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Observations on glacier extent from Ecuador, Peru and Bolivia give a detailed and unequivocal account of rapid shrinkage of tropical Andean glaciers since the Little Ice Age (LIA). This retreat however, was not continuous but interrupted by several periods of stagnant or even advancing glaciers, most recently around the end of the 20th century. New data from mass balance networks established on over a dozen glaciers allows comparison of the glacier behavior in the inner and outer tropics. It appears that glacier variations are quite coherent throughout the region, despite different sensitivities to climatic forcing such as temperature, precipitation, humidity, etc. In parallel with the glacier retreat, climate in the tropical Andes has changed significantly over the past 50–60 years. Temperature in the Andes has increased by approximately 0.1 °C/decade, with only two of the last 20 years being below the 1961–90 average. Precipitation has slightly increased in the second half of the 20th century in the inner tropics and decreased in the outer tropics. The general pattern of moistening in the inner tropics and drying in the subtropical Andes is dynamically consistent with observed changes in the large-scale circulation, suggesting a strengthening of the tropical atmospheric circulation. Model projections of future climate change in the tropical Andes indicate a continued warming of the tropical troposphere throughout the 21st century, with a temperature increase that is enhanced at higher elevations. By the end of the 21st century, following the SRES A2 emission scenario, the tropical Andes may experience a massive warming on the order of 4.5–5 °C. Predicted changes in precipitation include an increase in precipitation during the wet season and a decrease during the dry season, which would effectively enhance the seasonal hydrological cycle in the tropical Andes.
shows an analysis of near-surface temperature trends based on a compilation of 279 station records between the 1°N and 23°S. These results are based on an update of previous studies by Vuille and Bradley (2000) and Vuille et al. (2003a) through 2006. Individual station records have been assembled into a single time series by using the first difference method and by first gridding the data to avoid any regional bias (Vuille and Bradley, 2000). The results show that near-surface air temperature has significantly increased over the last ~70 years. An ordinary least squares regression analysis indicates a warming of 0.10 °C/ decade and an overall temperature increase of 0.68 °C since 1939. Of the last 20 years only 2 (1996 and 1999) were below the long-term (196190) average. This rate of warming is similar to previous reports of 0.100.11 °C/decade between 1939 and 1998 (Vuille and Bradley, 2000) and 0.15 °C/decade between 1950 and 1994 (Vuille et al., 2003a). On a more regional scale a number of studies provide additional evidence for significant warming over the last decades of the 20th century. In central Peru (9-11°S), Mark (2002) and Mark and Seltzer (2005a), based on 29 low and high-elevation stations, found a temperature increase of 0.35-0.39 °C/decade between 1951 and 1999. Vuille et al. (2000a,b) based on a principal component analysis of station data found a significant warming trend since the mid-1970s in southern Bolivia and northernmost Chile. Toumi et al. (1999) reported significant warming (0.20 °C/decade between 1954 and 1987) at La Quiaca, a highelevation (3462 m) station at the border between Bolivia and Argentina by utilizing station pressure change as an indicator of warming. Quintana-Gomez (1997), based on daily temperature records from
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... It is expected that climate change will continue to affect the mass balance of tropical glaciers in the Andes, leading to its decline and even disappearance (Vuille et al. 2008). Among the most affected glaciers are Chacaltaya (approx. ...
Thesis
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During the last years, Climate Change has proven to have negative effects in the livelihoods of rural communities. It is argue that adaptation to climate change and climate variability is important in order to diminish the dangerousness of their impacts. Some authors, decision makers and practitioners argue that adaptation to climate change needs to be institutionalized in order to achieve its adequate implantation. Furthermore, it is argue that it should be mainstreamed into development policies. However, multi-level processes of institutional change related to adaptation to climate change have not been deeply explored. In general, studies focus on adaptation whether at the local level or national or international level. Hence, there is limited knowledge about the translation of climate change adaptation into practice by actors at different levels of governance. This research analyses the process of institutionalization of adaptation to climate change and the related institutional changes at different levels of resource governance and its relation to vulnerability and adaptive capacity by taking three case studies in Bolivia as an example. The research builds on primary information gathered at fieldwork and secondary information from (non)governmental documents. The analysis was developed by applying two analytical frameworks: climate vulnerability and adaptive capacity framework; and multi-level governance framework. The findings show that the institutionalization of adaptation to climate change in Bolivia is taking its first steps and it is encountering several barriers. One important barrier is the nonprioritization of adaptation by the communities when it comes to municipal planning. Hence, it still corresponds to a reactive regime rather than to an adaptive one. The process of institutionalization is not following a stepwise fashion where all levels of governance are at the same stage of the process. In fact, each level of governance is at a different stage. Moreover, the findings show that there is a tendency for the integration of adaptation to climate change into development rather than for its mainstreaming. The study gives practical recommendations in relation to adaptation to climate change. Among them, it identifies the need to facilitate climate information to community members and grassroots organizations in order for them to make informed decisions and demands. As well, it suggests to decrease the tension between adaptation and development in order to foster planned adaptation.
... El calentamiento acelerado del sistema climático es innegable e influencia los patrones de precipitación, temperatura, escorrentía, radiación y humedad, con considerables efectos sobre la disponibilidad de los recursos hídricos (Furniss et al., 2010;IPCC, 2013IPCC, , 2014IPCC, , 2022. En el caso de la precipitación, los patrones de distribución y cantidad (aumento o disminución de precipitación) no tienen una tendencia definida entre regiones; sin embargo, a nivel global los escenarios sugieren un incremento del 2% en el promedio de lluvias desde los inicios del siglo XX (Dore, 2005), tendencias que han sido validadas para Sudamérica, incluyendo Ecuador (TNC, 2010;Vuille et al., 2008). En cuanto a la temperatura, en Sudamérica se espera un aumento en la temperatura promedio anual de hasta 1,5 °C bajo un escenario optimista RCP 2,6 (Representative Concentration Pathways) y hasta 5,0°C bajo un escenario pesimista RCP 8,5. ...
Article
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En las últimas décadas se ha observado una fuerte infl uencia de las actividades antrópicas sobre micro-cuencas que proveen el servicio ecosistémico hídrico. A eso se suman los posibles impactos del cambio climático relacionados a variaciones extremas en temperatura y precipitación que podrían generar una alta vulnerabilidad dentro de las microcuencas y servicios ecosistémicos primordiales para el desarrollo de las comunidades. El presente estudio analiza cuál podría ser el grado de vulnerabilidad de dos microcuencas de alta montaña de importancia hídrica en la Región Sur de Ecuador. Para el análisis de vulnerabilidad se consideró la exposición, sensibilidad y la capacidad adaptativa. Los resultados muestran que las microcuencas El Carmen CA (cabecera de agua) y Mónica en el Cantón Loja podrían tener una vulnerabilidad moderada a alta bajo escenarios pesimistas (RCP 8,5). En lo concerniente a la capacidad adaptativa, se observó que El Carmen y Mónica poseen niveles de capacidad adaptativa altos. Estos resultados están relacionados a la presencia de estrategias de conservación en dichas microcuencas y muestran la importancia de generar acciones de conservación y restauración a nivel de paisaje, que permitan el mantenimiento y recuperación de ecosistemas que proveen el servicio ecosistémico hídrico, de esta manera también se podría asegurar la calidad y cantidad de agua para las comunidades. Palabras clave: vulnerabilidad al cambio climático, exposición climática, capacidad adaptativa, Andes.
... Some of the slightly higher mass change rates (Willis et al., 2011(Willis et al., , 2012Abel Jaber, 2016;Malz et al., 2018) can be attributed to their different methodology and time frames as well as the assumption of 2 m Shuttle Radar Topography Mission (SRTM) radar penetration (Willis et al., 2011(Willis et al., , 2012, which was best practice at that time, but now proven to be erroneous for the NPI (Dussaillant et al., 2018). This agrees with previous studies (Vuille et al., 2008;Vuille et al., 2018). In the inner tropics (region 01), the rise in temperature is less pronounced. ...
Thesis
Glaciers on Earth along other components of the cryosphere are important for the climate system. However, it is widely known that the vast majority of glaciers are retreating and thinning since the early part of the 20th century. Additionally, future projections have highlighted that at the end of the 21st century, glaciers are going to lose a considerable part of their remaining mass. These glacier changes have several implications for physical, biological and human systems, affecting the water availability for downstream communities and contribute to sea level rise. Unlike other regions, where glaciers are less relevant for the overall hydrology, glaciers in South America constitute a critical resource since minimum flow levels in headwaters of the Andean mountains are usually sustained by ice melt, especially during late summer and droughts, when the contribution from the seasonal snow cover is depleted. In the last decades, the number of studies has increased considerable, however, in the Southern Andes and the surrounding sub-Antarctic islands glaciers still are less studied in comparison with their counterparts in the Northern Hemisphere. The few studies on glacier mass balance in this region suggest a risk of water scarcity for many Andean cities which freshwater supply depends on glacial meltwater. Additionally, glaciers on sub-Antarctic islands have not been completely assessed and their contribution to the sea level rise has been roughly estimated. Hence, the monitoring of glaciers is critical to provide baseline information for regional climate change adaptation policies and facilitate potential hazard assessments. Close and long-range remote sensing techniques offer the potential for repeated measurements of glacier variables (e.g. glacier mass balance, area changes). In the last decades, the number of sensors and methods has increased considerably, allowing time series analysis as well as new and more precise measurements of glacier changes. The main goal of this thesis is to investigate and provide a detailed quantification of glacier elevation and mass changes of the Southern Andes with strong focus on the Central Andes of Chile and South Georgia. Six comprehensive studies were performed to provide a better understanding of the development and current status of glaciers in this region. Overall, the glacier changes were estimated by means of various remote sensing techniques. For the Andes as a whole, the first continent-wide glacier elevation and mass balance was conducted for 85% of the total glacierized area of South America. A detailed estimation of mass changes using the bi-static synthetic aperture radar interferometry (Shuttle Radar Topography Mission -SRTM- and TerraSAR-X add-on for Digital Elevation Measurements -TanDEM-X- DEMs) over the years 2000 to 2011/2015 was computed. A total mass loss rate of 19.43 ± 0.60 Gt a-1 (0.054 ± 0.002 mm a-1 sea level rise contribution) from elevation changes above ground, sea or lake level was calculated, with an extra 3.06 ± 1.24 Gt a-1 derived from subaqueous ice mass loss. The results indicated that about 83% of the total mass loss observed in this study was contributed by the Patagonian icefields (Northern and Southern), which can largely be explained by the dynamic adjustments of large glaciers. For the Central Andes of Chile, four studies were conducted where detailed times series of glacier area, mass and runoff changes were performed on individual glaciers and at a region level (Maipo River basin). Glaciers in the central Andes of Chile are a fundamental natural resources since they provide freshwater for ecosystems and for the densely populated Metropolitan Region of Chile. The first study was conducted in the Maipo River basin to obtain time series of basin-wide glacier mass balance estimates. The estimations were obtained using historical topographic maps, SRTM, TanDEM-X, and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results showed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, with more negative values between 2000 and 2013. A mean basin-wide glacier mass balance of −0.12 ± 0.06 m w.e. a-1 , with a total mass loss of 2.43 ± 0.26 Gt between 1955–2013 was calculated. For this region, a 20% reduction in glacier ice volume since 1955 was observed with associated consequences for the meltwater contribution to the local river system. Individual glacier studies were performed for the Echaurren Norte and El Morado glaciers. Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service. An ensemble of different data sets was used to derive a complete time series of elevation, mass and area changes. For El Morado Glacier, a continuous thinning and retreat since the 20th century was found. Overall, highly negative elevation and mass changes rates were observed from 2010 onwards. This coincides with the severe drought in Chile in this period. Moreover, the evolution of a proglacial lake was traced. If drained, the water volume poses an important risk to down-valley infrastructure. The glacier mass balance for the Central Andes of Chile has been observed to be highly correlated with precipitation (ENSO). All these changes have provoked a glacier volume reduction of one-fifth between 1955 and 2016 and decrease in the glacier runoff contribution in the Maipo basin. The thesis closes with the first island-wide glacier elevation and mass change study for South Georgia glaciers, one of the largest sub-Antarctic islands. There, glaciers changes were inferred by bi-static synthetic aperture radar interferometry between 2000 and 2013. Frontal area changes were mapped between 2003 and 2016 to roughly estimate the subaqueous mass loss. Special focus was given to Szielasko Glacier where repeated GNSS measurements were available from 2012 and 2017. The results showed an average glacier mass balance of −1.04 ± 0.09 m w.e. a-1 and a mass loss rate of 2.28 ± 0.19 Gt a-1 (equivalent to 0.006 ± 0.001 mm a-1 sea level rise) in the period 2000-2013. An extra 0.77 ± 0.04 Gt a-1 was estimated for subaqueous mass loss. The concurrent area change rate of the marine and lake-terminating glaciers amounts to −6.58 ± 0.33 km2 a-1 (2003–2016). Overall, the highest thinning and retreat rates were observed for the large outlet glaciers located at the north-east coast. Neumayer Glacier showed the highest thinning rates with the disintegration of some tributaries. Our comparison between InSAR data and GNSS measurements showed good agreement, demonstrating consistency in the glacier elevation change rates from two different methods. Our glacier elevation and mass changes assessment provides a baseline for further comparison and calibration of model projection in a sparsely investigated region. Future field measurements, long-term climate reanalysis, and glacier system modelling including ice-dynamic changes are required to understand and identify the key forcing factors of the glacier retreat and thinning.
... It has also been speculated that an infrequent occurrence of chemical signatures of dust originating from the Saharan-Sahel region may be present in glaciochemical records within Central Andean ice cores (Thompson et al. 2017;Lindau et al. 2020). Westerly flow over the Andes (Vuille et al. 2008;Thompson et al. 2013). From seasonally clustered back trajectories, westerly-Pacific moisture sources are observed to be the most significant in JJA (Clusters 1,4: 46%), SON (Clusters 3,4: 31%), and MAM (Clusters 3,4: 30%), while only contributing to 2% of the clusters from DJF (Figure 3.3-3.7). ...
Article
The goal of this dissertation is to assess past and present changes in the chemical climate of three high mountain regions: the Himalayas, Peruvian Andes, European Alps. In the first analysis, we report a comprehensive case study of chemical composition from streams, snow samples, and an ice core collected from around Mt. Everest Basecamp in the Khumbu region of Nepal during the late pre-monsoon period. Our findings document the 2019 pre-monsoon season, detailing chemistry from Cyclone Fani, spatial variability in snow and stream chemistry, and addressing potential pollution hazards, including the presence of heightened Pb in local streams and possible chemical signature of human waste. This is the first study to characterize the chemical composition of Khumbu Glacier ice/meltwater and create a detailed framework for pre-monsoon snow/water chemistry for the region. The second study details the correspondence in chemical climate resulting from two regional Central Andean firn cores (Quelccaya ice cap, Peru (5470 m asl) and Nevado Illimani glacier, Bolivia (6350 m asl)) and investigates the environmental proxies associated with Central Andean climate. The results show that the Quelccaya core has well-preserved environmental signals despite meltwater percolation, the two regional ice core records contain comparable signals and similar regional scale climatology, and past records of anthropogenic emissions, dust sources, volcanic emissions, forest fire signatures, evaporite salts, and marine-sourced air masses are evident within the cores. Moreover, annual layer thickness established from ultra-high-resolution chemical measurements on a near-basal ice core from the Quelccaya glacier indicates that Quelccaya ice cores drilled to bedrock may be ~1000 years older or more than previously suggested by depth-age models. Lastly, the third study focuses on a 2100-year record of heavy metals (Pb, As, Cd, Bi, Cu) extracted from a European Alps ice core, which is the first known case in which these elements have been observed in unison and at this resolution for this timespan in the European Alps. Chemical signatures resulting from decomposition analyses indicate a strong relationship between Pb, As, and Cd, a connection between Cu and marine chemistry (Na, K), and Bi retaining a unique signal that exhibits a distinct increase during the pre-industrial revolution between 1710-1850CE. We hypothesize that heavy metal concentrations likely reflect the timing of emerging technological advances related to the industrial revolution and periods of important past societal eras, including expanding mining activities, pandemics, and wars. In the Appendix, we address the importance of data analysis and visualizations in the field of Earth and Climate Sciences.
... For instance, the reconstructed south-central precipitation, the southwestern lake size, and the average scPDSI for the Altiplano also highlight the occurrence of arid conditions during this late 20th-beginning 21th centuries period (Fig. 7). These results are consistent with the rapid retreat of 375 glaciers across the tropical Andes during the second half of the 20th century (Ramírez et al., 2001;Francou et al., 2003;Vuille et al., 2008;Jomelli et al., 2009). On the other hand, this abrupt change towards more arid conditions was also recorded since the 1970s onwards in the Quelccaya ice core (Thompson et al., 2006) synchrony shown by all the other proxies records across the southern tropical Andes (Fig. 7 and Fig. S2), suggesting largescale common atmospheric and ocean forcings over this Andean region. ...
Preprint
Given the short span of instrumental precipitation records in the South American Altiplano, long-term hydroclimatic records are needed to understand the nature of climate variability and to improve the predictability of 25 precipitation, a key natural resource for the socioeconomic development in the Altiplano and adjacent arid lowlands. In this region grows Polylepis tarapacana, a long-lived tree species that is very sensitive to hydroclimatic changes and have been widely used for tree-ring studies in the central and southern Altiplano. However, in the northern sector of the Peruvian and Chilean Altiplano (16º-19º S) still exist a gap of hydroclimatic tree-ring records. Our study provides an overview of the temporal evolution of annual precipitation for the period 1625-2013 CE at the northern South American Altiplano, allowing 30 for the identification of wet or dry periods based on a regional reconstruction composed by three P. tarapacana chronologies. An increase in the occurrence rate of extreme dry events, together with a decreasing trend in the reconstructed precipitation, have been recorded since the 1970s decade in the northern Altiplano within the context of the last ~four centuries. The average precipitation of the last 17-year stands out as the driest in our 389-years reconstruction. We revealed a temporal and spatial synchrony across the Altiplano region of wet conditions during the first half of the 19th century and the 35 drought conditions since mid 1970s recorded by independent tree-ring based hydroclimate reconstructions and several 2 paleoclimatic records based on other proxies available for the tropical Andes. The rainfall reconstruction provides also valuable information about the ENSO influences in the northern Altiplano precipitation. The spectral properties of the rainfall reconstruction showed strong imprints of ENSO variability at decadal, sub-decadal and inter-annual timescale , in particular from the Pacific N3 sector. Overall, the remarkable recent reduction in precipitation in comparison with previous 40 centuries, the increase in extreme dry events and the coupling between precipitation and ENSO variability reported by this work is essential information in the context of the growing demand for water resources in the Altiplano that will contribute to a better understanding of the vulnerability/resilience of the region to the projected evapotranspiration increase for the 21st century associated to global warming.
... Several studies have shown the high (negative) correlation between annual air temperature and glacier mass balance in tropical regions [65]. Notably, the freezing level heights (FLHs), i.e., the elevation where the 0 • C air temperature is found, has been used as a proxy for the TAGs mass balance [15,66,67]. ...
Article
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The fast retreat of the tropical Andean glaciers (TAGs) is considered an important indicator of climate change impact on the tropics, since the TAGs provide resources to highly vulnerable mountain populations. This study aims to reconstruct the glacier coverage of the TAGs, using Landsat time-series images from 1985 to 2020, by digitally processing and classifying satellite images in the Google Earth Engine platform. We used annual reductions of the Normalized Difference Snow Index (NDSI) and spectral bands to capture the pixels with minimum snow cover. We also implemented temporal and spatial filters to have comparable maps at a multitemporal level and reduce noise and temporal inconsistencies. The results of the multitemporal analysis of this study confirm the recent and dramatic recession of the TAGs in the last three decades, in base to physical and statistical significance. The TAGs reduced from 2429.38 km2 to 1409.11 km2 between 1990 and 2020, representing a loss of 42% of the total glacier area. In addition, the time-series analysis showed more significant losses at altitudes below 5000 masl, and differentiated changes by slope, latitude, and longitude. We found a more significant percentage loss of glacier areas in countries with less coverage. The multiannual validation showed accuracy values of 92.81%, 96.32%, 90.32%, 97.56%, and 88.54% for the metrics F1 score, accuracy, kappa, precision, and recall, respectively. The results are an essential contribution to understanding the TAGs and guiding policies to mitigate climate change and the potential negative impact of freshwater shortage on the inhabitants and food production in the Andean region.
... This is worrying since it has been revealed that knowledge about climate change is a critical determinant of the behavior of rural producers, especially in order to achieve adaptation strategies [147,148]. In addition, in the Ecuadorian Andes, there is a lack of thinking in terms of planning in the face of the existing and future scenarios of climate change [149][150][151], considering that the increase in temperatures, the retreat of glaciers, and changes in the frequency and intensity of precipitation and frost have been documented in the Andean highlands over the past thirty years [152][153][154][155][156], which has coincided with greater uncertainty and the exposure to multiple climatic stresses in the northern highlands of Bolivia [157]. This coincides with the results of a changing climate in the study area, where the producers from Q1 to Q5 responded more frequently to the option "Yes a little". ...
Article
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The Sustainable Development Goals (SDG) of 2015 identify poverty, growth, and inequality as three key areas of intervention towards the UN 2030 Agenda for human well-being and sustainability. Herein, the predominant objectives are: (a) To determine the poverty groups by quintiles through the cattle income in households of small milk producers; (b) To characterize rural livelihoods by using capital theory; and (c) To assess the perception of climate change (CC) and the willingness to accept adaptation as well as mitigation measures. The current study was performed in communities that are located in the Ecuadorian Andes, where some 178 surveys were conducted with indigenous Kichwa and mestizo heads of households. From the total net income determined, five groups were organized. The Lorenz curve was applied as a general indicator of the relative inequality, as well as the Gini coefficient (G). On the basis of the theory of capital, the human, social, natural, physical, and financial characteristics were determined, and seven variables were considered to evaluate the perception and willingness to accept mitigation and adaptation actions of the given quintiles. The result of the Gini coefficient was 0.52, which indicates that the poorest 20% of the population only receives 3.40% of the income, while the richest 20% of the quintile obtain about 54% of the total income. It is evident that most producers know little about CC, but that they are willing to receive strengthening programs. Therefore, it is essential to establish strategic guidelines from public policy in order to reduce inequality and to improve the social welfare of producers, with a transversal axis in the strengthening of the capacities on the impact, mitigation, and adaptation to CC, as well as the provision of several tools, such as access to climate information.
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South America is a vast continent characterized by diverse atmospheric phenomena and climate regimes. In this context, seasonal climate predictions are helpful for decision-making in several relevant socioeconomic segments in this territory, such as agriculture and energy generation. Thus, the present work evaluates the performance of ECMWF-SEAS5 in simulating the South American precipitation regimes by applying a non-hierarchical clustering technique. In addition, the study describes the main atmospheric systems that cause precipitation in each cluster and updates a previous work performed in South America in 2010. As a result, ECMWF-SEAS5 simulates (with good correspondence) the eight climate regimes identified in the analysis of precipitation from the Climate Prediction Center (CPC). Moreover, ECMWF-SEAS5 has a satisfactory ability in representing the rainfall regime in low and medium climate predictability regions, such as central and southern South America. ECMWF-SEAS5 has good performance in the climate characterization of South America and it gives us confidence in using its seasonal climate predictions throughout the continent.
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Tropical glaciers are excellent indicators of climate variability due to their fast response to temperature and precipitation variations. At same time, they supply freshwater to downstream populations. In this study, a hydro-glaciological model was adapted to analyze the influence of meteorological forcing on melting and discharge variations at Glacier 12 of Antisana volcano (4,735-5,720 m above sea level (a.s.l.), 1.68 km 2 , 0°29′S; 78°9′W). Energy fluxes and melting were calculated using a distributed surface energy balance model using 20 altitude bands from glacier snout to the summit at 30-min resolution for 684 days between 2011 and 2013. The discharge was computed using linear reservoirs for snow, firn, ice, and moraine zones. Meteorological variables were recorded at 4,750 m.a.s.l. in the ablation area and distributed through the altitudinal range using geometrical corrections, and measured lapse rate. The annual specific mass balance (−0.61 m of water equivalent-m w.e. y −1-) and the ablation gradient (22.76 kg m −2 m −1) agree with the values estimated from direct measurements. Sequential validations allowed the simulated discharge to reproduce hourly and daily discharge variability at the outlet of the catchment. The latter confirmed discharge simulated (0.187 m 3 s −1) overestimates the streamflow measured. Hence it did not reflect the net meltwater production due to possible losses through the complex geology of the site. The lack of seasonality in cloud cover and incident shortwave radiation force the reflected shortwave radiation via albedo to drive melting energy from January to June and October to December. Whereas the wind speed was the most influencing variable during the July-September season. Results provide new insights on the behaviour of glaciers in the inner tropics since cloudiness and precipitation occur throughout the year yielding a constant shortwave attenuation and continuous variation of snow layer thickness.
Article
Oxygen isotopes δ¹⁸O from a 13 m ice core derived from the Antisana volcano ice cap (0° 28′S, 78° 08′W), Ecuador, were analyzed to generate an age model based on isotopic fluctuations. The inferred age model spans c. 3.6 years, from 1993 to mid-1996, and corresponds to 3.6 cycles of isotopic fluctuations driven by seasonal change in precipitation in western Amazonia. A logarithmic transformation (LT) was performed on the ice core density data to remove the compression effect of accumulated snow affecting the temporal fluctuation of the isotopic signal. A wavelet analysis run on the decompressed isotope signal (LT) showed periodicities of 80, 40, and 20 corresponding to 12, 6, and 3 months, respectively. The results were compared against the isotopic record from the Chimborazo ice core data to validate its temporal match with a hydrological year. The LT isotopic signal showed a significant correlation with the Chimborazo isotopic data (r = 0.69 and p-value<0.001). The methodology applied in this study allowed the reconstruction of 3.6 cycles (3.6 years), showing that age models can be derived from ice cores using oxygen isotope annual fluctuations in tropical glaciers.
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Measurements of mass balance were performed every month on Zongo Glacier. Bolivia. Simultaneously, water-discharge, temperature and precipitation data were obtained. The first year of the survey, 1991–92. was marked by an ENSO (El Niño-Southern Oscillation) event with high temperature and low precipitation, whilst the following year, 1992–93, was normal. Results point to the early and late wet season (October-December and March–May: as playing a critical role in the determination of the annual mass balance. The wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance. Both glaciological and hydrological methods for the determination of the mass balance provide similar results. Our study confirms dial ENSO events have a major influence on the rapid glacier retreat currently affecting this part of the Andes.
Article
With a total of 723 km2 of glaciers (1970) the Cordillera Blanca includes the largest glacier-covered area in the tropics. The climate is characterized by relatively large daily and small seasonal temperature variations as well as by a distinct succession between a dry (May–September) and a wet season (October–April). Since the early 1970s an ablation stake network has been installed on the tongues of the glaciers Uruashraju and Yanamarey. The determination of the equilibrium-line altitude at each end of a wet season was possible, showing a fair correlation with temperature, but not with the precipitation records of the nearby climatological station Querococha. Mean ablation rates at the lowest parts of the glacier tongues are markedly higher during the wet season than during the dry season. Reasons are presumably to be found in the seasonal variation of cloudiness and air moisture rates. Terminus variations of four glaciers in the Cordillera Blanca have been monitored since the early seventies, earlier positions are reconstructed back to 1948 by vertical air photographs. For the glaciers Uruashraju and Yanamarey the terminus positions of 1939 are known from an early map. The general retreat of glaciers in the Cordillera Blanca during the last five decades correlates with the global attitude of glaciers and especially with the attitude of glaciers in other tropical areas. Decreased recession rates with minor advances (1974–79 and 1985–86) are accompanied by lower annual temperatures and preceded and accompanied by years with relatively high annual precipitation sums.
Article
For Yanamarey Glacier in Cordillera Blanca, Peru, mostly situated between about 5000 and 4600 m, maps of the surface topography at a scale of 1: 5000 obtained by terrestrial triangulation for 1973, 1982 and 1988 and by aerial photogrammetry for 1948 and 1962 are compared with the glacier boundaries from a 1939 map and an undated maximum extent inferred from moraine morphology. The glacier length decreased from the maximum, 2800 m to 1600 m in 1948. and to 1250 m in 1988, with an accompanying decrease in area from 17 × 105 to 10 × 105 and thence to 8 × 105 m2. The shrinkage of ice volume was 35 × 106 m3 from the maximum to 1948. and 29 × 106 m3 from 1948 to 1988. compared to a total remaining ice volume of about 25 × 106 m3 in 1988. This quantitative assessment of mass-loss rates creates the observational basis for sensitivity studies of the climatic forcing.
Article
During the June-August 1976 Quelccaya ice cap expedition, global, SW↓, and net long-wave radiation, LW↑↓, were measured through several complete day-night cycles, and for a wide range of cloudiness conditions. Field work further included albedo measurements along representative transects across the ice cap and lysimeter-type estimates of ablation. Automatic stations recording wind, temperature and sunshine duration were also installed. Daily totals of SW↓ and LW↑↓ representative of completely clear and overcast days are derived. On this basis, empirical relationships allow the computation of monthly totals of radiation fluxes for an entire year from records of sunshine duration and temperature expected from the automatic stations. The larger part of the plateau is situated above 5400 m and has an albedo mostly in excess of 80%. Sub-freezing temperatures essentially limit ablation to the energetically expensive sublimation. For clear sky, daily totals of SW↓and LW↑↓ are of the order of 312 and 53 W m–2, respectively. With the albedo found, net short-wave radiation SW↑↓ becomes of the same general magnitude as LW↑↓, and the energy left for ablation is near to nil. Cloudiness would reduce both SW↑↓ and LW↑↓, thus largely compensating the effect on the residual net radiation, SWLW↑↓. This is consistent with ablation measurements. Over the larger area of the ice plateau, ablation may be close to zero in a first approximation; some ablation, including melting, takes place near the lower-lying rim of the ice cap, and calving off steep cliffs seems to provide a major mechanism for the disposal of the ice mass.
Article
In recent years there has been a notable increase in the number of tree-ring chronologies for the temperate and cold regions of the Americas. In comparison, few advances have been reported for the American tropics and subtropics, where the absence of seasonality appears to be the main reason for the lack of well-defined growth bands in most species. Distinct, annually formed tree-rings have recently been reported for subtropical montane trees on the eastern slope of the Andes (22-28 degrees S). Six absolute-dated chronologies from Juglans australis and Cedrela lilloi at the upper treeline (between 1700 and 2000 m) in the montane forest of north-western Argentina were selected to explore the potential of these records to infer decade- to century-scale climatic variations in the subtropics. These tree-rings capture a significant percentage of the variances in regional temperature and precipitation records and appear to be suitable to reconstruct decade-long changes in large-scale circulation over the South American subtropics. In particular, tree-growth at xeric sites has been strongly influenced by precipitation changes, which in turn respond to alternating patterns of zonal versus meridional flows over subtropical South America. The upper treeline records indicate that the increase in precipitation during the past three decades, caused by an enhanced transport of humid air masses from the Brazilian-Bolivian lowland tropics to the semiarid subtropics, has been unprecedented for the past 200 years. Although this precipitation increase may reflect natural variability in the subtropics, it is also consistent with 2 x CO2 climatic simulations from five general circulation models. There is a general agreement among model results about a noticeable increase in precipitation in north-western Argentina due to an intensification of the water transport across subtropical South America in response to a southward displacement of the continental low and an increasing warming at these latitudes. A larger network of tree-ring chronologies will aid efforts to understand long-term climatic interactions between tropical and subtropical regions in South America, and shed light on the pole of natural versus anthropogenic forcings on regional climatic changes. (C) 1998 Royal Meteorological Society.