Abstract
Abstract. Mountain permafrost and rock glaciers in the dry Andes are of growing interest due to the increase in mining industry and infrastructure development in this remote area. Empirical models of mountain permafrost distribution based on rock glacier activity status and temperature data have been established as a tool for regional-scale assessments of its distribution; this kind of model approach has never been applied for a large portion of the Andes. In the present study, this methodology is applied to map permafrost favourability throughout the semi-arid Andes of central Chile (29–32° S), excluding areas of exposed bedrock. After spatially modelling of the mean annual air temperature distribution from scarce temperature records (116 station years) using a linear mixed-effects model, a generalized additive model was built to model the activity status of 3524 rock glaciers. A permafrost favourability index (PFI) was obtained by adjusting model predictions for conceptual differences between permafrost and rock glacier distribution. The results indicate that the model has an acceptable performance (median AUROC: 0.76). Conditions highly favourable to permafrost presence (PFI ≥ 0.75) are predicted for 1051 km2 of mountain terrain, or 2.7 % of the total area of the watersheds studied. Favourable conditions are expected to occur in 2636 km2, or 6.8 % of the area. Substantial portions of the Elqui and Huasco watersheds are considered to be favourable for permafrost presence (11.8 % each), while in the Limarí and Choapa watersheds permafrost is expected to be mostly limited to specific sub-watersheds. In the future, local ground-truth observations will be required to confirm permafrost presence in favourable areas and to monitor permafrost evolution under the influence of climate change.
Highlights
Mountain permafrost is widely recognized as a phenomenon that may influence slope stability (Kääb et al, 2005; Harris et al, 2009) and hydrological systems (Bommer et al, 2010; Caine, 2010; Haeberli, 2013), which poses a challenge to economic development in high mountains (Taillant, 2015)
Rock glaciers are most abundant in the Elqui (n = 681), Limarí (n = 486) and Huasco (n = 424) watersheds; in contrast, they are less abundant in Choapa watershed (n = 324)
In the Huasco and Elqui watersheds, nearly 50 % of all active rock glaciers are located at negative mean annual air temperature (MAAT); in contrast, in the Limarí and Choapa watersheds in the southern part of the study contain less than 20 % (Fig. 3)
Summary
Mountain permafrost is widely recognized as a phenomenon that may influence slope stability (Kääb et al, 2005; Harris et al, 2009) and hydrological systems (Bommer et al, 2010; Caine, 2010; Haeberli, 2013), which poses a challenge to economic development in high mountains (Taillant, 2015). Some cases of rock glacier destabilization have been observed in the Andes (Bodin et al, 2012), raising the question of sensitivity of ice-rich permafrost to climate warming. Empirical models describing the distribution of mountain permafrost based on geomorphological permafrost indicators and topographic and climatic predictors are a simple yet effective approach toward a first assessment of its distribution at a regional scale (Lewkowicz and Ednie, 2004; Janke, 2005; Boeckli et al, 2012a, b; Sattler et al, 2016). In the Andes, the boundaries of permafrost have been determined based on global climate models at coarse resolution scales (Gruber, 2012; Saito et al, 2015); regionally calibrated permafrost mapping based on geomorphological evidence has not been attempted previously in the Andes. The recent availability of accurate global digital elevation models (DEMs), the compilation of new rock glacier inventories, and the improved access to meteorological data provide a unique
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