The Disproportionate Effect of Uniform Warming on Mountain Snowpack
Abstract
Other factors being held constant, as air temperatures rise, mountains should become snow free progressively earlier in the water year. Indeed, based on SNOTEL snow water equivalent measurements and interpolated surface air temperatures from reanalysis, the change in water year day when a site become snow free ζ per degree of mean air temperature T are negative for every SNOTEL site in the Western US, (i.e., dζ/dT<0). However, the magnitudes of dζ/dT for these SNOTEL sites are also a function of the long-term mean temperature at each site ⟨ T ⟩ , with the magnitude of the sensitivity increasing at a growing rate for linearly increasing mean state temperature ⟨ T ⟩ .
What governs the functional relationship between dζ/dT and ⟨ T ⟩ ? In other words, for a given increase in air temperature, why are the warmest stations becoming snow free at a much greater rate than cooler stations? To address this question we develop a highly idealized model of snowpack and examine the effect of increasing temperature on the day when the model becomes snow free. Analysis of this model suggests that the dependency of dζ/dT on ⟨ T ⟩ emerges from the approximately sinusoidal characteristic of the annual cycle of temperature, and specifically the functional relationship between the number of warming days (days where site temperature is above zero) and T. These results demonstrate a mechanism by which uniform warming has a larger impact on the most vulnerable mountain regions. In other words, relatively warmer mountain regions experience a disproportionately shorter winter season than cooler areas for the same increase in air temperature.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C33C1583E
- Keywords:
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- 0736 Snow;
- CRYOSPHERE;
- 0740 Snowmelt;
- CRYOSPHERE;
- 0758 Remote sensing;
- CRYOSPHERE;
- 1863 Snow and ice;
- HYDROLOGY