More research and tools are needed to help predict the effect of climate change on data-sparse mountain cryosphere regions globally, with experts predicting that rising temperatures and shifts in precipitation could have a severe impact on water availability.
With high temperatures, flooding, storms and wildfires becoming more frequent in many places around the world, the effects of climate change on human populations are increasingly apparent. But it is in the Earth’s cryosphere that climate change has been most extreme.
According to NASA, Antarctica and Greenland are losing ice mass at an annual rate of about 150 billion tons and 270 billion tons, respectively. Glaciers, meanwhile, have been consistently shrinking, with the World Glacier Monitoring Service noting that leading up to 2020 there were 33 consecutive years in which glaciers lost, rather than gained, ice.
Many of these glaciers are in mountainous regions, such as the Himalayan glacier of Lirung in Nepal’s Langtang basin, which Philip Kraaijenbrink, an associate professor in Utrecht University’s department of physical geography, has been studying with the assistance of drones since 2013. According to Kraaijenbrink, the glacier has retreated hundreds of feet over the past decade, and there is even vegetation growing on the glacier now. “The situation is really changing,” he comments.
A 2019 Intergovernmental Panel on Climate Change (IPCC) report on high mountain regions noted a general decline in low-elevation snow cover, glaciers and permafrost due to climate change in recent decades. According to the report, snow cover duration has “declined in nearly all regions, especially at lower elevations, on average by five days per decade”.
Water supply issues
The loss of mountain cryosphere is likely to have serious repercussions for large swathes of the global population who rely on the water locked up in mountain snow and ice for their water supply.
Mimi Hughes, a research meteorologist for hydrology at the US National Oceanic and Atmospheric Administration (NOAA), says that “all of the western US states use snowpack to some degree as a water resource”. Meanwhile, the 10 major rivers that originate in the Himalayas supply freshwater to an estimated 1.3 billion people living in their watershed.
“We typically refer to mountains as the water towers of the world,” says Caroline Aubry-Wake, a Canadian post-doctoral researcher currently studying cryosphere/groundwater/surface water interactions in the upper areas of the Langtang basin. “There’s more precipitation in the mountains than in the lowlands, and there are also glaciers and snowpack that act as mini reservoirs for water storage.”
In the case of snowpack, this water is stored over winter and then released as snowmelt in the spring. The agricultural communities that live downstream of these mountain ranges have come to rely on these melt cycles, which are becoming increasingly erratic due to climate change.
In the Indus basin, home to one of the largest irrigation systems in the world, there are several cropping seasons, comments Kraaijenbrink, “but one major cropping season coincides exactly with the glacier and snowmelt period.” He adds, “So if you have less glacier and snowmelt right at the start of your cropping season to irrigate your crops, that’s quite a big deal.”
Ironically, the loss of mountain cryosphere may well increase the amount of downstream water in the short term, says Aubry-Wake, “As glaciers retreat at first, they can provide more water to downstream communities because they’re melting more.”
However, in the long term, water availability will drop sharply as the glacier ice dwindles to nothing. This means that downstream communities, which have grown in the past 30 years as glacier melt provided more water for irrigation, will be faced with a dramatic loss of water availability in the future.
Researchers are also trying to understand the possible impact on the 344 million-plus people who live in mountainous regions globally. According to the findings of an IPCC cross-chapter paper released in 2022, a wide range of human and natural systems in mountains have already been affected by climate change, including terrestrial and aquatic ecosystems, agriculture, tourism and energy production.
Comparing mountain environments to the “canary in the coal mine”, the report’s co-author, Dr Carolina Adler of the Mountain Research Initiative (MRI), noted that, “Mountains offer a specific context in which to observe complex and dynamic global change phenomena, such as climate change, manifesting in rapid and tangible ways.”
Despite the serious impacts of mountain cryosphere loss, this is an area that remains under-researched. One of the reasons is the complex topography of mountains, which even the most high-resolution climate models are too coarse to capture, according to Aubry-Wake.
“There’s a product we’re using that has a 12km resolution,” she says. “But in the mountains, in 12km you can see a 2km vertical difference in altitude. So, a lot of the tools that are used to investigate climate change are not quite good enough to investigate what is going on specifically in the mountains, where temperature and precipitation are changing really fast.”
Added to this is the remoteness of the mountain terrain, which makes conducting field research incredibly challenging. For example, the Langtang basin where Kraaijenbrink and Aubry-Wake have focused their research was chosen in part because it was considered “quite accessible”, notes Kraaijenbrink, even though getting there requires a day-long journey by 4×4 followed by a hike of three to four days.
Moreover, the harshness of the mountain environment often leads to equipment breaking down, with instruments buried under snow, burned in bushfires or destroyed by curious wildlife. With field research in these regions carried out on a yearly basis at best, this can lead to some serious gaps in the data.
Aubry-Wake explains, “It’s really hard to know exactly what’s going on because, on the one hand, the models that we use that work quite well to predict global temperatures and averages don’t work in the mountains. And we also don’t have the data to prove that they don’t work. So simple things like how much snow is in a valley is something that’s really hard to know.”
Measuring snowfall and groundwater
Despite the challenges, researchers are continuing their efforts to build up a picture of how climate change is intersecting with mountain hydrology. Leading the way is Utrecht University’s Department of Physical Geography, which, under the guidance of Professor Walter Immerzeel, has been collecting data in the Langtang basin in Nepal since 2012.
Much of the instrumentation used resembles traditional weather stations, with particular focus on precipitation gauges, which are important for measuring snowfall. Meanwhile, gamma sensors are used to measure a metric called the snow water equivalent (SWE), which is the amount of liquid water in the snow. Imagine taking a parcel of snow and melting it. The height of the water created would be the SWE metric. According to Kraaijenbrink, knowing SWE is important because the relationship between snowpack depth and water content is inexact as “all kinds of things happen to snow that can change the depth of the snowpack but not change the water content”. Knowing the water:snow ratio is also key to understanding how much water is available for future snowmelt.
Another key part of the mountain hydrological cycle is the role played by groundwater. Although this was previously assumed to be trivial, it is now understood that mountain groundwater is a key water source, contributing more than 50% of the water discharge to downstream rivers during periods of low flow.
However, the loss of glaciers and snowpack is threatening the availability of this mountain groundwater, and along with it, its ability to sustain downstream rivers. “Low flows are often occurring when there’s no rain and there’s not a lot of glacier melt – in the Himalayas, during the dry season or in the winter after the monsoon,” says Aubry-Wake.
During these periods, many rivers in the region are “really sustained by all the water that travels through the ground”, she says. “So, if we don’t have as much glacier snowmelt, does that mean that we’re going to have less groundwater and our rivers are going to be drier in the dry season when we don’t have any other water sources?”
Groundwater levels are measured using a variety of techniques, explains Aubry-Wake. To understand how much groundwater is available to begin with, wells are drilled in the field at altitude. (She notes that she chose the Langtang basin partly because the Utrecht team had already installed wells there and had groundwater data going back to 2017.)
To ascertain how much of this groundwater finds its way to rivers, Aubry-Wake uses modeling and hydro-chemical analysis of water samples collected downstream. Her project, which began in October 2022, will run until the end of 2024.
More data needed
Despite the tireless efforts of Aubry-Wake, Kraaijenbrink, Hughes and their peers, it is still too early to say what the future impact of climate change will be on the global mountain cryosphere and the countless millions who rely on it as a water source. Hughes says, “Because there’s so much year-to-year variability in the snowpack, it becomes really challenging to see the long-term shift amidst those big swings.”
But even without this yearly variability, the 10 years of data collected in the Langtang basin by Utrecht University’s team isn’t enough to say anything definitive yet about the impact, notes Kraaijenbrink. That said, none of the researchers are in any doubt that the impact will be far-reaching and serious. “I think climate change is changing everything in all aspects of life at this point,” says Aubry-Wake. The world’s mountain ranges are surely no exception to this trend.
This article originally appeared in the January 2024 issue of Meteorological Technology International. To view the magazine in full, click here.