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Yangel Bin Laden
The National Centre for Hydrology and Meteorology (NCHM) is conducting a study to assess the contribution of different water sources to the Mochu River. The study aims to enhance the understanding of the hydrological processes that control the flow of rivers in these basins.
This study is the third of its kind, with similar studies previously conducted on Chamkharchhu and Pachhu.
For this study, we collected water samples from all sources of the river (e.g., groundwater, tributaries, snow, glaciers) in all seasons.
The Mochu River is the western branch of the Punasangchu River and consists of two tributaries, one originating in the Masangaon region in the east and the other in the Gunchintag region in the west. The sub-basin consists of 66 glacial lakes covering an area of 4.25 square kilometers.
Mochu is also one of the three major sub-basins of Punasangchu.
Understanding these processes is crucial for assessing the vulnerability of water supplies to downstream populations, especially in the context of climate change, said Kama, head of the cryosphere services department.
The International Centre for Integrated Mountain Development (ICIMOD) recently released its 2024 Snow Update Report, which shows that snow cover in the Hindu Kush Himalayas (HKH) has dropped by 20% between November 2023 and April 2024. This is the lowest recorded in the past two decades, affecting water security for millions of people in the HKH region and billions downstream. Bhutan is located in the HKH region.
Glacial meltwater and snow play a key role in the flow of Bhutan’s rivers and are essential for hydroelectric power generation.
Asia’s glaciers are often called “water towers” because they store large amounts of ice and gradually release meltwater to feed major river systems.
In Bhutan, previous studies have also shown that glaciers are an important source of water for rivers.
A study of Chamkharchhu conducted by lecturers at Sherubthai College between 2014 and 2017 found that glacial meltwater contributes 23% to Chamkharchhu’s water supply before the monsoon, while snowmelt contributes 39%.
“The Pacho survey reported similar results, showing that glaciers and snow are the main sources of water for the rivers, which is significant,” Kama said. “Imagine what the rivers would be like under the same climate conditions when glaciers are the main contributors to water for these rivers.”
In Pahu, glacial meltwater and groundwater were the major contributors to river flow in all sampling seasons, contributing an average of 49.6%.
Kama said snowfall patterns also change with erratic frequency, although there is no data to support this claim. “From my personal experience, Lunana has not had snow in July since 2009.”
Executive glaciologist Phuntsho Tshering said our glaciers are in bad shape. “Most glaciers have exceeded the equilibrium line altitude (ELA), which divides the glacier into two parts. One side needs continuous snow accumulation to replenish the other side. If there is not enough snowfall, the ELA will exceed the equilibrium line altitude, causing the glacier to melt.”
He said understanding the various factors that influence water sources and river flows is important to identify and understand the contribution of each source of the river, which is why studies like this are crucial. “We have completed the sampling and are yet to send the last sample to India for evaluation. The results may take a whole financial year to come out.”
The research is expected to inform governments on water resource management, climate adaptation strategies and policy development to ensure sustainable water supply and mitigate the impacts of climate change, among other things.
Globally, such research provides critical data support for government work.
In the United States, for example, management of the Colorado River exemplifies how governments use river water research: they allocate water rights, manage dams based on flow patterns, protect ecosystems, and develop drought mitigation plans that ensure equitable distribution and environmental sustainability across multiple states and sectors.
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