A remarkable decrease in snowfall in the Himalayas and Hindu Kush regions has set off alarm bells for water security in regions fed by glacial waters, including the Indus River Basin.
This was disclosed in a report prepared by the latest Hindu Kush and Himalayas Snow Update 2024 by the International Centre for Integrated Mountain Development (ICIMOD) this week.
“We’ve seen a pattern of decreasing amounts and persistence of snow across the Hindu Kush Himalaya, with 13 of the past 22 years registering lower than normal seasonal snow persistence,” said ICIMOD Cryosphere Specialist Sher Muhammad, author of the Snow Update Report 2024.
The update noted that snow persistence, the fraction of time snow remains on the ground, has significantly reduced in the Hindu Kush and Himalaya (HKH) region this year. This has serious water security implications for some 1.65 billion people who live downstream from the largest glacial body outside the polar regions.
The update said snowmelt provides approximately 23% of the total water flow for 12 major river basins that originate high in the HKH region. This includes the Indus River Basin, the Ganges River Basin, the Yangtze River basin, the Mekong River basin, the Yellow River basin, the Tibetan Plateau, the Amu Darya River basin, the Helmand River basin among others.
While its contribution to the water supply varies from river to river, it represents 74% of river flow to the Amu Darya, 77% of Helmand’s flow, and 40% of the Indus’ flow.
“This is a wake-up call for researchers, policymakers, and downstream communities: lower accumulation of snow and fluctuating snow levels pose a very serious increased risk of water shortages, particularly this year.”
Monitoring reports show that this year, snow levels are almost a fifth below normal across the region, with figures falling dramatically in the west, where snow contributes the most to water supply.
The Helmand river basin showed the most dramatic fall in snow persistence, at 31.8% below normal. This was lower than its lowest level recorded in 2018, when it saw a 42% reduction.
Snow persistence fell to 23.3% below normal in the Indus Basin, marking the lowest level in the past 22 years. The previous lowest year for this Basin was 2018, with a 9.4% shortfall.
The region with the lowest variation from normal snow persistence this year was the Mekong basin, where snow persistence was around 1% below normal.
ICIMOD’s Senior Cryosphere Specialist Miriam Jackson emphasised the need to take proactive measures. “We encourage relevant agencies to take proactive measures to address possible drought situations, especially in the early summer, update plans to accommodate water stress, and notify communities of the risks.
“Beyond that, it’s clear that governments and people in this region need urgent support to help them adapt to changes in snow patterns that carbon emissions have already locked in.
“And that G20 countries need to cut emissions faster than ever before to prevent even more changes that will prove disastrous to major population centres and industries that rely on snowmelt in the mountains.”
Major rivers affected
In the Indus River basin, seasonal snow persistence declined noticeably in 2018, with a deviation of 9.4% from the average. In contrast, the highest snow persistence above normal was recorded in 2020, with a value of 15.5%. However, this year, snow persistence had remarkably declined, falling 23.3% below normal levels, with some positive patterns on the southern sides, mostly in the lower altitudes.
The years are from left to right for each sub-basin. The values on the bar are % changes in the year.
In the Amu Darya River basin, the percentage change in seasonal snow persistence previously reached its lowest point in the last 22 years in 2018, with a 17.7% reduction. Conversely, in 2008, the changes in snow persistence reached its highest level, peaking at 32.1%, suggesting a significant increase in snowfall during that period. The current year exhibits the lowest snow persistence, with 28.2% below normal. This assessment highlights the dynamic nature of seasonal snow in the region and emphasises the need for continued dissemination of snow information to better understand and manage the impacts of these long-term changes.
In the Brahmaputra River basin, 2021 experienced the lowest seasonal snow persistence, dropping well below average at 15.5%. The highest recorded snow persistence occurred in 2019, reaching 27.1%. This year, the current snow persistence is also notably below normal at 14.6%.
Significant fluctuations have occurred in the Ganges River Basin over the past 22 years. Prior to 2024, the year 2018 had the lowest snow persistence, at 15.2%, while the highest, 25.6%, was recorded in 2015. The current year has shown the lowest snow persistence, with a value of 17%, which sharply contrasts between the southern and northern sides.
The Helmand River basin experienced remarkably low snow persistence during the 2018 season, significantly below the average by a margin of 41.9%. However, in stark contrast, 2020 showcased the highest snow persistence in the past 22 years, surpassing the average by a notable 44%. This year stands as the second lowest in terms of snow persistence, with a decrease of 31.8% below normal levels and some spatial variations on the western side.
The years are from left to right for each sub-basin. The values on the bar are % changes in the year.
In the Irrawaddy River basin, seasonal snow persistence has fluctuated yearly for the past 22 years. The changes remain below 15% except for 2023, with above-normal snow of 19.1%. In 2017, snow persistence fell below the average by 12.5%, the lowest in the past 22 years. This year’s snow persistence is slightly below normal, with a value of 2.4% having significant spatial heterogeneity.
In the Mekong River basin, seasonal snow persistence variability has increased in the last few years. The most negative snow persistence was observed in 2021, falling below the average by 38.4%. The years 2019 and 2020 witnessed a significant increase in snow persistence, surpassing the normal levels by 68.8% and 52.5%, respectively. This year, snow persistence is slightly below normal at 1.1%.
The Salween River basin has also experienced an increased heterogeneity in snow persistence over the past few years. Like the Mekong River Basin, the most notable decrease in snow persistence was observed in 2021, with a deviation of 28% from the normal levels. The years 2019 and 2020 have witnessed a significant increase in snow persistence, surpassing the normal levels by 30.6% and 35%, respectively. Conversely, the current year has seen a slightly below-normal snow persistence, with an average of 2.4%.
The Tarim River Basin witnessed a significant decrease in long-term snow persistence in the past 22 years. The trends in snow persistence over the past 22 years, with 2003 and 2006 displaying the most positive values, 26.6% and 28.5% respectively. Notably, this year, there is a significant decrease in snow persistence with a value of 27.8%, lowest in the past 22 years.
In the Tibetan Plateau, 2018 experienced the lowest seasonal snow persistency, reaching a value of 34.7%. Conversely, the highest snow persistence was observed in 2020, reaching 63.3%. This year, snow persistence is below normal with a value of 14.8% and exhibits considerable spatial variability throughout the Basin.
In the Yangtze River basin, 2017 experienced the lowest seasonal snow persistency, reaching a value of 27.9%. In contrast, the highest snow persistence was observed in 2008, with a remarkable increase of 50.6% above normal. The long-term trend in snow persistence is significantly negative, with this year also showing 13.2% below normal.
In the Yellow River basin, the seasonal snow persistence reached its lowest point in 2015, remaining significantly below average with a deviation of 42.2%. Conversely, the highest snow persistence was observed in 2008, surpassing the normal levels by an impressive 74.5%. In 2024, the snow persistence remains above normal, exceeding the normal value by 20.2%.