Scientists Warn: Warming Induces Increased Extreme Rain, Rather than Snow, Over Mountains, Posing a Concern

A new study has found that a warming world is causing major snowfalls over mountains to transform into extreme rain, exacerbating both dangerous flooding and long-term water shortages. The study, based on measurements of rain and snow since 1950 and computer simulations, reveals that for every degree Fahrenheit of warming, extreme rainfall at higher elevation increases by 8.3% (15% for every degree Celsius). This trend has significant implications for regions prone to heavy rain in mountains, including increased flooding, landslides, and erosion.

Unlike snow, which can be gradually released as it melts and replenish reservoirs, heavy rain in mountains poses immediate challenges. Lead author Mohammed Ombadi, a hydrologist and climate scientist at Lawrence Berkeley National Laboratory, emphasizes that the study’s findings suggest this issue is not a future projection but something that has already been happening for several decades.

As the world approaches the internationally agreed threshold of 1.5 degrees Celsius to prevent the worst impacts of climate change, Ombadi points out that each degree of warming comes with an additional 15% increase in extreme rain over mountains. This increase in mountainous rainfall is more than twice the global average increase caused by warming air holding more water.

The study, which focused on the Northern Hemisphere, found that rainfall intensity at higher altitudes increased the most at around 10,000 feet. This includes regions such as the American West, the Appalachian Mountains, the Himalayas, Tian Shan, Hindu Kush, and the Alps. Approximately a quarter of the global population resides in areas susceptible to extreme rain and flooding from mountains.

The consequences of the shift from snow to rain are significant. The 2022 floods in Pakistan, which claimed over 1,700 lives and submerged a third of the country, provide a tragic example. In addition to the immediate dangers posed by flooding, heavy rain can also harm food production and impact long-term water supply. Reduced snowfall will diminish water supply in the future, leading to more short-term runoff, less snowpack for groundwater recharge, and decreased stream flows. This poses a serious challenge for water management in mountainous regions, which are major suppliers of water for the West.

In regions already grappling with prolonged droughts, heavy rainfall exacerbates the difficulty of water management. Water managers face the dilemma of either reducing water use due to low reservoir levels in anticipation of sudden mountain runoff or constructing expensive new reservoirs. The implications of these choices are far-reaching and affect the sustainability of water supply in the face of climate change.

Overall, the study underscores the urgent need for effective adaptation strategies to address the increasing challenges posed by extreme rainfall in mountainous regions. By recognizing and addressing the transforming dynamics of precipitation patterns, societies can strive towards resilient water management and minimize the devastating impacts of flooding and water shortages.

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