A new study has found that a warming world is turning some of the larger snowfall in the mountains into extreme rain, worsening both the dangerous floods that hit Pakistan last year as well as long-term water shortages.
Using rain and snow measurements from the 1950s and computer simulations for future climate, scientists calculated that for every degree Fahrenheit the world warmed, extreme precipitation at high elevations would increase by 8.3%, according to a study in Wednesday’s Journal. (15% for every degree Celsius) increases. Nature.
Scientists said heavy rain in the mountains causes far more problems than heavy snowfall, including floods, landslides and erosion. And rain is not easily stored like snowpack which can recharge reservoirs in the spring and summer.
“This is not just a distant problem that is predicted to happen in the future, but the data is actually telling us that it is already happening and we can see it in the last few decades of data,” said lead author Mohamed Ombadi. lets see.” Hydrologist and climate scientist at Lawrence Berkeley National Laboratory.
As the world warms to the internationally agreed 1.5 °C (2.7 °F) limit to prevent the worst effects of climate change, this study suggests that “every degree (C) counts because it comes with an additional 15% increase” said Ombadi, of the extreme rain in the mountains. The per-degree increase in precipitation in the mountains is more than double the increase from warmer air holding more water in the rest of the world.
The study looked at only the heaviest rainfall each year over six decades in the Northern Hemisphere, showing that as altitude increased, so did the turbocharging of rainfall. The greatest increase in rainfall was observed at about 10,000 feet (3,000 m). This includes much of the American West, where Ombadi said “it’s very clear”, as well as parts of the Appalachian Mountains. Another big hotspot in Asia is the Himalayas, the Tian Shan and the Hindu Kush mountains, with the Alps also affected.
About one in four people on Earth live in an area so close to mountains or slopes that they would be affected by extreme rain and flooding, Ombadi said.
Ombadi said, this means that the flood coming from the mountains will be similar to the flood that killed more than 1,700 people in Pakistan and submerged a third of the country. But he added that he has not done an exact study of Pakistan’s 2022 floods, so there could be some small differences.
UCLA climate hydrologist Park Williams, who was not part of the research, said the study makes sense and “the implications are serious”. Scientists expect more precipitation with warmer temperatures, but the flood effect of heavy snow is reduced because it takes time to melt and it’s easier to monitor the snowpack to see what’s happening, he said.
“But as the proportion of mountain precipitation decreases with snow fall, flood hazards could increase especially rapidly,” Williams said.
In the American West it severely affects climates in two different ways, said study co-author Charuleka Varadarajan, a laboratory climate scientist and hydrologist.
“Extreme rain like this is going to make the floods worse. And then you have to find out where that water is going?” He said. “We have such a serious issue right now with Tulare Lake flooding and related issues in the Sierras.”
Ombadi said the floods could also damage food production. He pointed to an estimate by the California Department of Agriculture that this year’s torrential rains caused $89 million in crop and livestock damage.
But in the long term, another problem is the water supply. When there is heavy snowfall in the west in winter, that snow melts slowly in the spring and summer, filling reservoirs where it may be needed later.
“In the future it will reduce your snow, your water supply,” Varadarajan said. “You’re going to have more short-term runoff that will lead to more flooding and less snowfall that recharges the groundwater and that groundwater ultimately helps maintain stream flow.”
“These mountain systems supply most of the water in the west, so any reduction in water supply will be significant in terms of water management,” he said.
In times of drought, Williams said — and much of the West is battling a megadrought lasting more than 20 years — water managers prefer to keep water levels in reservoirs high, which they can do with heavy snowpack because it Melts slowly. But in heavy rains they cannot do so.
As warming increases rainfall extremes, societies may need to adjust water use due to low water levels in reservoirs to absorb potentially large-scale sudden mountain runoff or build costly new reservoirs, Williams said. Have to choose between making cuts.
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