Tag Archives: tree ring

California’s snowpack hasn’t been this low since the 1500s

The environmental situation in California is getting worse and worse. According to a new study published in Nature Climate Change, the snow in the Sierra Nevada mountains has reached the lowest levels in the past 500 years, underscoring the severe drought that is already affecting the state.

Drought, heat and climate change

A comparison of an average snowpack year (left) and this year. (Credit: NASA/MODIS)

This weekends, California’s wildfires destroyed over 400 homes and businesses, killing at least one person. California is also experiencing its most severe drought in over 1000 years, and now, the snow has all but melted; these are not all coincidences or separate events – they are all connected to the underlying cause: man-made global warming.

“We should be prepared for this type of snow drought to occur much more frequently because of rising temperatures,” Professor Valerie Trouet of University of Arizona’s tree ring lab said. “Anthropogenic warming is making the drought more severe.”

In areas where the snow was usually five feet thick (1.5 meters), now, there’s barely any snow left.

“This is not just unprecedented over 80 years — it’s unprecedented over 500 years,” she said.

The fact that the snow is melting has much broader implications: the snowpack in the Sierra Nevada mountains is the main source that replenishes the waters in the state, providing over 30% of the entire water supply.

Trees and water

A blue oak tree stands in the Tehachapis Mountains in Kern County, Calif. This tree species is sensitive to winter precipitation and was used to reconstruct the Sierra Nevada snowpack over the last 500 years. (Photo: K.J. Anchukaitis)

Researchers studied tree rings from more than 1,500 trees in California and other trees across the West. Tree rings don’t let us know how old trees are, but they carry within valuable information from the climate of every specific year. Trees develop annual rings of different properties depending on weather, rain, temperature, soil pH, plant nutrition, CO2 concentration etc.

“Trees are remarkable … they are the best recorder of past climate,” she said. Trees like water, she said, so wide rings signify a wet winter while narrow rings show it was a dry winter.

The trees aren’t impacted by the study.

By cross-referencing this information, they were able to find out how much snow fell each winter, and the results are worrying: not only is this the least snow the mountains have seen in 500 years, but things will likely get worse in the future.

“We should be prepared for this type of snow drought to occur much more frequently because of rising temperatures,” Trouet said. She added that man-made global warming is making the drought in California more severe.

Journal Reference: Soumaya Belmecheri, Flurin Babst, Eugene R. Wahl, David W. Stahle & Valerie Trouet – Multi-century evaluation of Sierra Nevada snowpack. Nature Climate Change (2015) doi:10.1038/nclimate2809


Young and in its prime: famous California tree is “only” 777 years old

They call it “Tree 76”, because it stands 76 meters tall (249 feet) above the Muir Woods floor in California. Researchers wanted to see how old Tree 76 is, and they were surprised to see how young it is – at only 777 years old, it’s much younger than the oldest known trees of its kind.

The Sentinel, another giant tree from the same species. Look at the fence at the bottom of the image to truly understand its scale. Image via Wikipedia.

“Tree 76 is one of the larger trees that you can walk near so I think people have been guessing about its age for a long time,” Save the Redwoods League Science Director Emily Burns said. “We know Redwoods can live quite a long time. The oldest one that we know of is 2,500 years old.”

Indeed, trees can get incredibly old. Unrelated to this study, Rachel Sussman is documenting the oldest living things in the world – she found 10,500 year old pines and a 9,550 year old spruce, and there’s also giant sequoias like General Sherman, which can go over 2,000 years old. It was somehow expected that Tree 76 was about the same age, revolving around 1,200 – 1,500 years. But biologists from Humboldt State University showed that age and size don’t necessarily correlate, and the tree was born only in the 13th century – still a very old tree, just not as old as they were expecting. Other, smaller trees from the same species are much older.

“Age and size don’t correlate well,” Burns said, adding that this is the first time the age of 76 age has been determined by scientists.

But even so, Tree 76 was 150 years old when Columbus reached the Americas, and it was alive for half a millennium when the industrial revolution started. It kind of gives you a new sense of scale, doesn’t it?

The tree belongs to a species called Sequoiadendron giganteum, also known as Sierra redwoods; it is the sole living species in the genus Sequoiadendron, and one of three species of coniferous trees known as redwoods. Giant sequoias are the world’s largest single trees and largest living thing by volume (read: The Largest Organism in the World / The Heaviest Organism in the World). Despite being adapted to forest fires and rough conditions, it is very difficult for Sierra redwoods to reproduce, due to the seeds only being able to grow successfully in full sun and in mineral-rich soils, free from competing vegetation.

Biologists nowadays don’t need to cut a tree to know how old it is – they can simply take a core from it. Now, they plan to find clues about medieval climate based on the tree’s rings.

Professor Bekker and a student extract a core sample from a dead tree in Provo canyon

Tree rings reveal worst droughts in the West’s history happened during Christopher Columbus’ lifetime

Professor Bekker and a student extract a core sample from a dead tree in Provo canyon

Professor Bekker and a student extract a core sample from a dead tree in Provo canyon. (C) BYU

Modern climate tracking and water flow records go back only 100 years, but to prepare for the worse, scientists and policy makers alike need to understand how the weather was like in the world many more years prior. A solution is to study the tree rings of certain tree species which bear telltale signs of water levels hundreds of years past, as  Brigham Young University professor Matthew Bekker suggests.

Bekker analyzed rings from drought-sensitive tree species and remarkably found that  the worst drought of this century barely makes the top 10 of a study that extended Utah’s climate record back to the year 1429. Here are some conclusions Bekker could gather simply by closely following tree rings, whose thickness is directly dependent on water intake at the time, using only simple tools like sandpaper and a microscope:

– Long droughts: The year 1703 kicked off 16 years in a row with below average stream flow.

– Intense droughts: The Weber River flowed at just 13 percent of normal in 1580 and dropped below 20 percent in three other periods.

– Consecutive worst-case scenarios: The most severe drought in the record began in 1492, and four of the five worst droughts all happened during Christopher Columbus’ lifetime.

“We’re conservatively estimating the severity of these droughts that hit before the modern record, and we still see some that are kind of scary if they were to happen again,” said Bekker, a geography professor at BYU. “We would really have to change the way we do things here.”



This analysis which goes back more than 500 years tells us that the West was once subjected to drought fluctuations much more severe than anything we’ve seen in recent history. If this happened before, then it can certainly happen in the future. The real questions that remain to be answered is when these periods of severe drought might come again in the future, and what signs can scientists look for to forecast their coming.

“We’re trying to work with water managers to show the different flavors of droughts this region has had,” said Bekker. “These are scenarios you need to build into your models to know how to plan for the future.”

The findings were reported in the Journal of the American Water Resources Association.