Dry Andes Research Articles

Effect of shade and precipitation on germination and seedling establishment of dominant plant species in an Andean arid region, the Bolivian Prepuna.

Germination and seedling establishment are two critical processes in the life cycle of plants. Seeds and seedlings must pass through a series of abiotic and biotic filters in order to recruit as members of their communities. These processes are part of the regeneration niche of the species. In arid regions, the regeneration niche is frequently associated to facilitation by shade. Facilitation is a positive interaction between plants, in which one of them acts as a benefactor (the nurse) of the other (the beneficiary). The result of this interaction can be reflected in the increased growth, survival, and/or reproduction of the beneficiary plant. In this study, we determined experimentally the effect of shade and irrigation on the germination and early survival of dominant species of a semi-arid Andean region, the Bolivian Prepuna. An experiment with Acacia feddeana, Prosopis ferox, Cercidium andicola (woody species), Parodia maassii, and Oreocereus celsianus (cactus species) was carried out at an experimental garden in La Paz, Bolivia, with a bifactorial design, considering shaded and unshaded pots, subjected to two irrigation treatments (≈50 and 80 mm of rainfall during the whole study period). Microenvironmental conditions did not affect the seed germination of the woody species. However, they showed differences in seedling survival: A. feddeana survived better under shade, whereas P. ferox and C. andicola survived better without shade. Cercidium andicola, compared to P. ferox, was more affected by shade and low irrigation. Although germination success of cacti was low, both species germinated better under shade and with high irrigation. These results showed differences in the regeneration niche of dominant species of the Prepuna which may favor their coexistence and which may be characteristic of other dry Andean regions.

Ice content and interannual water storage changes of an active rock glacier in the dry Andes of Argentina

Abstract. The quantification of volumetric ice and water content in active rock glaciers is necessary to estimate their role as water stores and contributors to runoff in dry mountain catchments. In the semi-arid to arid Andes of Argentina, active rock glaciers potentially constitute important water reservoirs due to their widespread distribution. Here however, water storage capacities and their interannual changes have so far escaped quantification in detailed field studies. Volumetric ice and water content was quantified using a petrophysical four-phase model (4PM) based on complementary electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) in different positions of the Dos Lenguas rock glacier in the upper Agua Negra basin, Argentina. We derived vertical and horizontal surface changes of the Dos Lenguas rock glacier, for the periods 2016–2017 and 2017–2018 using drone-derived digital elevation models (DEMs). Interannual water storage changes of −36 mm yr−1 and +27 mm yr−1 derived from volumetric surface changes for the periods 2016–2017 and 2017–2018, respectively, indicate that significant amounts of annual precipitation can be stored in and released from the active rock glacier. Geophysical results show heterogeneous ice and water content with ice-rich permafrost and supra-, intra- and sub-permafrost water pathways at the end of the thaw period. Active layer and ice-rich permafrost control traps and pathways of shallow groundwater and thus regulate interannual storage changes and water releases from the active rock glaciers in the dry mountain catchment. The ice content of 1.7–2.0 × 109 kg in the active Dos Lenguas rock glacier represents an important long-term ice reservoir, as do other ground ice deposits in the vicinity, if compared to surface ice that covers less than 3 % of the high mountain catchment.

Turnover, richness difference and nestedness of rodent assemblages along the southern Andes elevation gradient

AbstractBeta diversity in ecological communities can reflect adaptations of species to differences in climate, environmental characteristics and site history, as well as local ecological dynamics. These dissimilarities among communities may reflect different processes as species replacement and richness difference or nestedness, which can be generated by different factors. Assemblages in mountain regions are expected to exhibit high beta diversity due to sharp environmental variation and historical events promoting isolation. Diversity patterns of small mammals along elevation gradients in the southern dry Andes exhibit high richness among high elevations and a humped shape pattern for abundances. However, it is not clear how beta diversity changes along this gradient, or the processes involved in this variation. Here we aim to evaluate small mammal beta diversity patterns along the elevation gradient. Therefore, we decomposed beta diversity into spatial turnover, richness differences and richness differences as a result of nestedness. Assemblage structure variation was assessed qualitatively and quantitatively. Also, we evaluate the local contribution of beta diversity (LCBD) and species contribution to beta diversity, to identify priority conservation sites and species. Our results show contrasting patterns among qualitative and quantitative beta diversity components. The former was mainly explained by species turnover, while the latter showed a higher contribution of richness difference than species turnover. Most components of beta diversity decreased with elevation, except for abundance turnover that showed an opposite trend. Furthermore, LCBD was higher at lower and mid‐elevation sites and exhibited a negative relationship with species richness and abundance.

Identificación de clústeres glaciares a lo largo de los Andes chilenos usando variables topoclimáticas

Utilizando variables topográficas y climáticas, presentamos clústeres glaciares en los Andes chilenos (17.6-55.4°S), donde se ejecutó el algoritmo de aprendizaje automático no supervisado Partitioning Around Medoids (PAM). Los resultados clasificaron 23,974 glaciares dentro de trece clústeres, que muestran condiciones específicas en términos de cantidades anuales y mensuales de precipitación, temperatura y radiación solar. En los Andes secos, los valores medios anuales de cinco clústeres glaciares (C1-C5) muestran una diferencia de precipitación y temperatura de hasta 400 mm (29 y 33°S) y 8°C (33°S), con una resta de elevación promedio de 1800 m entre glaciares clústeres C1 y C5 (18 a 34°S). Mientras que en los Andes húmedos las mayores diferencias se observaron en la latitud del Campo de Hielo Patagónico Sur (50°S), donde los valores medios anuales de precipitación y temperatura muestran una precipitación marítima por encima de 3700 mm/año (C12), donde el aire húmedo occidental juega un papel importante, y por debajo de 1000 mm/año al este del Campo de Hielo Patagónico Sur (C10), con diferencias de temperatura cercanas a 4°C y una resta de elevación promedio de 500 m. Esta clasificación confirma que los glaciares chilenos no pueden agruparse solo latitudinalmente, contribuyendo a una mejor comprensión de los cambios recientes en el volumen de los glaciares a escala regional.

Phyllocnistis furcata sp. nov.: a new species of leaf-miner associated with Baccharis (Asteraceae) from Southern Peru (Lepidoptera, Gracillariidae).

The southwestern Andes of Peru harbors a hidden taxonomic diversity of Lepidoptera. Here a new leaf-mining species of Gracillariidae (Lepidoptera) is described, Phyllocnistis furcata Vargas & Cerdeña, sp. nov., from a dry Andean valley of southern Peru, at 2400 m above sea level. The morphological aspects of adults (male and female) and the immature stages associated with Baccharis alnifolia Meyen & Walp. (Asteraceae) are given, under optical microscopy and scanning electron microscopy. DNA barcodes show that its nearest neighbor is the Atlantic Forest species Phyllocnistis ourea Brito & Moreira, 2017 that feeds on Baccharis anomala DC. The importance of morphological characters from immature stages for diagnosis among congeneric species is also discussed. Phyllocnistis furcata represents the fourth species of Phyllocnistis Zeller for Peru, and first record from the south of Peru for the genus.

Isotopic composition and hydrogeochemistry of a periglacial Andean catchment and its relevance in the knowledge of water resources in mountainous areas

ABSTRACT Glacial and periglacial basins contain the largest reserves of fresh water in the world. These areas are extremely sensitive to global warming and climate change. The dry Andes of South America are characterized by large periglacial areas. This study focuses on the water isotopic composition and hydrochemistry of a typical periglacial environment of the Andes, in the Vallecitos catchment (2400–5500 m a.s.l.), Cordillera Frontal, Argentina. Detailed fieldwork was conducted between 2013 and 2017 with 240 samples collected for major ions and physicochemical parameters, and 67 samples analysed for 2H and 18O. The chemical composition of precipitation is typical Ca-HCO3, while streams and groundwaters are Ca-MgSO4 type. The isotope content of precipitation shows a wide dispersion. The snow samples are in general more depleted than the rainfall. Some springs vary their composition seasonally, associated to the melting of perennial snow patches. In general, all samples from the upper basin present depleted isotope contents related to recharge at higher altitudes, whereas samples from the lower basin show more enriched values. Intermediate compositions reflect the melting of snow and degrading ice-rich permafrost. These results will give a better understanding of the dynamics of water to manage water resources.

Chronology of Miocene terrestrial deposits and fossil vertebrates from Quebrada Honda (Bolivia)

At ~3500 m above sea level in the Eastern Andean Cordillera, Quebrada Honda Basin exposes more than 300 m of middle Miocene sedimentary strata, developed on distal alluvial fan sediments interstratified with volcanoclastic deposits, overlying Paleozoic basement. These deposits are rich in exotic vertebrate fauna adapted to a wetter and warmer climate at lower paleoelevation, as contrasted with the present high-elevation cold and dry Andean conditions. This study provides new magnetostratigraphic and 40Ar/39Ar age control of the Quebrada Honda, Río Rosario and Huayllajara fossiliferous areas, demonstrating that they are 13.1–12.4 Ma. Part of the succession evidences cyclical deposition of calcretes and reddish mudstones which may be a response to precessional orbital-forcing climatic processes. Paleomagnetic measurements show a significant clockwise tectonic rotation related to postdepositional tectonism, associated with evidence of an important uplift after the deposition of Quebrada Honda sediments. This uplift of the Andean Eastern Cordillera was associated with the formation of the Subandean fold-thrust belt and the development of the Amazon and La Plata drainage basins. Proposed uplift rates of >200 m/Ma are compatible with well-established rates of uplift recorded in contemporaneous alpine sections.

Late Holocene dynamics of the south American summer monsoon: New insights from the Andes of northern Chile (21°S)

The South American summer monsoon (SASM) is the most important climate system of tropical South America, transporting moisture from the tropical Atlantic Ocean to the core of the continent during the austral summer. Recent paleoclimate studies suggest that past variability of the SASM has been more heterogenous in space and time than previously thought, implying that different atmospheric drivers controlled its long-term evolution. Unfortunately, past SASM reconstructions are largely limited to the last 2000 years and mainly focused on the core of the monsoon domain where precipitation does not fall exclusively during the monsoon season, thereby limiting our understanding of its long-term changes, drivers and mechanisms. Here we present a new 4000-year SASM precipitation reconstruction based on a high-resolution pollen sequence from a mountain lake in the dry Andes of northern Chile (21°S). We provide evidence for two centennial-scale intervals of enhanced SASM precipitation between 4000–3400 and 2300-1900 cal yr BP. These intervals are replicated in records from the southern portion of the central Andes (>18°S) but not clearly detected further north, suggesting the existence of a monsoon dynamics largely decoupled from latitudinal shifts of the Intertropical Convergence Zone. A comparison with precipitation reconstructions from the entire SASM domain and modern climate datasets suggests a teleconnection with the Southern Hemisphere circulation through the intensification of the South Atlantic Convergence Zone and/or the intrusion of extra-tropical Atlantic moisture. Our results highlight that significant spatial and temporal variability of the SASM occurred during the most recent millennia, and therefore social and environmental forecast should consider that similar variations will likely occur in the future.

Land suitability projections for traditional sub-alpine cropping in the Australian Alps and Chilean Dry Andes. A combined biophysical and irrigation potential perspective

A GIS-based multi-criteria approach is applied in the Upper Murray River basin (Australian Alps) and Rapel River basin (Chilean Dry Andes) to project both biophysical and irrigation potential land suitability. Agricultural adaptation guidelines are then suggested in the context of agricultural expansion, land use change and water management. The findings show, first, the orographic hydro-climate patterns are the primary control over land suitability, its uncertainty and sensitivity. Second, the expected land suitability reduction during the 21st century will be driven primarily by catchment-level irrigation potential deficits even over the declining farm-level biophysical conditions. Third, a distinctive functionality for flatter and steeper agricultural systems is likely to be identifiable from land suitability trajectories. Further applications should be focused on regional-type studies and improvements regarding the effectiveness of expert judgement, validation, non-linear/daily dynamics and the influence of extreme climatology on land suitability.

Permafrost model in coarse-blocky deposits for the Dry Andes, Argentina (28°-33° S)

In this work, a statistical permafrost distribution model for coarse-blocky deposits in the Dry Andes of Argentina (28-33°S) is presented. The empiric mathematical formulation was based on a logistic regression. The final model is a combination of two independent occurrence probability models: a) a mean annual air temperature-terrain ruggedness model and, b) a mean annual air temperature-potential incoming solar radiation model. For all cases, calibration was made according the complete geomorphological characterization of a periglacial basin with 250 km2. Lately, the results of probabilistic model were extrapolated to the whole study area in the Dry Andes and compared with the Argentine rock glacier inventory data base. High permafrost likelihood, in coarse debris, is expected above 4200 and 5700 m a.s.l., from south to north in the study area and covers a surface of approximately 1200 km2. Medium permafrost likelihood is expected above 3400 and 4200 m a.s.l. with a surface of 6178 km2 while low permafrost likelihood, occurs between 3000 and 3400 m a.s.l. with an area of 11.060 km2. These findings indicate that permafrost may occur in several types of coarse-blocky deposits in the Dry Andes, not only restricted to rock glaciers. Thermal properties of the ground in coarse-blocky deposits allow permafrost permanence, even under unfavourable climatic conditions.The performance of the permafrost model was also tested, considering the transition from cold paleoclimate Tardiglacial to present climatic conditions. During the warming, likely permafrost surface reduced from 56 to 13%. In the same way, rock glaciers with high and medium permafrost likelihood decrease from 62 to 30%, respectively while, rock glaciers with low likelihood and no permafrost category, increased 75% and 474%, respectively. Moreover, we identified some sites in which permafrost degradation is arguably expected. About that, 0.9% of the rock glaciers in the study area display possible permafrost degradation and 33% of them, likely permafrost degradation.

Debris flow susceptibility mapping using frequency ratio and seed cells, in a portion of a mountain international route, Dry Central Andes of Argentina

Debris flow and floods represent one of the main natural hazards that impact transport infrastructure, causing serious damage, economic losses and hinder regional economic development. These processes are eventually associated with massive traffic cuts and direct damage to road structures. To enable the prevention of such consequences, this paper employs statistical modeling techniques, various instability factors and geomorphological mapping to generate debris flow susceptibility maps in a portion of an important route on the Dry Andes of San Juan in the Agua Negra River basin, Argentina. A debris flows inventory map was prepared using satellite images and field checks. The debris flows inventory was randomly divided into a model dataset 80% (47 debris flows) and remaining 20% (12 debris flows) data was used for validation purpose. The instability factors chosen that influence debris flows occurrence were: elevation, slope angle, slope aspect, solar radiation, topographic wetness index, stream power index, topographic position index, Melton ruggedness number, terrain ruggedness index, sediment transport capacity index, plan curvature, profile curvature, lithology, distance to road and proximity to stream. Using these factors, six different models of debris flow susceptibility were calculated by Frequency ratio (Fr). Lithology (igneous complex) was found to be important debris flows-related factor in the study area. The precision of the results was evaluated by receiver operating characteristic (ROC) analysis. According to the area under the curve (AUC) the models of all flow track and natural breaks and all flow track and geometrical interval were 0.83 and 0.84, respectively, showing a practically identical predictive capacity.

Two decades of glacier mass loss along the Andes

Andean glaciers are among the fastest shrinking and largest contributors to sea level rise on Earth. They also represent crucial water resources in many tropical and semi-arid mountain catchments. Yet the magnitude of the recent ice loss is still debated. Here we present Andean glacier mass changes (from 10° N to 56° S) between 2000 and 2018 using time series of digital elevation models derived from ASTER stereo images. The total mass change over this period was −22.9 ± 5.9 Gt yr−1 (−0.72 ± 0.22 m w.e. yr−1 (m w.e., metres of water equivalent)), with the most negative mass balances in the Patagonian Andes (−0.78 ± 0.25 m w.e. yr−1) and the Tropical Andes (−0.42 ± 0.24 m w.e. yr−1), compared to relatively moderate losses (−0.28 ± 0.18 m w.e. yr−1) in the Dry Andes. Subperiod analysis (2000–2009 versus 2009–2018) revealed a steady mass loss in the tropics and south of 45° S. Conversely, a shift from a slightly positive to a strongly negative mass balance was measured between 26 and 45° S. In the latter region, the drastic glacier loss in recent years coincides with the extremely dry conditions since 2010 and partially helped to mitigate the negative hydrological impacts of this severe and sustained drought. These results provide a comprehensive, high-resolution and multidecadal data set of recent Andes-wide glacier mass changes that constitutes a relevant basis for the calibration and validation of hydrological and glaciological models intended to project future glacier changes and their hydrological impacts. Glaciers in the Andes have lost about 23 Gt of mass per year between 2000 and 2018, with the fastest loss in Patagonia, according to time series of digital elevation models that are based on ASTER stereo images.

Nieves penitentes are a new habitat for snow algae in one of the most extreme high-elevation environments on Earth

ABSTRACTNieves penitentes are pinnacle-shaped ice structures found at high elevations in the dry Andes. Here we report, using molecular and microscopic approaches, the first description of snow algae communities inhabiting penitente ice at 5,277 m a.s.l., demonstrating a new habitat for snow algae in one of the most extreme environments on Earth. Red ice patches on penitentes contained a microbial community dominated by algae in the genera Chlamydomonas and Chloromonas, both of which were closely related to known snow algae from alpine and polar environments. In contrast, we obtained few snow algae sequences from clear ice, but we did find cyanobacteria sequences and evidence of aeolian-deposited organic matter. Tephra (“soil”) within and just downhill from the penitente field hosted more complex bacterial and eukaryotic communities that were significantly different from ice communities in terms of both alpha and beta diversity. In this environment penitentes provide both water and shelter from harsh winds, high UV radiation, and thermal fluctuations, creating an oasis in an otherwise extreme landscape. Intriguingly, recent planetary investigations have suggested the existence of penitente-like structures on other planetary bodies of our solar system. Therefore, penitentes and the harsh environment that surrounds them provide a new terrestrial analog for astrobiological studies of life beyond Earth.

Intraspecific interactions affect the spatial pattern of a dominant shrub in a semiarid shrubland: A prospective approach

Dispersal, physical conditions and biotic interactions contribute to determine the spatial distribution of individuals in plant populations. Much of what we know has been learned from studies that retrospectively posit mechanisms presumed to have generated the observed spatial patterns. Here we present a prospective approach. We start by measuring spatial demographic effects and evaluate if they can generate observed spatial patterns. We evaluated the influence of interactions among conspecifics on vital rates, demography and spatial distribution of Croton aff. wagneri, a dominant shrub in dry Andean ecosystems. Recruitment, survival and growth varied in relation with distance to conspecifics neighbours and with their summed cover. We built a spatial individual‐based model and simulated its population dynamics in 30 × 30 m plots for a 30‐year period. We compared the predicted spatial pattern from these demographic models with that observed among plants in 16 independent plots with the same area. Simulated populations mimicked observed spatial patterns, although in plots at high elevations the simulated populations did not reproduce the observed inhibition at small scales. Observed and simulated patterns indicated differences between elevations in maximum aggregation and location of the distances with higher aggregation. We discuss how consideration of critical seed and juvenile stages and interspecific interactions could further improve our understanding of spatial pattern and recommend that these factors be considered in future models.

Discontinuities in quinoa biodiversity in the dry Andes: An 18-century perspective based on allelic genotyping.

History and environment shape crop biodiversity, particularly in areas with vulnerable human communities and ecosystems. Tracing crop biodiversity over time helps understand how rural societies cope with anthropogenic or climatic changes. Exceptionally well preserved ancient DNA of quinoa (Chenopodium quinoa Willd.) from the cold and arid Andes of Argentina has allowed us to track changes and continuities in quinoa diversity over 18 centuries, by coupling genotyping of 157 ancient and modern seeds by 24 SSR markers with cluster and coalescence analyses. Cluster analyses revealed clear population patterns separating modern and ancient quinoas. Coalescence-based analyses revealed that genetic drift within a single population cannot explain genetic differentiation among ancient and modern quinoas. The hypothesis of a genetic bottleneck related to the Spanish Conquest also does not seem to apply at a local scale. Instead, the most likely scenario is the replacement of preexisting quinoa gene pools with new ones of lower genetic diversity. This process occurred at least twice in the last 18 centuries: first, between the 6th and 12th centuries—a time of agricultural intensification well before the Inka and Spanish conquests—and then between the 13th century and today—a period marked by farming marginalization in the late 19th century likely due to a severe multidecadal drought. While these processes of local gene pool replacement do not imply losses of genetic diversity at the metapopulation scale, they support the view that gene pool replacement linked to social and environmental changes can result from opposite agricultural trajectories.

DInSAR for a Regional Inventory of Active Rock Glaciers in the Dry Andes Mountains of Argentina and Chile with Sentinel-1 Data

The Dry Andes region of Argentina and Chile is characterized by a highly developed periglacial environment. In these arid or semi-arid regions, rock glaciers represent one of the main pieces of evidence of mountain creeping permafrost and water reserves in a solid state. However, their distribution, degree of activity, and response to global warming are not yet well understood. In this context, this work aims to show the potential of the Sentinel-1-based interferometric technique (DInSAR) to map active rock glaciers at a regional level. In particular, the paper presents an active rock glacier inventory for the study area, which covers approximately 40,000 km2, ranging from latitude 30°21′S to 33°21′S. A total of 2116 active rock glaciers have been detected, and their elevations show a high correlation with the west-east direction. This result was obtained by using only 16 interferometric pairs. Compared to other remote sensing classification techniques, the interferometric technique offers a means to measure surface displacement (active rock glacier). This results in a reliable classification of the degree of activity compared to other methods, based on geomorphological, geomorphometric, and/or ecological criteria. This work presents evidence of this aspect by comparing the obtained results with existing optical data-based inventories. We conclude that the combination of both types of sensors (radar and optical) is an appropriate procedure for active rock glacier inventories, as both mapping methodologies are complementary.

An evaluation of physical and mechanical scarification methods on seed germination of Vachellia macracantha (Humb. & Bonpl. ex Willd.) Seigler & Ebinger

Los bosques secos andinos son ecosistemas con alta diversidad de flora y fauna y tienen alto riesgo de extinción debido a la presión de la actividad humana. V. macracantha es una especie nativa del bosque seco andino que tiene potencial para la reforestación y también brinda beneficios en sistemas agroforestales, debido a su capacidad de fijación de nitrógeno, el suministro de materia orgánica, la producción de sombra y protección del viento. La propagación de esta especie es limitada debido al bajo porcentaje de germinación de las semillas, las cuales presentan dormancia. El propósito de esta investigación fue determinar el método de escarificación más eficaz para la germinación de las semillas de V. macracantha. Dos tipos de métodos fueron probados, la inmersión en ácidos fuertes (escarificación química), y la remoción de la corteza de la semilla a través del limado, corte y remojo en agua caliente (escarificación física). Se utilizó un diseño de bloques completamente al azar con 3 repeticiones. Para los métodos químicos, se usó ácido sulfúrico, nítrico, y fosfórico (50% v/v) a diferentes tiempos de exposición: 5, 10, 15, 20 y 25 minutos, respectivamente. Se midieron tres variables como sigue: porcentaje de germinación, la cantidad de hojas y la altura de la planta. Los métodos químicos no presentaron ninguna diferencia significativa en el porcentaje de germinación. El método físico de limado de la semilla tuvo el porcentaje más alto de germinación con un 46%, en comparación al control que tuvo el 6%. Ningún tratamiento tuvo diferencias significativas en los parámetros de cantidad de hojas y la altura de la planta.

Across the Arid Diagonal: deglaciation of the western Andean Cordillera in southwest Bolivia and northern Chile

Here we review published cosmogenic records of glaciation and deglaciation from the western cordillera of the arid subtropical Andes of northern Chile and southwest Bolivia. Specifically, we examine seven published studies describing exposure ages from moraines and glaciated bedrock spanning the glaciological Arid Diagonal, the region of the dry Andes where there is no clear evidence for glaciation over at least the last global glaciation. We also present new cosmogenic 36Cl exposure ages from two previously undated sets of moraines in the deglaciated region near 22ºS. Taken together, these records indicate that the most extensive regional glaciation occurred ca. 35-45 ka, followed by slow, punctuated retreat through the global last glacial maximum, and rapid retreat after ~15-17 ka. In the vicinity of the large Altiplanic lakes that existed during the late glacial stage, the 15-17 ka moraines overrode the earlier moraines, whereas elsewhere regionally, on both sides of the Arid Diagonal, late glacial wet periods are represented only by less-prominent moraines in more retracted positions.

Permafrost distribution modelling in the semi-arid Chilean Andes

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.

Hydrological Modeling of Highly Glacierized Basins (Andes, Alps, and Central Asia)

The Soil and Water Assessment Tool (SWAT) was used to simulate five glacierized river basins that are global in coverage and vary in climate. The river basins included the Narayani (Nepal), Vakhsh (Central Asia), Rhone (Switzerland), Mendoza (Central Andes, Argentina), and Central Dry Andes (Chile), with a total area of 85,000 km2. A modified SWAT snow algorithm was applied in order to consider spatial variation of associated snowmelt/accumulation by elevation band across each subbasin. In previous studies, melt rates varied as a function of elevation because of an air temperature gradient while the snow parameters were constant throughout the entire basin. A major improvement of the new snow algorithm is the separation of the glaciers from seasonal snow based on their characteristics. Two SWAT snow algorithms were evaluated in simulation of monthly runoff from the glaciered watersheds: (1) the snow parameters are lumped (constant throughout the entire basin) and (2) the snow parameters are spatially variable based on elevation bands of a subbasin (modified snow algorithm). Applying the distributed SWAT snow algorithm improved the model performance in simulation of monthly runoff with snow-glacial regime, so that mean RSR decreased to 0.49 from 0.55 and NSE increased to 0.75 from 0.69. Improvement of model performance was negligible in simulations of monthly runoff from the basins with a monsoon runoff regime.