Stable isotope compositions of precipitation from Gunnison, Colorado 2007-2016: implications for the climatology of a high-elevation valley.

Stable isotope ratios of precipitation are useful tracers of climatic and hydrological processes. To better understand the isotope hydro-climatology of a high-elevation Rocky Mountain valley we collected meteoric water samples from Gunnison, Colorado, USA and determined stable isotope values for 239 individual precipitation events over a nine year period. Annual precipitation in Gunnison is moderately bi-modal with significant winter snowfall and convective summer thunderstorms associated with the North American Monsoon. Stable isotope values of precipitation span a large range, with summer rains as high as δH = +19‰ and δO = +4.8‰ (relative to V-SMOW) and winter snowfall as low as δH = -286‰ and δO = -36.7‰. These data define a local meteoric water line for Gunnison of δH = 7.2 δO - 4.2. Monthly meteoric water lines have slopes similar to the Global Meteoric Water Line (∼8) for winter months and more evaporated slopes (∼6) during the summer. Monthly mean temperature most strongly controls the monthly isotopic composition of precipitation (m = 0.61-0.64 ‰/°C); the slope of the isotope/temperature relationship is steeper in summer than winter.