This post was originally published on snow.news, my free Substack on snow science and the state of the snowpack.
I’m a big fan of the hydrologic cycle—and diagrams that explain the essence of life on our planet. The water cycle, as it’s also known, drives weather, climate, erosion, and ecosystems, so it lies at the heart of both our modern, daily existence and the deep, geological history of our planet.
I’ve long been fascinated by the fact that the volume of water circulating on today’s Earth is essentially static: it’s basically a closed system. For billions of years, the H2O has been getting recycled through various phases and locations over and over and over.
(Technically speaking, relatively small amounts of water enter and exit the system: water molecules are lost to space when they break up high in the atmosphere; comets and meteorites continue to deliver water from beyond Earth; and geological processes cause water to be created/sequestered through volcanic activity and subduction zones.)
When it came time for me to start my own consulting business in 2014, I chose the name Sea to Snow, in part due to my focus on water issues and the hydrologic cycle, but also to recognize my own migration from a maritime upbringing on Long Island to a more snowy existence in Colorado.
In the spirit of “a picture is worth a thousand words,” I wanted to share some examples of hydrologic cycle graphics that I’ve found helpful in explaining Earth’s water. (If you need a refresher on the terminology, check out the snow-related glossary I recently created for The Water Desk.)
Below are three diagrams illustrating the water cycle, all from the U.S. Geological Survey (click to enlarge).
I also found the simple diagram below from the National Oceanic and Atmospheric Administration and its National Weather Service.
Given the recent cutbacks and deletions at federal science agencies, I can’t promise that these links will continue to work!
Although water covers about 71% percent of the Earth’s surface, it’s a relatively thin layer, and the fraction that’s freshwater is minuscule.
The graphic below visualizes the volume of water on Earth in a series of spheres: the largest one over the United States shows all of the water on, in, and above the Earth; the much smaller sphere over Kentucky represents all of the planet’s liquid freshwater; and the tiny dot around Atlanta is equivalent to the volume of all lakes and rivers.
The two U.S. Geological Survey graphics below explain where Earth’s water resides. Freshwater only accounts for 2.5% of the water on Earth, and about two-thirds of that is locked up in glaciers and ice caps—at least for now!—while about 30% is groundwater. Surface freshwater is also dominated by ground ice and permafrost—yet another reminder of the significance of the cryosphere.
