Climate challenges

The Puna Tsang Chu River flows from the snow-capped peaks in the Himalayas through central-west Bhutan, powering several hydroelectric plants, which is the main source of energy in Bhutan.

And it’s not just clean energy that contributes to the country's green credentials. One of the pillars of the country's development concept of "Gross National Happiness" is environment conservation. It's probably the first country in the world where the constitution states that a minimum of 60 percent of the land be maintained under forest cover at all times.

Despite the green policies, Bhutan’s environment has been suffering in recent years. The glaciers feeding the rivers are shrinking and the melt water is forcing up water levels in the Punakha valley's glacial lakes. The lakes could burst their banks and submerge the surrounding towns and villages, raising fears among residents.

"I feel concerned when it's a bright sunny week because we've been told that the sun makes the glaciers melt," Mahum, who runs a grocery shop near the banks of the river, told DW. "I am scared when I hear the river at night and always leave the lights on."

Mahum and her neighbors didn't know they had anything to worry about until a few years ago, when officials told them their village of Samdinkha was in a high-risk zone though the valley lies 3,000 meters below the glacial lakes. A major flood in the area in 1994, caused by a bursting of one of the glacier lakes, killed 22 people.

Early warning system

Now, people living near the river are trained to evacuate when newly installed flood alarms go off. "It's a very distinct sound," Tauchu, the elected traditional leader of the district, said. "When you hear it, you'll know that it's not a honking car or a mobile phone and you'll know that you have to evacuate now."

Once the alarm goes off, indicating that one of the glacier lakes has burst its banks, village residents have at least three hours until the water reaches the village, according to Tauchu. A large school building has been assigned as an evacuation place in case of emergency.

The flood watch towers are monitored from a control room in the town of Wangdi, which is an hour's drive away from the Samdinkha village. Ganesh Pradhan and Zangmo live in Wangdi and use a computer to constantly monitor the water levels of four glacier lakes in the region. They receive an hourly update from two men measuring the water levels up in the mountains.

"When the current water level, which is at 6.99 increases to 7.8, then it will give an alert sound," Zangmo said. The early warning system was built after the 1994 floods. There are now 14 flood watch towers that include sirens. They are located along the river, near villages, hydro-electric plants and other key areas.

Changing rainfall poses problems

While the threat of floods remains, Bhutan has been grappling with another major environmental challenge – erractic rainfall. Fluctuating rain patterns has made it difficult for the country’s hydro-power plants to generate consistent levels of electricity. That’s because most of the plants are run-of-the-river projects – a type of technology where little or no water storage is provided.

"Over the last few years, we've not been able to get a continuous, good trend of rainfall," engineer Karma Tenzin, who works at the Basochu hydropower plant, said. "In fact last year, we had the lowest generation since commissioning. The rain patterns have been really erratic."

The change in rainfall, as well as the decline of glaciers, has been confirmed by data research done over the past 10 to 12 years, according to Chhimi Dorji of the government's Snow and Glacier Division.

"Glacier coverage in Bhutan is decreasing, the maximum temperature is increasing, and there is a decrease in precipitation," she said. "But the volume of water in the rivers is increasing over the years. It's probably because of those glacier melts, that the discharge is increasing even when the actual rainfall is decreasing.“

Hydro power vital for economy

Hydro power is the backbone of Bhutan's economy and the electricity generated along the Puna Tsang Chu River supplies 90 percent of Bhutanese households.

Bhutan also exports this valuable energy to countries like India, bringing in much-needed revenue. India is now a major investor in Bhutan’s energy sector and is currently financing expansion and construction of hydro power projects set to increase Bhutan's total capacity from almost 1,500 million joules per second to 10,000 joules per second by 2020.

But Peljor Dorji, an environmentalist and advisor to the government's National Environment Commission, is not so sure this hydro power boom is a positive development.

"A lot of people say that when you do run-of-the-river schemes, it's green. I don't buy that. It is still something which obstructs the course of the river," he said.

Dorji pointed out that the decision to set up and expand hydro projects was made too hastily. "They should've done more studies," Dorji said, "It's not like Bhutan is going to use all the power it's generating – it's all meant for export."

Dorji is worried Bhutan’s ambitions to modernize and boost revenue from exports could pose the next big threat to the country’s already fragile environment.