Modeling past and future alpine permafrost distribution in the Colorado Front Range

Abstract

Rock glaciers, a feature associated with at least discontinuous permafrost, provide important topoclimatic information. Active and inactive rock glaciers can be used to model current permafrost distribution. Relict rock glacier locations provide paleoclimatic information to infer past conditions. Future warmer climates could cause permafrost zones to shrink and initiate slope instability hazards such as debris flows or rockslides, thus modeling change remains imperative. This research examines potential past and future permafrost distribution in the Colorado Front Range 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 per cent (326·1 km 2 ) of the entire study area (2721·5 km 2 ). In a 4°C cooler climate 73·7 per cent (2004·4 km 2 ) 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 per cent (a loss of 306·2 km 2 ) 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 600-700 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.

Future climate warming and changes to mountain permafrost in the Bolivian Andes

“…Conversely, rock glaciers are normally located in the upper part of the talus window, and with the talus window expected to move towards higher elevations with a changing climate, a reduction in the area available for talus production and rock glacier supply is to be expected. Just as importantly, rock glaciers are known to respond slowly to changes in temperature (Janke 2005), and so a time lag between observed temperature increase and rock glacier response is expected. However, there is little information on such lag times, and due to the complexity of the energy balance at glacier and permafrost surfaces, potential future changes can only be roughly estimated (Haeberli and Beniston 1998).…”

“…However, at regional scales it is strongly correlated with the Mean Annual Air Temperature (MAAT), with the 0°C isotherm often used to mark the lower elevational boundary (Del Barrio et al 1990;Avian and Kellerer-Pirklbauer 2012). Although it is expected that atmospheric warming will cause an upward shift in this lowest elevation boundary (Haeberli et al 1993;Janke 2005;Bonnaventure and Lewkowicz 2011), the coarse spatial resolution of current Global Climate Models (GCMs) does not permit a precise understanding of likely changes to future permafrost extent at the regional level, thereby preventing water resource managers adapting their policies to climate change (Hijmans et al 2005;Buytaert et al 2010). Downscaling these climate projections to an appropriate spatial resolution is therefore a necessary first step towards understanding climatic impacts of future global warming on permafrost water stores at the regional scale (Marengo et al 2010), after which appropriate adaptation policies can be formulated.…”

“…They are already considered to be important sources of water in montane, arid environments like the Chilean and Argentinean Andes (Croce and Milana 2002;Brenning 2005;Azócar and Brenning 2010), and may become more so as glaciers recede (Millar and Westfall 2008;Esper Angillieri 2009). While work modelling the implications of climate change on rock glaciers is limited, active rock glaciers have been used for modelling permafrost extents and changes in the North American Rocky Mountains (Janke 2005).…”

Thawing glacial and permafrost features contribute to nitrogen export from Green Lakes Valley, Colorado Front Range, USA

“…Bedrock in GLV is composed of Precambrian schists and gneisses, the Silver Plume quartz monzonite, and Audubon-Albion stock . Permafrost has been verified above 3,500 m on Niwot Ridge (Ives and Fahey 1971) and more recently near Green Lake 5 (GL5; Leopold et al 2008) and in the GL4 watershed (Janke 2005). In addition to ARK, three rock-glacier/blockfield sites have been sampled: an 8-ha lobate rock glacier (RG5) at the foot of the north-facing side of Kiowa Peak and two blockfield sites above GL4 (EN.4L and KIO.SW, Fig.…”

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

“…Changes in MAAT were simulated in the spatial model by uniformly increasing the values of equivalent elevation in the transformed DEM for cooling scenarios or decreasing them for warming scenarios (Janke, 2005;Bonnaventure and Lewkowicz, 2010), and then running the model to produce an altered BTS surface. This affects the predicted permafrost probabilities that are calibrated with the non-linear logistic regression coefficients determined for the 1971-2000 base case.…”