Water forecasting could be thrown off by a changing climate. Credit: Craig Miller

The severe flooding on the Mississippi River has left a lot of damage in its wake. It's an extreme event that government and insurance companies try to plan for by predicting the risk. But climate change is throwing a wrench in those calculations.

Most of us don't think about risk. We think about randomness. That's illustrated by a scene in the 1982 movie, "The World According to Garp", where Robin Williams is shopping for a new house with his wife. They're standing in front of one home when…a plane crashes into it.

Despite the crash, the Robin Williams character agrees to buy the house saying, "It's been pre-disastered! We'll be safe here."

That may not be a typical reaction, but climatologist Kelly Redmond says it reveals a lot about how we think about risk. "It has to do with how we describe rare things. We spend societally an enormous amount of resources and time and attention guarding against the very worst possibilities."

Listen to the QUEST radio story Insuring for Extreme Weather

You've probably heard of the "100-year flood." That's a flood so severe that it has a one in one hundred chance of happening every year. But how do we know that?

"About the only way we can get at how rare a rare thing is is by looking at a past record," says Redmond. So for floods, government agencies look into the historical record to see when floods happened in the past. They use that record to predict future flood risk.

But this relies on a very basic assumption. According to Redmond, the assumption is that the statistics of the future will look like the statistics of the past.

There's a fancy term for this – it's called stationarity. But there's a problem.

"What we don't know but what we suspect with changes in climate is that those statistics, especially about rare things, may change," says Redmond.

The US is already warming. Climate models show that western states could see more extreme weather as the climate continues to change. So, Redmond says, chances are good the future won't look like the recent past.

Jeanine Jones of the California Department Water of Resources agrees, saying "a lot of California's existing infrastructure was designed on assumptions that are no longer valid."

History of Water Forecasting in the West

Jones says using the past as a guide for the future is a huge part of water planning and building codes. The idea was first adopted in the 1940s and 50s, when dams and infrastructure were built at record speed in western states.

"Congress was looking at all these water development plans coming in from the Corps of Engineers and the Bureau of Reclamation and wanting a common standard to compare all the projects," says Jones.

So they forecasted flood risk and water supply by looking at historical data. "But they had very short data records. Maybe they only measured records of 20 years, 50 years. And that's not really very long," Jones says.

Today, everything from building codes to home insurance is based on this short window of data. And so is another critical forecast.

During the winter, surveyors measure the Sierra Nevada snow pack every month, so they can crunch the numbers and predict the year's water supply.

"It is very widely used by reservoir operators, by water agencies, by farmers who are looking at what are my chances for having a full water supply," says Jones.

But climate models show that more precipitation will fall as rain in California, instead of snow. And that means spring runoff could behave very differently. "At some point, conditions will change enough that we've reached a tipping point where those statistical approaches really aren't valid anymore," Jones says.

An accurate water forecast is crucial to California's economy. So Jones says water officials are looking at using computer models to forecast spring runoff.

But when it comes to updating flood risk and building codes to reflect climate change, Kelly Redmond says that could take decades. "We have to get a buy in from the engineering community, the city planners. Because there's so much expense to goes into building a bridge or a culvert or a building."

A New Breed of Insurance Company

There is one industry that's taking note of climate change – insurance.

"The increased variability in climate is going to start to dramatically affect the profits of corporations worldwide," says David Friedberg, CEO of San Francisco-based Weatherbill.

Weatherbill is something of a next generation insurance company. They start with computer models that simulate weather and climate patterns. "We then use those sorts of models to determine what sort of price we should charge for certain weather events occurring," says Friedberg.

Weatherbill works mostly with farmers, insuring them against extreme weather for between 40 and 400 dollars an acre. "There's a range of things that can occur and that range is certainly widening. And as a result we should start to charge more for those sorts of events when we're insuring them."

Friedberg says this kind of insurance makes sense to a lot of farmers they work with, who are already noticing changing weather patterns. Investor Vinod Kholsa and Google have also noticed and put millions into the company. They're betting new software will be the answer when today's methods no longer work.

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It's been a harsh winter across the US. Snow has blanketed the Sierra Nevada, where the snowpack is well above normal. Lots of snow means good skiing, but it also means an increased danger of avalanches.

Avalanches aren't something most skiers and snowboarders have to think about. That's because ski areas take preventative action.

On the backside of Squaw Valley Ski Resort, two ski patrollers drop into a black diamond run known as Granite Chief. Below them are mounds of fresh, untouched powder – more than seven feet deep.

The patrollers are throwing explosive charges onto the slopes to trigger smaller, less dangerous avalanches. Booms ring out across the mountain.

Listen to the QUEST radio story The Science of Snow

"The Sierras are known for getting tons of snow really quick," says Will Paden, the avalanche forecaster at Squaw Valley Ski Resort. "We're constantly trying to start the avalanches so that we don't let the snow pack build up to be too deep."

Paden says on a day like today, they'll use more than a thousand pounds of explosives to make the ski area safe. But the job isn't over when the snow stops falling. The snowpack is constantly changing.

"One day could be perfect powder and then that afternoon the wind can pick up and put wind crust on top of that perfect powder and make it difficult skiing," says Paden.

Avalanche forecasting is even more technical. "We had a lot of riming in this snow and some graupel events."

To translate that, you have to go inside the snowpack.

On a slope outside of Truckee, Brandon Schwartz uses a shovel to cut a cross-section in the snow. As a forecaster with the non-profit Sierra Avalanche Center, Schwartz has dug thousands of avalanche pits like this one.

An avalanche near Echo Summit in Lake Tahoe.
Credit: Travis Feist"We can feel the different hardness of all the layers that have formed in the snow that's fallen over the last two to three days," says Schwartz.

Schwartz is looking for weak layers of snow, which is where avalanches begin. He pulls out a saw and slices through the snow to isolate a one foot wide column. Then he places his shovel on top. "And we'll just start to load on top of it first with ten taps just from my wrist, just from lifting my wrist and letting gravity pull my hand down."

Those taps simulate what a little weight would do to the snowpack, either from more snow falling or from a skier.

Schwartz points to where the snowpack has broken away along a straight line. "So we got a pretty significant crack all the way across the column here. Definitely a difference in strength there and that's what makes up the layers of snow pack and when we have these layers of different characteristics then we start to get some of the ingredients for a slab avalanche."

Schwartz and his team travel into the backcountry every day to assess the avalanche danger in the Tahoe region. Of the 36 people who died in avalanches across the United States last winter, almost all of them were in the backcountry. A large storm like this one means today the danger is high.

But what makes some snow weaker than other snow?

"Once we have snow on the ground, a whole bunch of really interesting things happen. You think of the snow as being rather static, but it's not at all," says Jeff Dozier, an environmental scientist at the University of California-Santa Barbara who studies how snow impacts California's water supply.

Dozier says to understand what's happening, you have go all the way down to the level of a snowflake.

Check out the different types of snow crystals, as seen under an electron microscope:

Once the snow falls, the snow crystals will start to stick together. As they sit there, the crystals grow rounder and bond together. "And if you shovel snow, you see this. If you shovel snow when it's new, you can stick the shovel in the snow and you can lift it. You shovel snow when it's old, it's hard to break that block of snow loose from its neighbor."

When a lot of snow falls quickly like it does in the Sierras, this bonding process may not happen fast enough to support the snowpack, which leads to avalanches. The warmer a snowpack is, the faster it bonds. But if it's colder, sometimes a different kind of crystal grows.

"Typically the temperature at the base of the snowpack – this is gonna be around zero degrees C. But on a very cold night, the temperature at the surface say might be -20 degrees C," says Dozier.

That difference in temperature can create another shape of crystal – a faceted crystal. "They're sort of angular. They don't bond together very well."

These crystals look like grains of sugar and they create weak layers deep in the snowpack. A better understanding of snow crystals could help avalanche forecasters. Dozier says it could also help water managers trying to anticipate the snowpack melt in the spring, an event that's critical to the state's water supply.

Avalanche forecaster Brandon Schwartz in the field:

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Kirkwood Mountain Resort.

It's that time of year when people head up to the Sierra Nevada Mountains for some great skiing and snowboarding. This season is looking to be a good one with a handful of big storms dumping huge amounts of snow on resorts and in back-country terrain. Although deep snow cover obscures the view of some of the geology, the views from chair lifts and other vistas while skiing is a fantastic opportunity to think about the geologic evolution of these mountains.

My favorite ski area in the Sierra is Kirkwood Mountain Resort, which is along State Route 88 approximately three to three and a half hour drive from San Francisco and 20-30 minutes from the town of South Lake Tahoe. In addition to great terrain, Kirkwood has some fantastic geology, some of which you can ski right up to and check out in detail.

The rocks exposed at the surface on the mountains of Kirkwood are various volcanic rocks ranging from about 6 million to 15 million years old (depending on exactly where you are). The volcanic deposits at Kirkwood are nothing like the smooth lava flows you might see on the Big Island of Hawai'i. They are more similar to the recent volcanic deposits seen on the flanks of and in areas adjacent to the Cascades volcanoes in northern California, Oregon, and Washington.

Many of the cliffs exposed at Kirkwood during the winter are beautiful volcanic debris flow deposits that have up to boulder-sized chunks of igneous rock within a fine-grained rock. These rocks are interpreted to be the deposits of mixtures of mud, sand, and volcanic rock debris that flowed down the flanks of the now-extinct volcanoes. I forgot the name of the specific trail — please comment if you know — but there is a great run where you can take a short break to catch your breath and walk up to some outcrops of these debris flow deposits.

So, next time you're sitting on the chair lift waiting to take that next run, look around at these beautiful mountains and picture the ancient volcanic landscape that created the terrain you're skiing.

Images: (1) Kirkwood from Mal Parkington / Flickr; (2) Glove Rock from Dean_In_SF / Flickr

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Satellite image of the western United States, taken on Thanksgiving Day. Image: NASA.

The defining sign of a La Niña is cooler-than-average sea surface temperatures in the Pacific Ocean, near the equator. Cooler water evaporates less than warmer water, so there is less moisture in the air. This means that during a La Niña, there is less precipitation in some areas, like California and the southern United States. Other areas, like the Pacific Northwest, get more precipitation during a La Niña. (Book your winter ski trip strategically!)

Sea surface temperature anomalies on November 25, 2010. The equatorial Pacific is cooler than usual (note the blue color), a characteristic of a La Nina event. Image: NOAA.La Niña also affects air temperature. During a La Niña, the South is typically warmer, while Southern California and the Pacific Northwest are cooler. You can see climate predictions for the next three months, from the National Weather Service Climate Prediction Center.

A La Niña is basically the opposite of an El Niño. El Niños are characterized by warmer-than-average sea surface temperatures in the equatorial Pacific. This happens when the atmospheric pressure system gets a bit out of whack. Usually there is high pressure over the Pacific Ocean and low pressure over the Indian Ocean—picture a see-saw anchored over New Zealand, with the heavy kid sitting on the end over Indonesia. For reasons we don’t quite understand, sometimes the see-saw tilts the other way—now the heavy kid is sitting in the southeastern Pacific, and the kid on the Indonesian side is way up in the air.

This swap in atmospheric pressure has quite a few consequences. The trade winds (which typically blow across the Pacific from the east to the west) get weaker. The water that the trade winds usually push westward instead piles up and moves east. This water is warm, and it evaporates, causing more rainfall along the west coast of South America. Meanwhile, places like Indonesia and Australia get less rainfall, along with drought and fire.

The weakening of the trade winds and westward flow of ocean currents in the Pacific has a second effect. Under non-El Niño circumstances, the trade winds carry the top layer of water to the west, and so water from deeper in the ocean moves up to take its place. This is called upwelling. The water from deep in the ocean is cold and full of nutrients, and it drives the fisheries along the coast of Chile and Peru. Without the trade winds and the upwelling, fisheries crash. A strong El Niño has big economic impacts, not all of which are negative; some agricultural areas are benefited by the extra rainfall, and people in places with unusually warm weather can save on heating bills. Of course, La Niña events have economic impacts too.

As scientists learn more about predicting the climate during El Niños and La Niñas, we can plan accordingly and mitigate the economic impacts of these events. My comment about planning your ski vacation according to this year’s La Niña was a little bit serious! Rainfall predictions based on El Niño and La Niña models can help farmers decide which crops to plant. And, here in drought-prone California, La Niña precipitation predictions are influencing water allocation decisions for the coming year.

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Terrestrial snow at Chabot on December 16, 2008
Photo by Craig Coryell

This is quite unusual for the Oakland Hills, of course. In the ten years I've worked here, this is the second, maybe third, dusting I've witnessed. I recall the great freeze of '74, when it actually snowed in Oakland close to sea level—that's the year all the eucalyptus in the hills froze and died.

My mind wandered—pretty far out in space (an occupational hazard at Chabot). I started thinking about all the recent news and discoveries from around the Solar System, my thoughts guided by the fat white flakes drifting down all around the observatory domes.

Last September, NASA's Mars Phoenix Lander detected snow falling high in the atmosphere–about 4 kilometers high. This Martian snow, however, quickly evaporated in Mars' thin, dry air, never reaching the ground. Phoenix used a laser probe to make the detection–so we don't actually have picture to look at!

Snows of the Solar System may also fall out of the plumes of "cryovolcanoes"–the frigid outer Solar System's version of volcanism (may it live long and prosper). On moons such as Saturn's Enceladus and Neptune's Triton, plumes of material have been detected spouting from fissures and cracks–probably fueled by heat generated by tidal forces from their parent planets.

On Enceladus, the geyser plumes contain water vapor and ice crystals, and are believed to come from subsurface lakes of "warm" water (32 degrees Fahrenheit–in other words, ice water… but that's a veritable hot spring, or magma chamber, on a cold moon like Enceladus!).

The ice crystals in the geysers' plumes mostly fall back to Enceladus–maybe in a diffuse fall of "snow" across the globe? I'm waiting for those pictures…

Saturn's large moon Titan is speculated to possibly have a form of cryvolcanism, though no direct detection has yet been made. Still, any water vapor that might erupt from a Titanian cryovolcano might be expected to fall in a form of snow….

Triton, much farther from the Sun than Saturn, is even colder than Enceladus. In fact, it's been called the coldest measured surface in the Solar System, at -391 degrees Fahrenheit. Here, nitrogen freezes solid. Triton cryovolcanoes, or geysers, may be partially solar-heated, but tidal heating within Triton is probably dominant. Triton's geysers spout nitrogen gas and dark material, which falls across the landscape in dark streaks and lighter deposits of frozen nitrogen–a form of extreme cryo-snow, to my imagination!

Now, are you as cold as I am just thinking about it? Time for a cup of cocoa…

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