The study is one of several taking place to determine glacial recession and future impacts

Climate: Using trees in Bhutan, some as old as 650 years, a study has found that temperatures are indeed rising in this region.

The study, conducted by six researchers, including a Bhutanese, found that the first decade of this century has been the warmest in the past 638 years (1376 to 2013), which coincides with the timing of glaciers receding that continues today.

While the research found that a similar warm period had occurred in 1390, it was only for about a decade.

The findings of the study are significant as continuous instrumental records of climate in Bhutan, longer than 35 years, do not exist.

The researchers studied the growth rings of trees to measure summer temperatures (June-August).

This is the first time such a study was conducted in Bhutan, it is pointed out in the study. Bhutan is a suitable place for “paleoclimate reconstruction” because 72.5 percent of its land is still covered by forests, it adds. “There are few places left in the Himalaya that still retain as much old-growth forest as Bhutan.”

One of the report’s authors, PJ Krusic, who works for the department of physical geography and quaternary geology, Stockholm university, said that so far the oldest tress found in Bhutan were nearly 800 years old and located east of Yotong la.

“Here for some reason, the forests have been left undisturbed by both natural and human impacts,” he said.

“Another location, where the samples for the article were collected, is southeast of Ura. There we have found trees as old as 650 years,” he added.

However, he said old trees are still difficult to find in Bhutan because wood is a popular building and energy resource, and geophysical processes like erosion, landslides, rockfalls, floods, and heavy snows, among others, are still active in the Himalayan region. “In short, for an organism without the capacity to move, living in the Himalaya is a risky venture,” he said.

PJ Krusic explained how the growth rings of the trees were used. He said that it was similar to a garden’s harvest being determined by the amount of care and other input like sunlight and water, it received. “This is the same for trees, trees need water, sunlight, nutrients and comfortable temperatures to grow. Measuring the size of each ring is the equivalent of measuring the amount of harvest from your garden,” he said. “In Bhutan, and much of the high Himalaya, plant growth is controlled most by temperature, when the temperatures during the growing season stay really low the spruce trees we studied do not grow so well and that is reflected by a small, narrow, ring.”

The findings of the study have implications on other studies underway such as glacier recession.

PJ Krusic said the research team is involved in one such study in Bhutan in collaboration with the departments of forest, and hydrology and meteorology, and scientists in the US.

“For this we need long records of temperature from Bhutan which do not exist except in natural archives like the trees in our study,” he said. “Preliminary results show that when temperatures rise, glaciers melt fast. Exactly how fast for every degree of annual temperature increase is exactly what we are going to find out.”

The study is also attempting to find out how water flow and Bhutan’s hydropower dams may be affected in coming decades.

PJ Krusic explained that before such an answer could be provided, a mathematical equation has to be developed to show how much melting would occur for every degree of warmth. For this, a history of temperature changes and glacier melting is required to calibrate and verify the equations, for which a number of collaborative studies are being carried out to measure stream flow and changes to glaciers.

“The problem is we really have little background information to work with so we have to be creative and find natural records preserved in trees, lakes, and glacier moraines that do have the information we are missing,” PJ Krusic said.

In reference to hydropower dams, PJ Krusic said that careful planning is required for such large scale geo-engineering projects. “Any miscalculation on future stream flow could have costly impacts,” he said. “What we know from history is one needs long records of temperature and stream flow to accurately scale such projects.”

He provided an example of the Colorado river in western USA. “During the early 20th century this region of North America was experiencing an exceptionally wet period, a pluvial. It was at this time engineers were building dams along the Colorado and selling water rights,” he said. “Well today this region is the driest in the US and the lakes behind the dams are at their lowest levels ever,” he added. “In my opinion any proposal for a new hydro project today better be accompanied by a thorough fact finding process that includes climate change impacts.”

The study, 638 years of summer temperature variability over the Bhutanese Himalaya, is available online.

Gyalsten K Dorji