As the resident “local hydrologist” living on Rosebud Creek in Absarokee, Montana in June 2022, I watched wide-eyed as the dark floodwaters sent large trees, sheds and even a hot tub sailing past our house. I was called on to address the likelihood of recurrence of such disaster. Conventional statistics held that this flood had a probability of less than 0.2% (1 in 500 years). But this assumes an unchanging climate, which both science and experience rebut. How do you explain this to the public?
Let’s make an analogy to monetary inflation. We know that as inflation creeps upward the cost of most labor and materials increases. Similarly, greenhouse gas emissions cause an increasing imbalance of atmospheric energy that drives up average temperatures of the atmosphere, land, and oceans. Higher global temperatures affect every part of the hydrologic cycle–more potential evaporation and transpiration, drier soils, increasing intensity of both storms and droughts, less snow and ice cover, and flashier streams.
Just like inflation, we track climate trends with key numbers, which can be drawn from federal and state databases and scientific publications, including the Montana Climate Assessment (http://montanaclimate.org). A principal indicator of atmospheric energy is mean global temperature. From 1951 to 2020, global average temperature has increased nearly 2°F, with the last seven years (2014-2020) being the warmest on record according to the National Aeronautics and Space Administration (NASA). Average temperatures increased in Montana by 2-3°F during this period, with average winter-spring temperatures increasing most, 3.9°F.
Climate numbers, like inflation, affect all Montanans, with some of us impacted more than others–irrigated and dryland farmers, ranchers, water suppliers, hunters and fishers, and recreationalists. Producers in Montana might appreciate that the length of the growing season increased by 9.5 days in the past three decades, but the downside has been decreasing soil moisture due to greater evapotranspiration and drier summers.
Snowpack in the mountains is money in the bank for Montana agriculture, cities, and our way of life. Winters of abundance and winters of deficit are normal, but as winters have warmed, snowpack west of the continental divide has declined on average by 20% from 1940-2015. Summer water shortages are compounded due to earlier melt. The average date of peak flow in Montana streams is 1-3 weeks earlier than in the 1940s. This trend, coupled with higher summer temperatures and longer growing seasons, causes longer and more severe streamflow deficits in late summer.
For the Blackfoot River near Bonner, for example, peak flow dates average 10 days earlier than in the 1940s, and in 2023, 2024 and 2025, they were 21, 11 and 15 days (respectively) earlier than the 92-year median. In the same period (1940-2015), average August flows decreased by 201 cubic feet per second (cfs). This summer, Blackfoot River flows set a new all-time record low.
Warmer winters are “taxing” our snowpack bank account because more annual precipitation is falling as rain rather than snow. In the Blackfoot River basin, total annual precipitation hasn’t changed much, but the snowpack water equivalent (SWE), a measure of the total amount of liquid water stored in snowpack, has declined markedly. The three longest-running Snotel stations in the basin have measured SWE declines of 26%, 53% and 71% since the 1960s and 70s.
Economic inflation is a complex problem to which our nation has committed vigilance and developed the capacity to control. With the knowledge and tools we already have, we can solve the problem of rising global temperatures and address the mounting toll of adverse impacts in Montana and across the country.Tom Osborne is a professional hydrologist who over a 50-year career conducted hundreds of water resource projects across Montana, and in 2013 was recognized as a “Montana Water Legend” by his peers.
By Tom Osborne: September 30, 2025 – Bozeman, Mt
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