Some mountain communities find themselves parched when water needs don’t sync with glacial melt. In Ladakh, India, a region nestled between the Himalayan and Karakoram ranges, people have been storing water in towering cones of ice called ice stupas each winter since 2014. These structures tide communities over when meltwater isn’t sufficient to water crops. A new study published in Frontiers in Earth Science digs into how these structures form and where else they may work on the basis of climate.
Adaptation techniques are needed for dry, high-altitude areas that face water stress, said Adina Racoviteanu, a glaciologist and remote sensing researcher at University Grenoble Alpes who wasn’t part of the study. Ice stupas have a lot of potential, but their water storage hadn’t been quantified, she said.
Banking Water in Ice
Farmers in Ladakh typically divert meltwater from glacial streams to irrigate, said Suryanarayanan Balasubramanian, a glaciologist at the University of Fribourg in Switzerland and the Himalayan Institute of Alternatives, Ladakh, in Leh, India. That flow of meltwater peaks in summer, but water demand for farming is highest in the spring. Ice stupas can capture water from a stream, spring, or lake during winter months. Far smaller and at a lower altitude than a glacier, the stupas melt slowly during spring.
Ice stupas get their name from their conical shape, which resembles the spires atop some Buddhist temples. And their construction requires minimal equipment—just a pipeline to supply water and a fountain. Flowing a few kilometers downhill to the ice stupa site, gravity-fed water moves up a vertical pipe, sprays out through a nozzle, and eventually freezes into a bumpy cone. As the structure grows, the pipe in the stupa’s center is extended. In Ladakh, one ice stupa grew to 30 meters tall and stored 8 million liters of water, Balasubramanian said.
But farmers need to know how much water such structures will provide daily, and their storage can vary drastically on the basis of local weather, Balasubramanian said. So Balasubramanian and his team set out to create a model to estimate how much water ice stupas provide.
The team built three ice stupas: two in Guttannen, Switzerland, and one in Ladakh. At these locations, they tracked weather conditions, such as temperature, humidity, and precipitation, and monitored the fountains’ flow. They incorporated these factors into a model that uses equations that capture the physics of water freezing and ice melting or vaporizing. The team also documented the size of the stupas through monthly drone surveys, using the data to tune and test their model.
Adaptation and Desperation
Ladakh sits at higher elevation and is more arid and less cloudy than the Swiss site. “We see that these climatic differences result also in a big difference of the ice volume,” said Nico Mölg, a remote sensing scientist at the research company ENVEO (ENVironmental Earth Observation IT GmbH) who wasn’t part of the work. Ladakh’s maximum ice stupa volume was 4 times that of the Swiss site.
Cold, dry climates mean that water is more likely to sublimate, forming water vapor from solid ice. While sublimation removes ice from the stupa, it also decreases its surface temperature. That improves the freezing of water from the fountain. Cloudier skies, on the other hand, contribute to melting the stupa, the team found. Without clouds, sunlight falls on only the Sun-facing surface of the cone. But clouds diffuse sunlight, so that solar radiation falls on the entire stupa surface, leading to greater melting. The model results were within 18% of each ice stupa’s maximum volume over the course of the study, the team reports.
Currently, around 80% of the water sprayed on the stupa is lost, the team found. The vast majority of water sprayed runs off before freezing. To limit these losses, larger or multiple structures could be built at any given site. The model could be used to tailor the fountain’s flow for a particular site, Balasubramanian said. The team is also studying automating the valves and using solar panels to power them. That may be too expensive for smallholder farms, but it may be feasible for larger installations, he said.
It’s not clear how well the model applies to places where the climatic conditions differ greatly from those in the study, Racoviteanu said. The researchers may need to collect data in such locations to further tune and test their model.
But in areas where the weather resembles that of Ladakh, such as locales in central Asia and the Andes, ice stupas may help communities adapt to water stress, which is worsening with climate change. Farmers in Chile, Nepal, and other regions of northern India are creating ice stupas. “It’s already happening,” Balasubramanian said.
Building ice stupas isn’t going to bring glaciers back or stop them from melting, Balasubramanian was quick to note. “At the end of the day, it’s an act of desperation. This is not a technology that can solve anything. It’s just going to buy a little bit more time for these communities.”
—Carolyn Wilke (@CarolynMWilke), Science Writer