Modeling the Potential Areal Change of Permafrost Distribution in the Front Range of Colorado

Rock glacier topoclimatic variables (elevation and aspect) have been used to model modern and past permafrost distribution in major mountain ranges of the world. Warmer climates could cause permafrost zones to shrink and initiate slope instability hazards, thus modeling potential future change remains imperative. Past and future permafrost distribution in the Front Range of Colorado was examined by calibrating an existing permafrost model using a standard adiabatic rate for mountains (0.5°C per 100 m) for a 4°C range of cooler and warmer temperatures. According to the model, permafrost currently covers about 12% (326.1 km2) of the entire study area (2721.5 km2). In a 4°C cooler climate, 73.7% (2004.4 km2) of the study area could be covered by permafrost, whereas in a 4°C warmer climate, almost no permafrost would be found. Permafrost would be reduced severely by 93.9% (a loss of 306.2 km2) in a 2.0°C warmer climate; however, permafrost will likely respond slowly to change. Relict rock glacier distribution indicates that Mean Annual Air Temperature (MAAT) was once at least some 3.0 to 4.0°C cooler during the Pleistocene with permafrost extending some 600 to 700 m lower than today. The model is effective at identifying temperature sensitive areas for future monitoring; however, other feedback mechanisms such as precipitation are neglected.