Saturday , September 27, 2014 - 3:01 PM
Local researchers are using the history of a hardy native tree to build a vision of Utah’s drought future.
Cities on the Wasatch Front have exploded for decades, and like many urban areas in the West, those growing populations depend on water supply that’s highly variable. Broad interplays between oceans, the atmosphere and land can lead to heavy snowfall that fills reservoirs. It can also mean long dry spells and looming water shortages.
“Utah is affected by many climate drivers,” said Matt Bekker, a geography professor at Brigham Young University. “So even though we’re dependent on stream flow from snowpack, we don’t have a good idea of what’s coming this winter.”
To better understand these past global interactions and use that information to predict future drought, scientists have increasingly turned to the year-by-year climate record contained in tree rings. This year, Bekker found an especially useful climate oracle in the Utah juniper.
“Utah juniper has a particular water use strategy that makes it very sensitive to variations in moisture,” he said. “When it’s dry the rings are really small and when it’s wet, the rings are really big.”
Bekker has used tree rings as clue’s to Utah’s climate past for years. In 2008, he looked at wood collected during the Salt Lake Tabernacle renovation and found Mormon pioneers arrived during a particularly harsh drought in the Salt Lake Valley. Last spring, Bekker published a paper reconstructing Weber River flows back 576 years using ring data from local Douglas fir and pines.
Utah junipers, however, give him a better idea of what historic wet and dry years looked like. They also allow him to look back further in time.
“Among the ones we’ve sampled, the oldest living trees are around 600 or 700 years old,” Bekker said. “When you combine that with dead (juniper) wood still on the ground, we have over a thousand-year record.”
Still, juniper presents its challenges. Its high sensitivity to moisture and drought means it can sprout an extra ring during a late-season monsoon. During dry years, it might stay dormant and not put on a ring at all.
“So not just counting rings, but assigning a date to each of those rings is very difficult,” Bekker said. “I’m interested to see what happened this year, for example. We had such a wet August and September, I wouldn’t be surprised if we sample trees this fall that have false rings.”
Because of its misleading rings, Dendroclimatologists have held off from sampling juniper in the past, favoring more reliable but shorter-lived trees like pinyon and ponderosa pine. Those samples only date back around 500 years, but they’ve still revealed an unsettling history of horrendous drought.
Based on one of Bekker’s studies released earlier this spring, one of the state’s most severe droughts came in 1492. Three more of the Wasatch’s worse droughts occurred during Christopher Columbus’s lifetime. Dry periods continued to occur through the centuries.
“In the early 1700s, there were 16 consecutive years where moisture levels were below average,” Bekker said. “Imagine that carrying on now.”
Bekker and researchers at the Wasatch Dendroclimatology Research group have reached out to water managers in the state to help them start thinking about those possibilities, including officials at the Weber Basin Conservancy District. While Assistant General Manager Scott Paxman said he’s excited to have past drought data, there’s plenty in the record that concerns him.
“When you’re looking at something in the past like a 15-year extended drought, that’s significant,” Paxman said. “Stuff like that you just hope never happens again, because there’s no planning on how to bridge that kind of drought with a consistent water supply.”
Paxman said the district grappled with some bad droughts in the 1990s and early 2000s, but the last five years brought the worst drought he’s had to manage.
“We didn’t get the snow we typically get, so the supply was low,” he said, “but our demand is so much higher now because of our growing population that we feel it more and it impacts us more.”
While past drought data provides clues to worst case scenarios, Paxman said he still needs more reliable forecasts so he knows what’s coming.
“That’s where we’d really like to see this research go,” he said. “We’d like them to give us something that will help us predict the next five years.”
This year, Bekker became the first researcher to take on the fickle Utah juniper to help build a broader picture of the region’s climate history, which in turn will help with future forecasts.
According to Simon Wang with WADR and the Utah Climate Center, Utah experiences multiple drought cycles on five, 15, 30 and 100-year cycles. The further back the climate data goes, the more fine-tuned their forecasting models become.
“That’s where tree ring data comes in,” Wang said. “They provide good statistics to understand those patterns with higher confidence, so we know if a particular drought is coincidence or random.”
To solve the problem with Utah juniper’s phantom and false rings, Bekker compared samples with different tree species nearby, and with trees at higher elevations that are less sensitive to moisture levels.
“We’ve now gone back into the 800s AD,” he said. “We’re seeing the same kind of thing with drought, but the further back you go, the more the chances increase that you’ll find a real doozy.”
In the 1200s, for example, Bekker found evidence of a 70-year period where the climate remained consistently dry.
“Those are the kinds of things that are way outside the box in terms of what we’re thinking now,” Bekker said. “We’re going to have to think differently, and by ‘we’ I mean everyone.”
Wang has combined Bekker’s tree ring findings with Great Salt Lake levels to help paint a regional picture beyond what’s happening in a single watershed like the Weber, Bear or Provo rivers.
“Each stream has its own character and fluctuates in its own way,” Wang said. “But the lake acts like a giant rain gauge in our region … it collects all those streams into one, and filters out the unwanted noise.”
Current forecasts show the Great Salt Lake will continue to decline for the next few years, but it should start to fill by 2017. There’s a time lag between drought and lake levels, however, meaning moisture levels in snowpack and streams should start to improve a few years before the lake begins to rise.
When asked if that means we’re looking at a decent powder year this winter, Wang was cautiously optimistic.
“We should see a wetter than normal period come back. If it’s not this year, it might be next year,” Wang said. “This is why understanding cycles is important. We can make a prediction for the next five years, but it’s still a challenge to predict what will happen over the next year.”
Climate cycles happen slowly in scale of a human lifetime, and an impending wet period doesn’t mean Utah’s in the clear when it comes to drought. Climate models still show that with human activities leading to a warmer planet, the West is going to continue getting drier overall.
According to Bekker, even without increased greenhouse gases and human influences on the climate, there’s a reason to pay attention.
“I liken it to a bike going along over a bumpy road. If you throw stuff in the spokes, who knows what might happen?” he said. “The record I see in the past means you don’t even need to consider climate change to be a little concerned about water resources in our area.”