No. Hemisphere snowpack likely to shrink faster than previously thought
Written byANNE C. MULKERN, ClimateWire
Rising global temperatures are likely to shrink snowpacks in the Northern Hemisphere aggressively and sooner than previously thought, with some changes coming in the next 30 years, a new study out of Stanford University says.
It would have major implications for water supplies that are used for drinking, agriculture and in some places hydropowered-electricity, experts said. It is also likely to affect the ability to control floods, as snowpack that melts earlier in the year increases downhill runoff. There could also be more rain versus precipitation stored on the mountains through the winter as snow.
That would affect how much water is available in spring and summer, potentially increasing how often very dry years occur.
"While reduced snowpack has been predicted for some time, they find that the shift toward low snow years and increasing water stress in the Northern Hemisphere is 'imminent,'" said Andrew Fahlund, executive director of the Water in the West program at Stanford. "Essentially, they are showing that what we have come to know as 'low water years' in the past are going to become the new normal in fairly short order.
"What we've come to know as 'extreme drought' years -- relatively rare in the time that the western U.S. has developed -- are going to become more common," Fahlund added.
The research, published Sunday in the journal Nature Climate Change, synthesized data from 55 climate model simulations that have recently become available. The study looked at how warming will affect snowpack in the western United States, Alpine Europe, Central Asia and downstream of the Himalayas and Tibetan Plateau. More than 50 percent of the world's population lives in those places, Stanford said.
Major impact on West Coast
The western United States and Canada, South Asia and parts of north and central Eurasia will be the most affected, said lead author Noah Diffenbaugh, an assistant professor at Stanford and a fellow at the school's Woods Institute for the Environment.
The study examined what is likely to be seen in terms of precipitation, snowpack accumulation and water runoff over the next century, versus the same data for the years from 1976 and 2005. It compared the future to the lowest snowpack year seen over that recent 30-year span.
"We've looked at the extremes of snow accumulation and melt," Diffenbaugh said. "If we look at the lowest spring runoff that occurred over late 20th century, how often do we expect to see values lower than that" in the future?
For western North America over the next three decades, 10 to 30 percent of years will have spring snowmelt runoff amounts below those in the worst year seen between 1976 and 2005, Diffenbaugh said.
By the end of the 21st century, he said, the proportion of years with runoff totals beneath the lowest point for roughly the last 30 years could reach more than 80 percent.
Changes come even with lower warming
What was most surprising, Diffenbaugh said, is that the accelerated melting of the snowpack would occur even if the world were able to limit warming to the target of a 2-degree-Celsius increase agreed upon in international climate negotiations in Copenhagen, Denmark.
At that temperature, in western North America, between 10 and 30 percent of years would see that spring snow amount lower than the driest period over the last 30 years, Diffenbaugh said.
"To see very large increases in extremely low snow years within the occurrence of that [Copenhagen] target suggests that there could be substantial impacts from climate change even if that global warming target is achieved," Diffenbaugh said. "The lowest [snow year] in the recent past occurring about a third of the time in the near future, that's a substantial change in the occurrence of extremely low snow conditions."
At a climb of 4 degrees Celsius, the occurrence of low snow years is much more frequent "at 30, even up to 90 percent of the years have spring snow total that's lower than the lowest of the late 20th century," he said.
The study also looked at the amount of snowpack runoff during the warmer season, compared to what has been seen in the past. It forecasts an increase in number of years that have "extremely high melt" earlier than the past, Diffenbaugh said.
Stanford studied the amount of snow in March, considered the end of the snow season. Lower amounts in that month could come as a result of a decrease in the amount of snow, he said, because precipitation will come as rain instead of snow. There could also be less precipitation overall because of warming, or because what falls as snow melts earlier, so that by spring, there is less snow on the ground.
While there is uncertainty about the amount of precipitation in the future, he said, "even if precipitation increases, the increase in temperature is great enough to cause earlier melt to occur," Diffenbaugh said.
That will affect how the western United States handles water, said Fahlund with Stanford's Water in the West program. Right now, places like California assume water will be stored as snow in the winter and then will come as runoff in the spring, which the state apportions for various uses during the dry season. The Stanford study suggests that is going to change, he said.
More storage may be needed
Planning needs to begin now for the adjustments that will need to take place with dams, reservoirs and other water system infrastructure, Fahlund said. Dams, for example, might not be able to hold the amount of water that will come earlier in the year.
"We need to look at the changes in total precipitation and the timing and distribution of run-off patterns and see how that lines up with our current infrastructure," Fahlund said in an email. "We continue to operate those systems using assumptions (called rule curves) that are based on the past and not this new normal.
"We can then get a sense of where and how our current infrastructure comes up short," he added. "Some agencies are starting to do this but are probably not moving fast enough. Since it takes a decade or more to build infrastructure, we have time to react, but not a lot."
Current infrastructure was built for a snowpack and water runoff system that the study predicts won't exist in the years to come, he said. "We have to rethink what sort of infrastructure we build in the future," Fahlund said. "It probably shouldn't look like what we've built in the past."
The first step should be to reduce demand and become more efficient, he said. There also should be consideration of "alternative sources" such as water recycling. Additionally, he said, "we should be exploring ways to store excess run-off in groundwater aquifers so that we can use that water during dry years for human and environmental needs."
Many part of the world get through dry years by "mining" groundwater, he said "taking more out than is ever replenished. We need to dramatically change that approach so that we're actively and passively putting more back in than we take out, over a ten-year-average.
"And of course, flood infrastructure will also need to change and improve, starting with providing incentives or requirements for people to move out of harm's way (floodplains)," Fahlund said.
And it's not just about infrastructure, he pointed out. "We have to also amend our policies, regulations, institutions, and financial mechanisms to adapt to this new normal," Fahlund added. "That's a lot of change in a short time and our track record is that we don't often change those things until the crisis is upon us or has even washed over us. Doing it in anticipation is not what we're good at.
"Finding the money in hard times with lots of competition for resources, is also going to be challenging," he said, "but we must."