Mariano H. Masiokas

Snowpack Variations in the Central Andes of Argentina and Chile, 1951–2005: Large-Scale Atmospheric Influences and Implications for Water Resources in the Region

Abstract The snowpack in the central Andes (30°–37°S) is the primary source for streamflow in central Chile and central-western Argentina, but few published studies are available on snowpack variability in the region. This paper develops the first regional snowpack series (1951–2005) from Chilean and Argentinean snow course records. This series shows a strong regional signal, marked interannual variability, and a positive, though nonsignificant, linear trend. Correlations with local precipitation and temperature records reveal a marked association with conditions in central Chile. High snow accumulation is generally concurrent with El Nino events in the tropical Pacific, but only 5 of the 10 driest years coincided with La Nina events. Evaluation of 500-hPa geopotential height anomaly maps during extreme snow years highlights the crucial significance of tropospheric conditions in the subtropical and southeast Pacific in modulating snowfall. Correlations with gridded SST and SLP data and multiple regression...

Climatic significance of intra-annual bands in the wood of Nothofagus pumilio in southern Patagonia

Nothofagus pumilio (Poepp et Endl.) Krasser is the dominant subalpine tree in the southern Andes between 36°S and 55°S. Increment cores from a N. pumilio stand growing near the Ameghino Glacier (50°25′S, 73°10′W), southern Patagonian Andes, Argentina, contain significant numbers of intra-annual bands (or false rings) which have not been previously described for this species. These samples are used to develop a well-replicated ring-width chronology and a record of intra-annual bands from AD 1760 to 1997. Annual variations in radial growth of N. pumilio at this site are negatively correlated with spring–summer temperatures and positively with spring precipitation. The formation of intra-annual bands appears to be a response to anomalously dry-warm springs followed by wet-warm late summers. Intra-annual bands may occur in up to 95% of the sampled trees in a given year, and the percentage of trees affected was used as an indication of the strength of the forcing event. Narrow rings occurred in the years following intra-annual band formation, reflecting the lagged effect of unfavorable climatic conditions on tree growth during the subsequent growing season. Intra-annual bands occurred more frequently in the twentieth century than the late eighteenth and nineteenth centuries. This contrasting pattern seems to be a response to the combination of a long-term warming trend and a significant decrease in precipitation recorded during the last 100 years in this region of southern South America.

Intra- to Multidecadal Variations of Snowpack and Streamflow Records in the Andes of Chile and Argentina between 30° and 37°S

Abstract In a recent study the authors developed the first regionally averaged, transnational records of snowpack and streamflow for the Andes between 30° and 37°S using Chilean and Argentinean data. That study was mainly intended to evaluate the relationships between the interannual variations in the regional snowpack record and large-scale atmospheric variables and indices. Here the focus is on the main intra- to multidecadal variations in updated records of winter snowpack and mean annual river flows. River discharges show similar temporal variations on both sides of the Andes with extreme dry conditions concentrated between the mid-1940s and 1976/77 and extreme wet conditions peaking between the late 1970s and the 1980s. A regional streamflow composite (1906–2007) has a nonsignificant negative trend but significant regime shifts in 1945, when mean levels dropped 31%, and in 1977 when they increased 28%. These events coincide almost exactly with well-known shifts in the Pacific decadal oscillation (PDO...

Biogeographical Consequences of Recent Climate Changes in the Southern Andes of Argentina

Long-term trends of temperature variations across the Southern Andes (37–55°S) have been recently examined using a combination of instrumental and proxy records. Tree-ring based reconstructions indicate that the annual temperatures during the 20th century have been anomalously warm across the Southern Andes in the context of the past four centuries. The mean annual temperatures for northern and southern Patagonia during the interval 1900–1990 are 0.53°C and 0.86°C above the AD 1640–1899 means, respectively. Increased temperatures are seriously impacting the physical and biological systems across the Southern Andes.

Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across the Western Americas

Common patterns of climatic variability across the Western Americas are modulated by tropical and extra-tropical oscillatory modes operating at different temporal scales. Interannual climatic variations in the tropics and subtropics of the Western Americas are largely regulated by El Nino-Southern Oscillation (ENSO), whereas decadal-scale variations are induced by long-term Pacific modes of climate variability such as the Pacific Decadal Oscillation (PDO). At higher latitudes, climate variations are dominated by oscillations in the Annular Modes (the Arctic and Antarctic Oscillations) which show both interannual and longer-scale temporal oscillations. Here we use a recently-developed network of tree-ring chronologies to document past climatic variations along the length of the Western Cordilleras. The local and regional characterization of the relationships between climate and tree-growth provide the basis to compare climatic variations in temperature- and precipitation-sensitive records in the Western Americas over the past 3–4 centuries. Upper-elevation records from tree-ring sites in the Gulf of Alaska and Patagonia reveal the occurrence of concurrent decade-scale oscillations in temperature during the last 400 years modulated by PDO. The most recent fluctuation from the cold- to the warm-phase of the PDO in the mid 1970s induced marked changes in tree growth in most extratropical temperature-sensitive chronologies in the Western Cordilleras of both Hemispheres. Common patterns of interannual variations in tree-ring chronologies from the relatively-dry subtropics in western North and South America are largely modulated by ENSO. We used an independent reconstruction of Nino-3 sea surface temperature (SST) to document relationships to tree growth in the southwestern US, the Bolivian Altiplano and Central Chile and also to show strong correlations between these regions. These results further document the strong influence of SSTs in the tropical Pacific as a common forcing of precipitation variations in the subtropical Western America during the past 3–4 centuries. Common patterns of interdecadal or longer-scale variability in tree-ring chronologies from the subarctic and subantarctic regions also suggest common forcings for the annular modes of high-latitude climate variability. A clear separation of the relative influence of tropical versus high-latitude modes of variability is currently difficult to establish: discriminating between tropical and extra-tropical influences on tree growth still remains elusive, particularly in subtropical and temperate regions along our transect. We still need independent reconstructions of tropical and polar modes of climate variability to gain insight into past forcing interactions and the combined effect on climates of the Western Americas. Finally, we also include a series of brief examples (as ‘boxes’) illustrating some of the major regional developments in dendrochronology over this global transect in the last 10 years.

First Glacier Inventory and Recent Changes in Glacier Area in the Monte San Lorenzo Region (47°S), Southern Patagonian Andes, South America

Abstract We present the first glacier inventory of the Monte San Lorenzo region (47°35′S, 72°18′W) in the southern Patagonian Andes of Chile and Argentina. This region contains the largest and easternmost glaciers at these latitudes in South America. The inventory was developed using a combination of ASTER and Landsat ETM + scenes from 2005 and 2008, respectively, and a semi-automatic band ratio approach to map glacier ice. Manual corrections were applied to include debris-covered ice and ice in cast shadows. We inventoried 213 glaciers that cover a 2005/2008 total area of ca. 207 km2 and lie between 520 m and 3700 m in elevation. Landsat TM images acquired in 1985 and 2000 were subsequently used to assess changes in glacierized area over the 1985–2008 interval. Based on all available information, we determined an 18.6% reduction in the total glacier area since 1985. Glaciers smaller than 1 km2 have shown highly variable (0–100%) relative areal reduction, whereas the formation and growth of proglacial lakes promoted rapid recession of the larger valley glaciers, which concentrate the major ice losses, representing ca. 32% of the total glacier area reduction. Glacier fragmentation has occurred for 50% of the ice bodies larger than 1 km2. These results agree with the generalized pattern of glacier retreat observed throughout the Patagonian Andes, but the lack of detailed meteorological and glaciological data in the area preclude a more refined analysis of the climate-glacier relationships and processes explaining the recent glacier trends.

Spatiotemporal Variations in Hydroclimate across the Mediterranean Andes (30°–37°S) since the Early Twentieth Century

AbstractIn the Mediterranean Andes region (MA; 30°–37°S), the main rivers are largely fed by melting snowpack and provide freshwater to around 10 million people on both sides of the Andes Mountains. Water resources in the MA are under pressure because of the extensive development of industrial agriculture and mining activities. This pressure is increasing as the region faces one of its worst recorded droughts. Previous studies have pointed to El Nino–Southern Oscillation (ENSO) as the main climatic force impacting the MA. However, the role of decadal and multidecadal climate variability, their spatial patterns, and the recurrence of long-term droughts remains poorly studied. In an attempt to better understand these factors, spatial and temporal patterns of hydroclimatic variability are analyzed using an extensive database of streamflow, precipitation, and snowpack covering the period between 1910 and 2011. These analyses are based on the combination of correlation, principal components, and kernel estimat...

Rock Glaciers in the Patagonian Andes: An Inventory for the Monte San Lorenzo (Cerro Cochrane) Massif, 47° S

Abstract Although rock glaciers in the Central and Desert Andes of Argentina and Chile have been previously studied in detail, much less attention has been paid to the occurrence of these permafrost forms in Patagonia. Recently, however, the establishment of the Argentinean Glacier Inventory program, which intends to inventory and monitor all ice masses along the Argentinean Andes, has started a large amount of new geocryological research. The project is designed to provide reliable and worldwide comparable results, supported by well established technical procedures and background information. Presented here is the first rock glacier inventory of the Monte San Lorenzo (Cerro Cochrane) region in the southern Patagonian Andes. A total of 130 intact (9.86 km2) and 47 fossil (1.45 km2) landforms were inventoried using two 2.5 m resolution ALOS Panchromatic Remote‐sensing Instruments for Stereo Mapping images. Since the Argentinean federal initiative described above legally protects all rock glaciers in the country as water reserves, and due to the little scientific knowledge concerning rock glaciers in the vast majority of the Patagonian Andes, this inventory provides an important basis for political decision‐making and opens further geocryological research avenues for the Patagonian region in general.

Geometric evolution of the Horcones Inferior Glacier (Mount Aconcagua, Central Andes) during the 2002–2006 surge

The Central Andes of Chile and Argentina (31–35°S) contain a large number and variety of ice masses, but only two surging glaciers have been studied in this region. We analyzed the 2002–2006 surge of the Horcones Inferior Glacier, Mount Aconcagua, Argentina, based on medium spatial resolution (15–30 m) satellite images and digital elevation models. During the buildup phase the glacier was stagnant, with velocities lower than 0.1 m/d. In the active-phase velocities reached 14 m/d and the glacier front advanced 3.1 km. At the peak of the active phase (2003–2004), the area-averaged elevation change was −42 m in the reservoir zone (2.53 km2) and +30 m in the receiving zone (3.31 km2). The estimated ice flux through a cross section located at 4175 meter above sea level was 108 m3 during a period of 391 days, a flux that suggests a mean glacier thickness at this location of ~90 m. The depletion phase showed a recovery of the reservoir zone elevation, the down wasting of the receiving zone (−17 m, 2007–2014), and a return to quiescent velocities. The short active phase, the abrupt change in the velocities, and the high level of the proglacial stream indicate a hydrological switch (Alaska type) trigger. The 2002–2006 and 1984–1990 surges of Horcones Inferior were synchronous with the surges of nearby Grande del Nevado Glacier. These events occurred after periods of positive mass balance, so we hypothesize a climate driver.

Exposure of Rural Communities to Climate Variability and Change: Case Studies from Argentina, Colombia and Canada

This paper presents results from studies of exposure to climate change and extreme events in the Mendoza River Basin in western Argentina, the Chinchina River basin in the Colombian Andes, and the Oldman River basin and Swift Current Creek watershed in the Canadian Prairies. These case studies are a major component of an international research project: “Vulnerability and Adaptation to Climate Extremes in the Americas” (VACEA). This project is very much interdisciplinary; with social and natural science providing context and direction for research in the other realm of scholarship, producing insights that very likely would not arise from a more narrow disciplinary perspective. A large number of interviews with local actors revealed that agricultural producers and local officials recognize their high degree of exposure and sensitivity to climate variability and extreme weather events, although they generally do not associate this with climate change. Case studies of exposure demonstrate that the perceptions of the local actors are consistent with the nature of the regional hydroclimatic regimes. In all four river basins, climate variability between years and decades masks any regional expression of global climate change. These modes of periodic variability dominate the paleoclimate of past centuries and the recorded hydroclimate of recent decades. The exposure variables examined in this paper, indices of stream flow, snowpack, water excess and deficit, vary in coherence with the characteristic frequencies of large-scale ocean–atmosphere circulation patterns, specifically the ENSO and PDO. Projections of the future states of these variables require the use of climate models that are able to simulate the internal variability of the climate system and the teleconnections between ocean–atmosphere oscillations and regional hydroclimate.