The “Asian water tower” is losing 24 billion tonnes of groundwater every year

High Mountain Asia, frequently dubbed the "Asian water tower," faces a growing crisis as groundwater reserves diminish at a concerning rate, according to a recent satellite-based study. This vast region is a vital source of water, supporting farming, urban areas, and ecosystems across more than a dozen downstream countries, serving hundreds of millions of people.

At the heart of this issue lies the alarming reality that the region's groundwater storage is dwindling by approximately 24.2 billion tonnes annually. Led by Professor Shudong Wang of the Chinese Academy of Sciences, the research team overcame significant challenges in understanding the groundwater situation in this complex mountainous landscape, primarily due to limited on-the-ground data.

Their findings, published in Environmental Research Letters, utilized an AI-powered model that incorporated satellite observations, Earth system modeling, and explainable AI to reconstruct two decades of groundwater storage changes. This approach revealed that about two-thirds of the High Mountain Asia experienced a decline in groundwater storage between 2003 and 2020.

The areas with the most significant loss were those with high population densities and high irrigation demands, such as the Ganges-Brahmaputra, Indus, and Amu Darya basins. However, some higher elevation inland areas saw localized increases in groundwater storage. The leading cause of this decline is climate-related factors, accounting for nearly half of the observed variation in groundwater storage, with the cryosphere playing a particularly critical role.

Human water withdrawals have also significantly contributed to the depletion, especially in downstream agricultural regions relying heavily on irrigation, a trend that intensified after 2010. The study projects that groundwater losses will persist if current water usage patterns continue. In some locations, increased glacier melt might temporarily mitigate the pace of groundwater decline around the 2060s, but this temporary buffer effect cannot last forever and is expected to be succeeded by accelerated losses.

If current water use patterns remain unchanged, groundwater depletion could escalate further, posing a growing threat to the agricultural regions that depend on these reserves downstream. The researchers employed an innovative framework that combined existing scientific knowledge with large amounts of observational data. By leveraging multiple satellite sensors, they estimated the groundwater storage changes over the past 20 years.

This framework incorporated a lightweight Transformer architecture designed to account for hydrological memory and delayed effects within mountainous catchments. Additionally, they used explainable machine learning methods to identify the physical factors associated with the identified groundwater changes. To validate their results, the team compared their findings with thousands of measurements from groundwater wells and independent datasets, providing additional support for their conclusions.

This approach overcame long-standing difficulties in studying the High Mountain Asia, such as rugged terrain and incomplete information about human water use. Funded by the National Key R&D Program of China and the Key Program of the National Natural Science Foundation of China, this research paves the way for a better understanding of groundwater dynamics in this crucial water tower.