Every Degree of Warming Increases Extreme Rainfall in Northern Hemisphere Mountain Regions

Nature, 28 June 2023

Rising temperatures turn snowfall into rainfall, increasing the susceptibility of mountain regions to extreme rain and hazards such as floods, landslides, and soil erosion. This study provides the first assessment of high-altitude “hotspots” across the Northern Hemisphere, which face compounding hazards as atmospheric warming increases the fraction of water that precipitates as rain rather than snow. Researchers found that extreme rainfall in mountain regions steadily increases with each degree of warming. For every +1°C above the global average today, higher elevations will experience on average 15% more extreme rainfall, nearly double the rate previously predicted. The linear trend continues as temperatures rise; for example, 3°C of additional warming would result in 45% more rainfall in mountain areas as snow coverts to rain; with risks actually greatest at higher elevations.

The regions at greatest risk of extreme rainfall include the North American Pacific mountain ranges (the Cascades, Sierra Nevada, and coastal ranges from Canada to Southern California), the Himalayas, and high latitudes in the Arctic. The number of deadly floods and landslides around the world have increased in recent decades, with most occurring in places exposed to extreme rainfall. These hazards come on top of those posed by melting glaciers in the same mountain ranges and valleys. The study serves as a map, highlighting regions that are most vulnerable to extreme rainfall, and underscores that every fraction of a degree matters not just for those living in the high mountains but also for the billions of people living downstream, reliant on mountain water stability for agriculture, infrastructure, electricity and safety. These findings make it clear: rain-related hazards in mountain regions and downstream will continue to grow unless emissions are limited to remain within the 1.5°C guardrail of the Paris Agreement.

https://www.nature.com/articles/s41586-023-06092-7