Rockies, Alps, Himalayas: More rain, less snow in Northern hemisphere mountains as temperatures rise, says report

The Himalayas and other mountains across the Northern Hemisphere are likely to see 15 per cent more rain for every 1-degree Celsius rise in temperature due to climate change, according to a new study.

Climate change could cause a shift in snowfall to rainfall in mountain regions across the Northern Hemisphere, amplifying rainfall extremes lasting over a few hours to a day, the study published in Nature stated.

This switch from snowfall to rainfall could increase the risk of disasters such as floods, landslides, and soil erosion.

“One quarter of the global population lives in or downstream from mountainous regions,” said Mohammed Ombadi, first author of the paper said in a statement. “They are going to be directly affected by this risk,” he added.

Projected risk of rainfall extremes by the end of this century

Areas in the darkest blue are 8 times more likely to experience an extreme rainfall event (compared to 1950-1979). Credit: Mohammed Ombadi/Berkeley Lab

The findings stress the importance of developing climate adaptation plans to protect the natural and built environments, where 26 per cent of the global population live in or directly downstream of mountainous regions.

Researchers from Lawrence Berkeley National Laboratory, Berkeley and University of Michigan used European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA527) for data between 1950 and 2019. They relied on computer models for future projections.

By combining historical records (1950-2019) datasets with climate model projections (2024-2100), the researchers examined the increase in rainfall extremes in both periods and datasets.

Data from 1950-2019 already shows that this transition from snowfall to rainfall has already been set in motion in the mountain regions of the Northern Hemisphere.

It will continue to increase at a rate of 15 per cent for every 1 degree Celsius rise in temperature. For 2 degrees and 3 degrees rise, the world would see a 30 per cent and 45 per cent increase in rain, respectively.

Not all mountain regions are at high risk. The Himalayas and the North American Pacific Mountain ranges, including the Cascades, Sierra Nevada, and coastal ranges from Canada to Southern California are more threatened than the Rockies or the Alps, the findings showed.

“The Himalayas is one of those hotspot regions where we see an increased risk of rainfall extremes. In fact, our data shows that the Himalayas are likely to see higher rates of increase than other mountainous regions,” Ombadi told Down To Earth.

The researchers speculate the higher risk might be due to changes in atmospheric dynamics

The North American Pacific Mountain range, for example, see a significant portion of snowfall at temperatures just below zero degrees Celsius. A change in air temperature will shift this snowfall to rainfall.

“In other less-threatened mountain ranges, snowfall may occur at very low temperatures below zero degrees,” Ombadi noted.

The research team did not consider mountain regions in Southern Hemisphere due to a paucity of data from the pre-satellite era (before 1979). This, they explained, could lead to biases in estimates of the baseline period (1950–1979). “Such a lack of in situ observations is specifically more common in mountainous region,” they wrote in their study.

Earlier this month, a report from International Centre for Integrated Mountain Development (ICIMOD) found that the Hindu Kush Himalayas have seen a 65 per cent faster loss of glacier mass.

Further, a quarter of snow cover could be lost under a high emissions scenario. The report quoted a study that predicted a decline in snowfall by 30-50 per cent in the Indus Basin, 50-60 per cent in the Ganges, and 50-70 per cent in the Brahmaputra between 2070 and 2100 compared to the average snowfall between 1971 and 2000.

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