(CN) – Water is evaporating from the Colorado River Basin faster than rainfall can replenish it, researchers said in a study published Thursday, and the disappearance of seasonal snowpack has also diminished the river’s water supply.
Over 40 million people in seven states depend on the river for their water, as does a multibillion-dollar agricultural industry across the western U.S.
Much of the Colorado River’s supply originates upstream as snowpack, some of which is lost to evaporation or absorption by plants.
But for years, climate change – particularly in the form of increased drought and temperature spikes – has decreased the river’s flow.
Researchers Christopher Milly and Krista Dunne of the U.S. Geological Survey developed a model to examine the sunlight-reflecting effects of snowpacks – known as albedo – and how that effect changes over time as snow disappears.
Bright snow and ice means heat and radiation from the sun are reflected into space, or that the snow has high albedo. Milly and Dunne’s model shows that climate change has exacerbated snow loss in the Colorado River Basin, meaning the basin is absorbing more solar energy.
Solar energy absorption has increased evaporation in the basin, leading to what researchers estimate is a 9.5% reduction in runoff per Celsius degree of warming, according to the study published in the journal Science.
According to the researcher’s model, climate-change-fueled drying in the basin will outpace projected future increases in rainfall in the region.
Their research addresses longstanding questions on the river’s sensitivity to spikes in temperatures, and they say more analysis is needed to determine how climate change will impact future water supplies.
Milly told Courthouse News the processes examined in the study would not be affected by private water collection. He also said improvements in water storage would not reverse dwindling river flow since the issue is with supply, not storage of water.
The river basin supports more than $1 trillion of annual economic activity, which would be severely impacted by any major water shortages.
A 2019 study by Colorado State University projected that the river’s flow could decrease 20% by 2050 and 35% by 2100.
The Trump administration approved a drought contingency plan last year that will keep two key reservoirs, Lakes Powell and Mead, from falling so low they cannot deliver water or produce hydropower.
The plan was negotiated among the seven states that draw water from the Colorado River.