Vanessa Abrahamson Blog: Soil moisture up in Colorado, easing drought concerns a bit

Denver Water field crews measure how much water is frozen in the snow near Winter Park on March 29. The utility’s teams take these kind of measurements at 13 sites every month during the winter and early spring. Photo credit: Denver Water.

Water news seems dreadful these days, with a megadrought in the Colorado River Basin, hydropower at risk in a fast-draining Lake Powell and a warming climate assuring these issues will only get worse.

So, amid these calamities, Denver Water wants to cite a small measure of good news: Soil moisture levels in parts of Colorado have improved.

Yes, this may only be a temporary blip on a downhill slide, but let’s celebrate what we can.

Soil moisture is a key indicator of drought conditions and has a big impact on water supplies. That’s because dry, thirsty soils can drink up a lot of the snowmelt that otherwise would flow into rivers and reservoirs.

Know your snowpack: 9 facts about Colorado’s snowpack.

Here’s an example from Denver Water’s own system: In 2021, snowpack above Dillon Reservoir peaked at 88% of normal. It wasn’t a banner year for snowpack, but it wasn’t terrible either. But dry soils made the lower snowpack levels far worse — runoff was only 57% of normal.

“The low soil moisture soaked up a lot of the melting snow before it reached rivers and reservoirs,” explained Nathan Elder, water supply manager for Denver Water.

The 2019-20 water year told a similar story, when snowpack peaked at 124% in the South Platte Basin but runoff came in at just 54% of average at one key measuring point.

Low soil moisture can soak up snow runoff, leaving less for rivers and reservoirs. Image credit: Denver Water.

A similar pattern also cut into runoff in 2018.

This year, water forecasters expect a better scenario. That’s because a big monsoon season on the West Slope and in the mountains last summer brought soil moisture levels up. Snowstorms on the Front Range throughout the winter helped soils here, too.

“This year, with soil moisture better, we are expecting more runoff from the snowpack,” Elder said.

Nathan Elder, water supply manager for Denver Water, in April 2019, standing in a snowpit dug to gauge the snow’s temperature, depth, density and how much water it contained. Photo credit: Denver Water.

Currently, snowpack above Dillon is 87% of normal and, because of greater moisture within the soil, streamflow forecasts are higher too — 82% of normal, a big improvement from last year.

Evidence of the improvement in soil moisture comes thanks to data from NOAA, the National Oceanic and Atmospheric Administration, a federal agency that closely tracks such matters.

The numbers can be complicated, but one way to understand the impact of the soil moisture is in what Denver Water’s water supply managers call “runoff efficiency.”

In a year when soil moisture numbers are just slightly below normal — such as this year — you can expect runoff volumes to be 10% to 15% less than the peak snowpack number.

In a year when soil moisture conditions are worse, as we’ve seen in several recent cases, the dry soils can reduce runoff efficiency by 15% to 20%. That can translate to a big cut in water supply.

The U.S. Drought Monitor maps for the end of March 2022 shows a marked improvement compared to recent months. Image credit: U.S. Drought Monitor.

Another key measure comes from the U.S. Drought Monitor map. That map shows the Denver metro area — as well as much of Denver Water’s collection area — in “abnormally dry” conditions. That may sound bad, but it is actually a marked improvement from recent months when much of the state was in various stages of drought.

A year ago, the region’s drought levels ranged from “moderate” to “extreme” drought.

Things can still change, of course.

Should we get a long spell of warm, dry weather this spring, the situation could become worse. But, at this point in early spring, things look a bit better than in recent years.

“We’ll obviously be watching our watersheds and the weather closely,” Elder said. “But we take the good news where we can get it and, at least for the moment, we’re happy to see these conditions.” Get the latest on Colorado Water Trends

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