NOAA: Warming and extreme dust could advance spring thaw in Upper #ColoradoRiver basin by 6 weeks

Change in snow-all-gone dates by 2050 via NOAA
Change in snow-all-gone dates by 2050 via NOAA

Here’s the article from NOAA:

Models project that extreme dust events combined with global warming could advance the spring thaw in the mountains of the Upper Colorado River Basin by as many as 6 weeks by 2050. The earlier disappearance of snow could amplify water disputes, extend the fire season, and stress aquatic ecosystems.

The maps at right suggest one strategy that water managers in the West could use to lessen the impacts of climate change: reduce blowing dust. Each image shows model projections of how much earlier in the spring the “snow-all-gone” day would arrive by 2050 compared to today based on the same amount of warming but different levels of dust. Positive days (brown) mean the snow disappears earlier in the spring.

The mountain snowpack in the Upper Colorado River Basin is a natural, frozen reservoir that melts its way into streams and rivers throughout late spring and early summer. Some years, huge amounts of dust blow in from the Southwest, dirtying the snow. The darker snow absorbs more sunlight and melts faster than normal. In those years, the spring thaw—marked by the arrival of the “snow-all-gone” date—can arrive more than a month earlier than normal.

If better soil conservation brought dust down to low levels (left-most map), models project that the average snow-all-gone date would increase by fewer than 20 days (lighter browns) for most of the area (this is for a relatively high greenhouse gas emissions scenario). In a few areas, snow might even linger a bit longer (green areas) than it currently does because models also project some localized increases in snowfall in high, cold terrain.

But regular occurrence of extreme dust levels (right-most map)—which researchers modeled after unprecedented dust conditions witnessed in 2009 and 2010—could lead to winter snows disappearing 40 or more days (darkest browns) earlier in the spring than they currently do. Given that the snow-all-gone date already arrives about three weeks earlier than it once did, the change would amount to a roughly nine-week advance in the snow-all-gone date.

The early disappearance of snow could further add to water supply problems in the already over-allocated river, especially in the Upper Colorado River Basin, which lacks the big reservoirs of the Lower Colorado. Earlier arrival of snow-all-gone dates also means a longer dry season, which would increase fire risk and stress aquatic ecosystems.

The Colorado River supplies water to an estimated 40 million people in the United States and Mexico, and it is already the focal point of heated water disputes among cities, farmers, ranchers, and agencies that protect wildlife. Presently, dust has a bigger impact on spring melt than warming. Climate change alone is likely to advance the snow-all-gone date in the Upper Colorado River Basin, but high levels of dust will only make the problem worse.

The new research identifies a risk to water supplies, but suggests an opportunity for adaptation. The high levels of dust blowing out of the Southwest are due to more than a century of inadequate soil conservation in the area’s dry, fragile soils. Restoring landscapes that have been damaged—by grazing, mining, energy exploration and development, farming, and off-road travel—to reduce blowing dust could keep a potentially manageable problem from turning into a major one.

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