Thirty-nine years of snowfall extent data mapped in both the northern (a-c) and southern (d-f) hemispheres, with the red edges signifying the number of years snowfall extended to areas for 25%, 50%, and 75% of the year. This suggests an overall contraction of snowfall extent during the 39 year period in both hemispheres.
One of the anticipated impacts of global warming is the change in amount and distribution of snow across the globe. Using multi-satellite and reanalysis data, researchers at the St. Anthony Falls Laboratory (SAFL), University of Minnesota and the National Center for Atmospheric Research are analyzing how global snowfall patterns have changed over the past 40 years.
As global temperatures rise, a lower proportion of winter precipitation falls as snow, which has implications for areas that rely on snow and its meltwater for water supply. However, the changes are unknown at the global scale. To address this, researchers measure wet-bulb temperature, which quantifies air temperature and moisture, to help predict whether precipitation falls as rain or snow over land and ocean. In a newly published study in the Journal of Climate, researchers use multiple reanalysis data from 1979 – 2017 to analyze wet-bulb temperature in the northern and southern hemispheres, including mountainous regions, to better understand how much transition from snowfall to rainfall has occurred over those four decades.
“Approximately 2 billion people across the earth depend on water derived from snow and its meltwater,” says Sagar Tamang, one of the study’s lead authors and PhD student at SAFL and in the Department of Civil, Environmental, and Geo- Engineering (CEGE) at the University of Minnesota. “We need to have a better understanding of how snowfall patterns are changing so we have a benchmark to reference in the future as global temperatures continue to rise.”
Key findings from the study include:
- Wet-bulb temperature has incrementally increased over the past 40 years in the Northern Hemisphere on both land and ocean. This has resulted in a loss in potential snowfall areas – up to 3.5 million square kilometers over land and ocean (roughly equivalent to doubling Alaska’s size).
- Mountain regions of the world are more vulnerable to increasing temperatures. In particular, the Alps, the mountainous regions in the Western US, and the High Mountains of Asia show the steepest declines in potential snowfall areas over the past 40 years.
- The NH latitudes that generally represent the transitional boundary between rain and snowfall occurrence are retreating northward toward the pole.
“While this study focuses more on what's happened in the past, it also provides us insight moving forward,” says Ardeshir Ebtehaj, Tamang's advisor and SAFL faculty and assistant professor in CEGE. “Being able to better understand where and how snowfall patterns have changed across the globe to date can help us prioritize regions where we know water scarcity is going to be an emerging and pressing issue.
The study was funded through the National Aeronautics and Space Administration (NASA) Precipitation Measurement Project (NNX16AO56G), the New (Early Career) Investigator Program award (NIP, 80NSSC18K0742), and the grant from the Terrestrial Hydrology Program (THP, 80NSSC18K152).