramillo, “There’s still a lot of things to study. We have only studied two types of land use and water use developments.”
He hopes to see more research on water use in the future. “This is a large scientific field that’s just starting to grow,” Jaramillo says. “It’s incredible that water is so important to us and we still don’t know how much water we are consuming. That’s ridiculous.”
“Humans need water for living. We are made out of water,” Jaramillo says. “We need water for drinking, we need water for food production, and we also need water to feed the crops that feed us.” We even use water to make electricity, he adds.
“That’s not taking into account the water that terrestrial ecosystems needs,” Jaramillo says. “All vegetation needs water.”
“We’re taking water away from the natural system for our purposes, without thinking what’s happening with all these other organisms and living things that are based on those water,” he says.
Further research about humanity’s freshwater footprint could help people better understand how to manage the vital natural resource. Jaramillo says, “We have to know what we are doing with our resources.”