Connecting Rivers and Mountains

April 27, 2023

By: Anneka Williams 

As a scientist, I study how climate change is impacting high-altitude and high-latitude ecosystems. I’ve conducted fieldwork in far-flung, remote places including the Alaskan tundra, the Bhutanese Himalaya, and South American Andes. My work has ranged from focusing on how wildfires impact plant-mediated methane emissions to studying plant succession along altitudinal gradients to considering how global warming will impact high-altitude plants. 

I feel fortunate to have spent a lot of time in big mountain ecosystems learning how they work, exploring how they may change in the future, and just playing around on foot or on skis. But what I’m always struck by is how intimately connected mountains are to other ecosystems. Mountains are not isolated systems, but rather important players in both global and local climate and ecosystem function. So, when thinking about the health of our river systems, it can be important to look to the mountains. 

How does the water cycle actually work?

People often refer to mountains as the water towers of the world. Most major rivers have their sources in the mountains and water derived from mountains is important in supporting domestic irrigation, drinking water sources, industry, and electricity generation. 

Water can be stored in mountains as snow, glacial ice, and lakes but it doesn’t necessarily stay in these forms. As temperatures fluctuate throughout the year, glaciers, ice, and snow held in mountains start to melt. As the water moves downhill in liquid form, it feeds into rivers and lakes and seeps into soil and groundwater sources. In this way, the amount of water stored as snow and ice in mountains has strong implications on river ecosystems because, come springtime, a lot of that water will be transported from the mountains to the surrounding rivers as temperatures rise. 

Once it reaches a river or lake, water will begin to flow through that system. However, some water will also evaporate, turning back into a gaseous form. Evaporation of water from rivers and lakes and transpiration of water from plants transport water from the land back into the atmosphere. Warmer air holds more moisture so when air masses are forced to flow over high topographies (i.e. mountains) they cool and condense meaning they can’t hold as much water vapor. This leads to precipitation over mountainous regions and thus water continuously cycles through different phases and different geographies. 

How is climate change impacting the water cycle?

In the past several decades, we’ve begun to see the effects of anthropogenic activity on climate across different scales. One of the main hallmarks of climate change is more CO2 in the atmosphere which, in turn, drives warmer temperatures. Warmer temperatures mean water evaporates faster from the ocean, lakes, and rivers. In other words, these warmer temperatures speed up the water cycle. Warmer temperatures also mean that the atmosphere can hold more moisture. Faster rates of evaporation combined with a greater capacity of the air to hold water vapor leads to greater rates of precipitation and bigger storm events.

It’s important to note, however, that the impacts of climate change on the water cycle are not evenly distributed. Some areas are becoming more drought-prone as warmer temperatures suck water out of local sources. Other areas are on the receiving end of heavier and more frequent storms, making these locales at greater risk of flooding. As anthropogenic climate change accelerates, these trends are only expected to become more pronounced and, already, are posing threats to human health and livelihood. 

What does all of this mean for the Colorado River basin?

The Colorado River basin relies heavily on snowpack in the surrounding mountains of Colorado and Wyoming for its water source. And how precipitation falls (i.e. as snow or rain) in the mountains matters. In this region, the proportion of precipitation that is falling as rain, not snow is increasing as temperatures rise. Because rain runs off more quickly than snow, it moves through the river system more quickly, providing less long-term security in terms of water supply. This region is also experiencing less snowpack and earlier melt, which further undermines the water supply to the Colorado River basin. 

Not only are the mountains that feed the Colorado River basin getting less snow and more rain and depleting the river, but the basin itself is also experiencing greater rates of evaporation due to warming temperatures. This leads to more water loss as water evaporates into the atmosphere and is transported elsewhere. 

The dynamics of climate change are complex and vary between regions but, when it comes to watersheds, it’s important to consider the role of mountains. Thinking about the health of the Colorado River basin each year requires us to consider what happens in the surrounding mountains during the winter: how much precipitation falls as snow versus rain? What is the extent of the snowpack? Are there freeze-thaw cycles? How cold are the temperatures? In this way, mountains serve as important indicators for watershed health. 

Anneka Williams is a writer and climate scientist originally from Vermont’s Mad River Valley. Anneka grew up roaming around New England’s trails and trying to keep up with the “big kids” on ski lines at Mad River. She has since pursued adventures and work all over the world, including the mountains of Chilean Patagonia, the Bhutanese Himalaya, the streets of Copenhagen, the trails of the French Alps, the Alaskan tundra, and the Andean paramo. When she’s not writing, Anneka can usually be found backcountry skiing, trail running, rock climbing, or snacking on chocolate-covered espresso beans somewhere in the mountains. Her writing can be found at: www.annekawilliams.com.