'On a Whole Other Level’ - Rapid snow melt-off in American west stuns scientists.
Experts warned that even as the heat begins to subside, the stunning pace of melt-off over the past month has left key basins in uncharted territory for the dry seasons ahead. Though there’s still potential for more snow in the forecast, experts said it will probably be too little too late.
Acting as a water savings account of sorts, snowpacks are essential to water supply. Measurements taken across the west during the week of 1 April are viewed as important indicators of the peak amounts of water that might melt into reservoirs, rivers and streams and across thirsty landscapes through the summer.
During a critical survey in California’s Sierra Nevada on Wednesday, grass and mud could be seen through the thin white patchwork as state officials attempted to measure the meager snowpack.
“Normally we’d be standing right here,” Andy Reising, manager of California department of water resource’s snow surveys and water supply forecasting unit said, gesturing at chin height. The 5ft-tall tool typically thrust deep into the high berms on 1 April poked into the brown earth next to him. “There is actually no measurable snow.”
With zero depth and zero water content, this year’s annual April snow survey conducted at Phillips Station, was the second worst on record, beaten only by 2015 when officials “walked across a dry field”, Reising said.
It’s not just the amount of snow left on mountaintops that’s concerning experts, but the amount of moisture still frozen within them. “Snow water equivalent” (SWE), a measurement of what could melt off to supply natural and manmade systems, is exceptionally low.
California’s Sierra Nevada had just 4.9in of SWE, or 18% of average on Wednesday, according to the state’s department of water resources.
In the Colorado River headwaters, an important basin that supplies more than 40 million people across several states, along with 5.5m acres of agriculture, 30 tribal nations, and parts of Mexico, had just over 4in of SWE on Monday, or 24% of average. That’s less than half what was previously considered the record low.
Schumacher said the incoming storm could slow the early melting but won’t be enough to pull the basins back from the brink. Snow water equivalent measurements going into April were at levels typically seen in May or June, after months of melt-off, according to Schumacher.
The issue is extremely widespread. Data from a branch of the US Department of Agriculture (USDA), which logs averages based on levels between 1991 and 2020, shows states across the south-west and intermountain west with eye-popping lows. The Great Basin had only 16% of average on Monday and the lower Colorado region, which includes most of Arizona and parts of Nevada, was at 10%. The Rio Grande, which covers parts of New Mexico, Texas and Colorado, was at 8%.
“This year has the potential of being way worse than any of the years we have analogues for in the past,” Schumacher said.
‘Nothing short of shocking’
Even with near-normal precipitation across most of the west, every major river basin across the region was grappling with snow drought when March began, according to federal analysts. Roughly 91% of stations reported below-median snow water equivalent, according to the last federal snow drought update compiled on 8 March. Water managers and climate experts had been hopeful for a March miracle – a strong cold storm that could set the region on the right track. Instead, a blistering heatwave unlike any recorded for this time of year baked the region and spurred a rapid melt-off.
“March is often a big month for snowstorms,” Schumacher said. “Instead of getting snow we would normally expect we got this unprecedented, way-off-the-scale warmth.”
More than 1,500 monthly high temperature records were broken in March and hundreds more tied. The event was “likely among the most statistically anomalous extreme heat events ever observed in the American south-west”, climate scientist Daniel Swain said in an analysis posted this week.
“Beyond the conspicuous ‘weirdness’ of it all,” Swain added, “the most consequential impact of our record-shattering March heat will likely be the decimation of the water year 2025-26 snowpack across nearly all of the American west.” [...]
In the Colorado River Basin, the situation could be even more dire. The two largest reservoirs on the Colorado River are Lake Mead and Lake Powell, which together account for about 90% of storage, are 25% and 33% full accordingly, as of 29 March, and there is little to fill them.
Already officials are in the process of relocating a floating marina on Lake Powell in anticipation of the quickly receding water levels, as experts warn the vital reservoir could drop to the lowest levels recorded since it was filled in the 1960s. If they fall far enough, the system would cease to function altogether. So-called “deadpool” – when water isn’t high enough to pass through the dams, generate hydroelectric power, and be distributed downriver – would be catastrophic.
The Colorado River has been overdrawn for more than a century but rising temperatures and lower precipitation are putting more pressure on the system that depended on by cities, farms, industries and wildlife across the west. The extreme conditions have added more urgency and greater tensions to fraught negotiations over who will bear the brunt of badly needed cuts. Seven states that have blown past two key deadlines are still locked in a stalemate over how the river’s essential resources will be managed through a hotter and drier future.
Already officials are in the process of relocating a floating marina on Lake Powell in anticipation of the quickly receding water levels, as experts warn the vital reservoir could drop to the lowest levels recorded since it was filled in the 1960s. If they fall far enough, the system would cease to function altogether. So-called “deadpool” – when water isn’t high enough to pass through the dams, generate hydroelectric power, and be distributed downriver – would be catastrophic.
The Colorado River has been overdrawn for more than a century but rising temperatures and lower precipitation are putting more pressure on the system that depended on by cities, farms, industries and wildlife across the west. The extreme conditions have added more urgency and greater tensions to fraught negotiations over who will bear the brunt of badly needed cuts. Seven states that have blown past two key deadlines are still locked in a stalemate over how the river’s essential resources will be managed through a hotter and drier future.
by Gabrielle Canon, The Guardian | Read more:
Image: Guardian Design/Nasa Worldview
