The Earth Story

Poor snow person

This video comes from a just-published paper studying the dynamics of avalanches using detailed computer simulations of the physics of the snow. Turns out that, according to the authors, they started with code that was written by Disney for use in simulating snow for the movie Frozen, so this is science with an assist from Disney.

The code wasn’t written to analyze the science, just to make the snow look good on screen. The code simulated the snow as single elements that could move and interact independently, and included some basic details like gravity to make it look realistic. To make it applicable to science, researchers led by a scientist at the Swiss Federal Institute of Technology started building in other properties of snowpacks, such as the porosity of different layers and how the particles of snow bind together.

It is well established that many large avalanches start when there is a weak layer in the snow. Early season snow often falls on warm ground and partially melts before it is chilled and buried later in the season. This process creates an unstable situation where there is a porous, weak layer at depth buried beneath large amounts of snow. Scientists have simulated how that weak layer can collapse and trigger an avalanche before, but they haven’t been able to get the mechanisms to work right. In other words, they can simulate that an avalanche happens, but they couldn't make reasonable models for how big it would be.

The newly built code takes into account more of the interactions between the ice particles and the air – how they deform when they respond to stress, how the deformation mechanisms change when motion begins, etc. The end result is simulations like this one, starting with the small snow person trigger and ending with a full avalanche simulation. Using this model, scientists could go to real areas where avalanches are possible, collect data on the snowpack and the topography, and begin to actually assess the sizes of avalanches that could occur as the season develops.

-JBB

Video credit and original paper: https://www.nature.com/articles/s41467-018-05181-w

Reference: https://www.wired.com/story/a-mind-bending-avalanche-animation/

Declining snow cover in the Rocky Mountains

Over 70 million people in the United States rely on the winter snows in the Rocky Mountains. The water trapped in that snowpack travels down the rivers in the Western U.S. every year, filling reservoirs, irrigation channels, and the pipes leading to homes.

This image shows a portion of the Rocky Mountain snowpack towards the end of the winter. Thick piles of snow, starting to turn darker colors from dust and the beginning of melting.

It’s been known for a while that the snowpack in the Rockies has become less consistent over the last few decades. Here at TES, we recently covered the emptying of Lake Powell, one of the main man-made reservoirs on the Colorado River (http://tinyurl.com/p3a3bdv). Thanks to new research, some of the causes of the declining water supply and declining snowpack can be better understood.

A recent study led by researchers from the US Geological Survey and published in the journal Geophysical Research Letters looked at measurements of the Rocky Mountain snowpack going back over a century. They looked at precipitation variations and temperature fluctuations, and found a few noteworthy trends.

First, the 1930’s “Dust Bowl” era stood out as having particularly low precipitation compared to any of the other periods they looked at.

Second, in the other decades, they found there was an oscillating pattern; in some years the northern part of the snowpack would melt early, in other years the southern part would, with the timing driven by local weather variations.

But finally, everything changed starting in 1980. After 1980, both the sections of the snowpack they looked at started melting earlier and earlier in the year. At this point, the early melting has accounted for a 20% decrease in the total snowpack cover in an average year, and this warming trend has begun completely dominating the variation observed in previous years.

This snowpack decrease is really bad for the people who rely on it as a water source. Melting earlier in the season means that there is longer for evaporation to take place and longer for plants to grow, using up that water before the manmade systems can harvest it. It also leads to more intense fire seasons, because plants grow earlier in the year and have longer to dry out.

Tens of millions of people and billions of dollars of industry and agriculture rely on the supply of water from these snowpacks. But, as the climate warms, the water supply that supports the Western U.S. is becoming increasingly tenuous.

-JBB

Full study: http://onlinelibrary.wiley.com/doi/10.1002/grl.50424/abstract

USGS Press release: http://www.usgs.gov/newsroom/article.asp?ID=3587&from=rss_home#.UZY9f8pHPDV

Image credit: T. H. Painter, Snow Optics Laboratory, JPL/Caltech http://www.nasa.gov/topics/earth/features/snow-patrol.html

Rutgers University Global Snow Lab: http://climate.rutgers.edu/snowcover/

Ah spring

In the northern hemisphere, the cold has broken, the snow is melting, baseball season is around the corner, and I just walked to class without a jacket. Here, take a look; you can even see the mighty granite monoliths of Yosemite National Park as the year’s snowfall retreats away.

Wait, what are the numbers on there? You mean these photos don’t show a single season, they show…oh wait this is really bad.

These photos were taken from a webcam operated by the Yosemite Conservancy on March 19th of each year since 2011. You can see easily how the snowpack in the park goes from normal/almost normal to…well, what snow?

California survives every year in large part thanks to the water stored in the snowpack. Dams hold it and aqueducts carry it around the state for both agriculture and drinking water. These images are a stark note of how extreme the state’s drought conditions are.

The state’s snowpack as of April 1 is at 8% of normal after several years of intense drought. April 1 is important because it’s generally the end of the wet season, to be followed by the dry season and the fire season. If the water isn’t there now, it’s not likely to come this summer.

The other amazing recent statement about this drought is that the reservoirs in California currently only hold 1 year’s supply of water. That doesn’t mean California will run out of water in 1 year – if it rains next winter it will boost supplies and some of the demand can be offset by groundwater usage and conservation efforts, but the state of California is rapidly running out of water. They may not run fully out of water next year, but if this drought doesn’t break next winter, running out of water entirely in the state’s reservoirs could look likely.

A major urban area, or even several major urban areas not having enough water to satisfy demand is something the United States hasn’t seen in recent memory, and this state is getting perilously close to showing us what that is like.

Image credit: NWS Hanford http://twitter.com/NWSHanford/status/580760355493650433/photo/1

Read more: http://bit.ly/19BMpHP

http://lat.ms/1x8xzUk

Deepening drought

In December, California was hit by an “atmospheric river” event, a storm fed by a stream of moisture directly from the tropics. That storm dumped several centimeters of rain on the entire state over a period of several days, offering some hope that the long drought in the state might be coming to an end.

Unfortunately, January has been much the same as the last year, another month missing the rain. January is on track to be a record dry month for many areas of the state, leading to further depletion of the mountain snowpack that the entire state relies upon for its water supplies during dry seasons. In San Francisco, January 2015 is the first January since records began in 1850 with absolutely 0 rainfall at the official recording station at the airport.

Hope for an El Niño event that could have signaled a break in the drought has faded and the state seems en route to yet another record-dry winter despite the early-season rain. On top of the depletion of water supplies in California, the drought is impacting other areas, with snowpacks in Arizona below average and the demand from California beginning to wear down the supplies of other neighboring states.

-JBB

Image credit: LA Times Graphics http://lat.ms/1GtIYQ3

Read more: http://slate.me/1yGfvL1 http://bit.ly/1LxaMFQ http://tmblr.co/Zyv2Js_P34XM

Frozen rivers and climate change

These two images capture an annual event that has either occurred or is just about to occur on most rivers in the far northern reaches of the world. In the lower image at the bottom right you can see a sheet of ice in the delta of the MacKenzie River; the longest river in Canada. In the upper frame, taken one day later, that ice has shattered and ice floes are heading out to sea.

The breakup of the ice is a single event that can be timed every year, and as the climate has changed the ice breakup has shifted dramatically. On average today it occurs more than 10 days earlier in the year than it did only a few decades ago.

To understand these changes, Simon Fraser University scientist Lance Lesack has been studying how the ice breakup relates to other weather patterns in the area, and it’s actually been quite confusing. For example, winter temperatures in the delta have warmed by 5.3°C on average, but the correlation has been poor. Despite that huge change in winter temperature, the hottest winters have not led to the earliest breakups.

Instead, Dr. Lesack found something fascinating that did correlate with ice breakups. Spring temperatures in the area have increased only by 3.2°C, but those spring temperatures correlate strongly with the ice breakup dates. How could the big changes in winter temperatures not matter but smaller changes in the spring be so important?

It turns out there was one more key point; snowpack. As the winter temperatures have warmed, the area on the whole has received much less snow; today there is almost 50% less snow sitting on the ice than there was a few years ago. That snow insulates the ice; if the snowpack was still thick, then the spring temperatures wouldn’t matter as much.

Instead, once the snow is gone, suddenly all that matters for the breakup is when the temperatures cross a threshold. Once it gets just warm enough in the spring, the ice cracks and the river breaks loose.

There are few detailed measurements of snowpack thickness in the Arctic. Dr. Lesack was only able to get measurements of snow thickness in this area since the 1950’s thanks to direct measurements at the town of Inuvik. This study highlights how sensitive the climate system can be to changes in only 1 or 2 unexpected variables; the biggest temperature change wasn’t directly important, but big changes in snowpack combined with small changes in springtime temperatures led to a big change in the river’s behavior.

To understand complex systems like this and how they will react in a warming world, it’s not going to be sufficient just to measure the air temperature. The stability of ice throughout the world is going to be impacted by properties like the thickness of snowpack during the winter that we’re only beginning to figure out ways to measure.

-JBB

Image credit: Simon Fraser University, reproduced with permission https://www.flickr.com/photos/sfupamr/13586973483/in/set-72157643321328673

Original paper: http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2013GL058761/

Press release: http://www.redorbit.com/news/science/1113113027/twist-on-arctic-melt-revealed-by-river-ice-040414/

California declares drought emergency On Friday, during a visit to San Francisco, Governor Jerry Brown officially declared the state of California to be in an emergency drought situation. That declaration is necessary to begin sending government aid to farmers and potentially to enforce water use restrictions across the state. Much of California is quite dry, receiving rainfall amounts comparable to deserts. The Sierra Nevada mountain range, which runs north-south through the state, supplies much of the state’s water through yearly snowfall which melts in the spring and feeds reservoirs, rivers, lakes, and aqueducts that sustain the cities and agriculture downstream. Right now, mountain snowpacks are, on average, at about 20% of their normal levels for this time of year. Significant portions of the state have been in drought conditions since 2012, but 2013 was likely the driest year on record for the state. Since early 2013, over 80% of the state has been consistently in severe to exceptional drought conditions. In fact, as shown in this photo from December, the Folsom reservoir near Sacramento has dropped in volume so much that the remnants of a gold-rush era settlement are emerging from the lake. Normally the winter is the wet season in California, but even now, the Los Angeles area is under severe fire conditions and suffered several days of fire and poor breathing conditions last week. California’s multi-billion dollar agriculture industry and tens of millions of people rely on the state’s water supplies, and right now the rains simply aren’t there. The state has begun requesting people attempt to cut their water usage by 20%, but if things don’t improve, that will be a very tiny first step. -JBB Image credit: Folsom Telegraph http://www.folsomtelegraph.com/photos/under-lake-december-2013 http://sanfrancisco.cbslocal.com/2014/01/17/governor-brown-makes-drought-official-in-sf-appearance/ http://www.nytimes.com/2014/01/18/us/as-californias-drought-deepens-a-sense-of-dread-grows.html