In the midst of an arid summer in the arid West, any amount of rain can feel like a giveaway. But in reality, those precious summer showers barely move the needle when it comes to water.
“No matter what you get in the summer,” said Becky Bolinger, assistant state climatologist for Colorado, “what really impacts water availability in the Colorado River is what happens pass in winter”.
As a drought-stricken region looks to summer, climatologists are monitoring high mountain snow cover and its path to streams and rivers. High-altitude snow makes up the majority of the Colorado River’s water — where last winter left low totals. On top of that, the warm temperatures and dry ground mean the snow is likely to melt early and soak into the ground before it can reach the Colorado River.
Snow in Colorado alone accounts for two-thirds of the water flowing into Lake Powell, one of the most important storage facilities on a river that supplies 40 million people in the Southwest.
Many snow-watching sites in Colorado measured near-normal peaks, but a warm, dry spring pushed snowpack even further below average for this time of year. The high-altitude western slope of the state is about 80% of average in most areas, but southern portions of Colorado have dipped into the teens.
Even in places where snow totals are closer to normal, Bolinger says not all runoff will reach rivers.
“Unfortunately we’ve been dealing with dry soils since the start of the previous season, which means a lot of that is going to be recharging the soils,” she said.
As consecutive dry years begin to accumulate, the soil becomes parched. When the snow melts on top, the ground acts like a spongeabsorbing water on the way down.
On top of that, this year’s snow is melting early. Karl Wetlaufer, assistant supervisor of snow surveys at the Colorado Natural Resources Conservation Service, said this was partly due to windy conditions, which blow dust onto the snow, creating a darker, more heat-absorbing surface. .
“When this dust hits the surface,” he said, “it retains a lot more energy from the sun. So we also saw a dramatic acceleration in snowmelt and runoff resulting from this dust on the mantle. snowy.
Rapid melting is particularly evident in the San Juan Mountains of southwestern Colorado. At a measurement site, snow totals have dropped after peaking near average, melting more than three times faster than normal.
Between the dust, dry ground, and above-normal temperatures forecast for the West, the mountain snow won’t be as helpful as the Colorado River needs it to be.
“It’s going to be many, many years before I think we can get back to some semblance of normality,” Wetlaufer said.
The region is accumulating a reserve of water in reservoirs from Wyoming to Arizona, and these reserves are shrinking as homes and farms continue to draw water. At this rate, snowmelt simply cannot keep up. Lake Powell water levels have dropped to the crisis point. As state and federal agencies work to fill it with stockpiled water from other parts of the basin, it seems unlikely that many reservoirs in the region will see significant filling from snowmelt.
“I would definitely say that this year’s snowpack will not be enough to significantly increase those storage values,” Wetlaufer said.
Hundreds of kilometers downstream, water specialists also put a lot of emphasis on snow. Arizona State climatologist Erinanne Saffel says mountain snow still makes a difference to practices like groundwater replenishment, which Arizona uses to store excess water underground to to protect against a dry future.
Although snow does the heavy lifting in the Colorado River Basin, Saffel said summer precipitation makes a difference in more subtle ways.
“It recharges the cattle ponds for the ranchers,” she said. “That’s the kind of stuff we pay attention to. So when we don’t get that summer precipitation, there are implications.
In the north, near the headwaters of the Colorado River, Becky Bolinger said summer rains are helpful in reducing wildfire risk and keeping soils saturated for the upcoming snow season. Looking ahead, she said the forecast for this summer still stands.
“The big question will be, ‘Will the monsoon come and bring the moisture we need when we need it?'” Bolinger said. long and you need that summer humidity to carry you through the fall, and that’s something that’s really hard to predict.
A seasonal temperature forecast from the National Weather Service shows that areas containing critical snowpack for the Colorado River are most likely higher than normal temperatures this summer. Meanwhile, summer precipitation across much of the Colorado River Basin is should be close to normal.
A magnified view of climate trends in the Colorado River Basin does not paint an optimistic picture for the summers ahead. Hot, dry years have been piling up for more than two decades, and human-caused climate change is making it less and less likely that cool, wet seasons will return significantly.
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