Global Warming Intensifies Rainfall Extremes in High-Elevation Regions

A shift from snow to rain in northern hemisphere mountains amplifies extreme rainfall.

An extreme rainfall risk ratio value of 2 means that an event is two times more likely to occur in a future climate. Regions in dark blue color (e.g., Pacific Mountain ranges, Rockies, Himalayas) have high risk of rainfall extremes.

[Reprinted with permission from Ombadi, M., et al. "A Warming-Induced Reduction in Snow Fraction Amplifies Rainfall Extremes." Nature 619, 305–10 (2023). DOI:10.1038/s41586-023-06092-7.]

The Science

Global warming is expected to amplify extreme precipitation events, but the partitioning of rain from snowfall during these events is poorly understood. A new modeling study focuses on changes to rainfall (liquid precipitation) extremes with warming due to its potential impact on flooding, landslides, and erosion. In this study, a multi-institutional team of researchers found a 15% intensity increase per 1°C of warming in mountainous regions, which is twice the previously observed rate for total extreme precipitation. Consequently, high-elevation regions (e.g., Sierra Nevada, Cascades, Rockies, Alps, Himalayas) become vulnerable “hot spots” for future rainfall extremes and are likely to experience amplified risks. This insight enhances understanding of rainfall impacts and associated hazards on specific regions.

The Impact

The results from this research provide information for risk assessment of rainfall-related hazards like floods and landslides in vulnerable regions, which is also home to a significant portion of the global population that resides in mountains and their foothills. Results produce valuable insights for developing effective adaptation and mitigation strategies and enable incorporation of projected increases in rainfall extremes into infrastructure design and natural resources management. Furthermore, the findings identify climate model components requiring improvement to reduce uncertainty in projections of rainfall extremes.

Summary

In a warmer climate, the intensity of extreme precipitation events is expected to increase, posing significant challenges to water sustainability in natural and built environments. Specifically, rainfall extremes are of great concern due to their immediate impact on runoff, as well as their association with floods, landslides, and soil erosion. However, existing scientific studies on precipitation extremes have not distinguished between rainfall and snowfall. This study, by a multi-institutional team of researchers, addresses this gap and reveals that in high-elevation regions of the northern hemisphere, the increase in rainfall extremes is amplified by an average of 15% per degree Celsius of warming—twice the expected rate from atmospheric water vapor increases alone. The team analyzed observations (climate reanalysis data) and undertook model projection studies and demonstrated that this amplified increase is already occurring and is caused by a shift from snow to rain due to warming air temperatures. Moreover, results showed that changes in the fractions of snow and rain explain a significant portion of the intermodel uncertainty in rainfall extremes projections (coefficient of determination 0.47). These findings highlight high-altitude regions as vulnerable hot spots facing future risks from extreme rainfall-related hazards and suggest the need for robust climate adaptation plans to mitigate potential dangers. Furthermore, these results provide a pathway for reducing model uncertainty in rainfall extremes projections.

Principal Investigator

Charuleka Varadharajan
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the U.S. Department of Energy’s (DOE) Office of Science, Biological and Environmental Research (BER) program under Contract No. DE-AC02-05CH11231 for the Calibrated and Systematic Characterization, Attribution, and Detection of Extremes (CASCADE) Science Focus Area and the iNAIADs Early Career Research Project.

Related Links

References

Ombadi, M., et al. "A Warming-Induced Reduction in Snow Fraction Amplifies Rainfall Extremes." Nature 619 305–10  (2023). https://doi.org/10.1038/s41586-023-06092-7.