The Snowline and 0°C Isotherm Altitudes During Precipitation Events in the Dry Subtropical Chilean Andes as Seen by Citizen Science, Surface Stations, and ERA5 Reanalysis Data

Understanding the variability of the snowline and the closely related 0°C isotherm during infrequent precipitation events in the dry Andes in Chile is fundamental for precipitation, snow cover, and discharge predictions. For instance, it is known that on the windward side of mountains, the 0°C isotherm can be several hundreds of meters lower than on the free air upwind counterpart, but little is understood about such effects in the Andes due to missing in situ evidence on the precipitation phase. To bridge this gap, 111 photographs of the snowline after precipitation events between 2011 and 2021 were gathered in the frame of a citizen science programme to estimate the snowline altitude. Since photographs of the mountain snowline are in good agreement with Sentinel-2 imagery, they have great potential to validate empirical snowline estimations. Using the snowline altitude from the photos, we evaluated different methods to estimate the snowline and 0°C isotherm altitude during precipitation events based on surface meteorological observations and ERA5 reanalysis data. We found a high correlation between the observed snowline altitude and the extrapolated 0°C isotherm based on constant lapse rates (−5.5 to −6.5°C km−1) applied to air temperature from single, near stations. However, uncertainty increases for distances >10 km. The results also indicate that the linear regression method is a good option to estimate ZSL, but the results strongly depend on the availability of high-elevation station datasets. During half of the precipitation events, the 0°C isotherm lies between ∼1,800 and ∼2,400–2,500 m asl. in winter, and the snowline is on average ∼280 m below this altitude. Our results indicate the presence of a mesoscale lowering of the 0°C isotherm over the windward slopes compared to the free-air upwind value during precipitation events and a possible isothermal layer of near-freezing air temperatures comparable to other mountain ranges. Due to this mesoscale and local behavior, ERA5 data generally overestimate the snow–rain transition in high-elevation areas, especially for relatively intense events. On the other hand, the 0°C isotherm altitude is underestimated if only low-elevation valley stations are considered, highlighting the importance of high-altitude meteorological stations in the network.Fil: Schauwecker, Simone. Centro de Estudios Avanzados En Zonas Áridas; ChileFil: Palma, Gabriel. Centro de Estudios Avanzados En Zonas Áridas; ChileFil: MacDonell, Shelley. University of Canterbury; Nueva Zelanda. Centro de Estudios Avanzados En Zonas Áridas; ChileFil: Ayala, Álvaro. Centro de Estudios Avanzados En Zonas Áridas; ChileFil: Viale, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Air temperature, radiation budget and area changes of Quisoquipina glacier in the Cordillera Vilcanota (Peru)

The Peruvian Andes host about 71% of all tropical glaciers. Although several studies have focused on glaciers of the largest glaciered mountain range (Cordillera Blanca), other regions have received little attention to date. In 2011, a new program has been initiated with the aim of monitoring glaciers in the centre and south of Peru. The monitoring program is managed by the Servicio Nacional de Meteorología e Hidrología del Perú (SENAMHI) and it is a joint project together with the Universidad San Antonio Abad de Cusco (UNSAAC) and the Autoridad Nacional del Agua (ANA). In Southern Peru, the Quisoquipina glacier has been selected due to its representativeness for glaciers in the Cordillera Vilcanota considering area, length and orientation. The Cordillera Vilcanota is the second largest mountain range in Peru with a glaciated area of approximately 279 km2 in 2009. Melt water from glaciers in this region is partly used for hydropower in the dry season and for animal breeding during the entire year. Using Landsat 5 images, we could estimate that the area of Quisoquipina glacier has decreased by approximately 11% from 3.66 km2 in 1990 to 3.26 km2 in 2010. This strong decrease is comparable to observations of other tropical glaciers

Can we use TRMM-PR bright band heights to estimate the snow-rain transition in high mountain regions?

Field and modelling based research indicates that for tropical glaciers, variations in snow cover and the altitude of the snow line via albedo effects are among the most crucial factors to explain the differences in annual glacier mass balance variability. It is therefore essential to identify the height of the phase change during precipitation events and its coupling with glacier mass balance. This knowledge is also fundamental to assess possible future impacts of e.g. changing air temperatures on glacier mass balances at low latitudes. However, the knowledge on heights of phase changes and air temperature during precipitation events is severely limited by the small number of meteorological measurements at high altitudes in the tropics and the Himalaya. Additionally, their one-dimensional type of observation that cannot appropriately account for the variations along the vertical dimension. Remote sensing data are promising tools to fill these data gaps. Before using remote sensing products for studying surface processes, it is crucial to know their accuracies and limitations. Here, we use the the bright band (BB) calulation of the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) as provided in the product 2A23. The bright band is a horizontal layer of stronger radar reflectivity produced by the melting of precipitation at the level where solid precipitation turns into rain. It may be thus a good proxy for the snowline during precipitation events at high mountain regions. To our knowledge, the potential of this product in studies of glacier surface processes has not been further evaluated so far

The freezing level in the tropical Andes, Peru: An indicator for present and future glacier extents: the freezing level in the tropical Andes

Along with air temperatures, the freezing level height (FLH) has risen over the last decades. The mass balance of tropical glaciers in Peru is highly sensitive to a rise in the FLH, mainly due to a decrease in accumulation and increase of energy for ablation caused by reduced albedo. Knowledge of future changes in the FLH is thus crucial to estimating changes in glacier extents. Since in situ data are scarce at altitudes where glaciers exist (above ~4800 m above sea level (asl)), reliable FLH estimates must be derived from multiple data types. Here we assessed the FLHs and their spatiotemporal variability, as well as the related snow/rain transition in the two largest glacier-covered regions in Peru by combining data from two climate reanalysis products, Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar Bright Band data, Micro Rain Radar data, and meteorological ground station measurements. The mean annual FLH lies at 4900 and 5010 m asl, for the Cordillera Blanca and Vilcanota, respectively. During the wet season, the FLH in the Cordillera Vilcanota lies ~150 m higher compared to the Cordillera Blanca, which is in line with the higher glacier terminus elevations. Coupled Model Intercomparison Project version 5 (CMIP5) climate model projections reveal that by the end of the 21st century, the FLH will rise by 230 m (±190 m) for Representative Concentration Pathway (RCP) 2.6 and 850 m (±390 m) for RCP8.5. Even under the most optimistic scenario, glaciers may continue shrinking considerably, assuming a close relation between FLH and glacier extents. Under the most pessimistic scenario, glaciers may only remain at the highest summits above approximately 5800 m asl

Relevance of future snowfall level height in the Peruvian Andes for glacier loss in the 21st century under different emission scenarios

In many regions of Peru, the competition for limited hydrological resources already represents a large risk for conflicts. In this context, and within the circumstances of climate change, there is a great interest in estimating the future loss of Peruvian glaciers. Solid precipitation on glaciers, which affects the shortwave radiation budget via its effects on albedo, in general reduces ablation. For that reason, the height of the upper level of the transition zone between liquid and solid precipitation (snowfall level height) is considered to play a critical role. This snowfall level height is linked to air temperature. The observed and projected warming of the atmosphere is therefore affecting the glaciers amongst others by changing the snowfall level height. Despite the potential significance of these changes for Peruvian glaciers, the relations between snowfall level heights, glacier extents and climate scenarios have been poorly investigated so far. In our study, we first analyse the snowfall level heights over the Peruvian Cordilleras

Snow and ice in the desert: reflections from a decade of connecting cryospheric science with communities in the semiarid Chilean Andes

Citizen science and related engagement programmes have proliferated in recent years throughout the sciences but have been reasonably limited in the cryospheric sciences. In the semiarid Andes we at the Centro de Estudios Avanzados en Zonas Áridas have developed a range of initiatives together with the wider community and stakeholder institutions to improve our understanding of the role snow and ice play in headwater catchments. In this paper we reflect on ongoing engagement with communities living and working in and near study sites of cryospheric science in northern Chile as a strategy that can both strengthen the research being done and empower local communities

Future runoff from glacierized catchments in the Central Andes could substantially decrease

In Peru, about 50% of the energy is produced from hydropower plants. An important amount of this energy is produced with water from glaciated catchments. In these catchments river streamflow is furthermore needed for other socio-economic activities such as agriculture. However, the amount and seasonality of water from glacial melt is expected to undergo strong changes. As glaciers are projected to further decline with continued warming, runoff will become more and more sensitive to possible changes in precipitation patterns. Moreover, as stated by a recent study (Neukom et al., 2015), wet season precipitation sums in the Central Andes could decrease up to 19-33 % by the end of the 21st century compared to present-day conditions. Here, we investigate future runoff availability for selected glacierized catchments in the Peruvian Andes. In a first step, we apply a simplified energy balance and runoff model (ITGG-2.0-R) for current conditions

Understanding climate-driven processes for data-scarce mountain glaciers : insights from reanalysis data and global climate models, as well as in-situ and remote sensing sources

Most glaciers in the world have been shrinking since the middle of the 19th century. Vanishing glaciers in the tropical Andes and the Himalayas may have severe local and regional impacts on water availability and natural hazards. The observed changes in high mountains, together with the often strong emotional and spiritual connection of local cultures to glaciers, have given rise to worries about adaptation to climate change and related glacier shrinkage. Despite the increasing concern about the future of glaciers in countries like India and Peru, there are still important knowledge gaps in understanding the complex interplay between glaciers and climate. It is still not completely unraveled how glaciers react to changes in climate variables like humidity, cloud cover, air temperature and precipitation. One important reason for this incomplete understanding is the data scarcity at high elevations in many parts of the world. Although national weather services, as well as numerous research institutions and groups have made large efforts to monitor the climate at high altitudes, long time series are still sparse and the station density is often low at elevations where glaciers exist. Since remote sensing and reanalysis data have the potential to fill these gaps, it is important to know their potential and limitations. The general aim of this work was to study changes in key climate variables and impacts on glacier mass and energy balance based on simple but robust approaches and multiple data sources, such as in-situ, remote sensing and reanalysis data and global climate models. A first focus of this thesis lies on the energy balance of debris-covered glaciers. Supraglacial debris cover is an important surface characteristic altering glacier surface energy and mass fluxes. Thick debris has an insulating effect and leads to reduced ablation compared to a debris-free surface, while thin debris increases ablation due to the low albedo. Since debris-covered glaciers are widespread in the Indian Himalaya, it is crucial to know the debris extent and thickness. Here, an approach to estimate debris thickness was developed based on several assumptions on the meteorological conditions and debris properties. Several approaches to estimate wind velocity as well as shortwave and longwave radiation were developed and presented and the applicability of reanalysis data was tested. The resulting debris thickness map is related to large uncertainties – especially for thick debris. However, there is great potential to identify parts of the glacier with thin debris, which is important information for hydrological models and future glacier scenarios. To understand glacier shrinkage in the Cordillera Blanca in Peru, past trends of the key climate variables air temperature, freezing level and precipitation were studied using in-situ and reanalysis data. A method to homogenize meteorological station data was developed in order to identify significant trends. Reanalysis data of the upper troposphere indicate that the increase in precipitation recorded in the beginning of the 90s was related to stronger winds from the east, bringing more humidity from the Atlantic and Amazon basin to the mountains. The findings from meteorological data showed that the temperature increase not linear, but characterized by years of strong increases or jumps, followed by periods of slower warming or even stagnant temperatures. It was found that glaciers are retreating in this region, despite of a slowdown in warming and an increase in precipitation in the last 30 years. Based on a simple approach, it was shown that the observed precipitation increase was likely not large enough to balance the increased ablation due to rising temperatures. The estimated glacier reaction times indicate that large glaciers may still be reacting to a strong warming that happened some decades ago. Glaciers are in an imbalance with the present-day climate and especially small and low-elevated glaciers will disappear in a few years or decades. These findings also highlight that the snowfall level is a crucial parameter in glacier energy and mass balance of tropical glaciers. The altitude of the snow/rain transition is decisive since it determines not only accumulation, but also ablation via the snowline, albedo and net shortwave radiation - the primary energy source for ablation. Based on several data sources (including novel data sets from a Micro Rain Radar, TRMM Precipitation Radar bright band and meteorological in- situ stations) and a simple approach bringing together knowledge from studies on different tropical glaciers, this study shows that the wet season snowfall level is approximately at the terminus elevation of the largest glaciers and that a close relation between glacier extents and freezing level exists. The wet season freezing level was used as indicator to estimate future glacier extents by the end of this century. The results impressively show that glaciers may shrink strongly even under optimistic emission scenarios. Under the most pessimistic scenario, only few patches of snow, ice and firn may remain at the summit of the largest mountains in Peru. The approaches presented here provide new insights into climate-driven processes on high-mountain glaciers and their interplay with key climate variables. This thesis summarizes the main result and gives an overview of different applications of in-situ as well as reanalysis and remote sensing data, showing possibilities and limitations when such data are used to study climate-driven glacier surface processes in data-poor regions

Gletscherschmelze unter Schuttbedeckung: Verbreitung, Prozesse und Messmethoden

Schuttbedeckte Gletscher kommen in praktisch allen vergletscherten Gebirgen der Erde vor. Der Schutt wird von verschiedenen Herkunftsorten um, über und unter dem Gletscher auf die Gletscherzunge transportiert – zahlreiche Prozesse greifen dafür ineinander. Einmal dort abgelagert beeinflusst der Schutt die Schmelzrate des darunterliegenden Gletschereises wesentlich. Eine wichtige Funktion fällt dabei der Mächtigkeit und der Zusammensetzung des Schuttmantels zu, welche bestimmen, ob das darunterliegende Eis gegenüber der schuttfreien Gletscherfläche schneller schmilzt, oder ob das Eis durch die darüberliegende Schuttschicht isoliert und dadurch thermisch geschützt wird. Der Schutt verändert aber auch die Oberflächeneigenschaften dieser Gletscher grundlegend, wobei vor allem kleine Schmelzwasserseen und Eisklippen, aber auch veränderte Fliesseigenschaften einen grossen Einfluss auf die Massenverluste der Gletscherzunge haben können. Wissenschaftler suchen unter anderem nach Fernerkundungsmethoden, die Dicke der Geröllschicht auf den Gletscherzungen flächendeckend besser abzuschätzen. Messungen von schuttbedeckten Gletschern werden sowohl direkt auf deren Oberfläche als auch aus der Luft oder dem All vorgenommen, wobei das Hauptaugenmerk vor allem auf den meteorologischen Bedingungen, den Schutteigenschaften und deren räumlichen und zeitlichen Variabilität liegt. Glacier melt under debris: Distribution, processes and measuring methods: Debris-covered glaciers occur in basically all glacierized mountain ranges on Earth. The debris is transported onto the glacier tongue by a variety of processes, originating from different zones around, above and below the glacier. Once deposited there, the debris significantly affects the melting rate of the underlying ice. An important function here is the thickness and the composition of the debris mantle, which determine whether the underlying ice melts faster compared to the debris-free glacier surface or whether the ice is isolated by the overlying debris layer and thus thermally protected. The debris also fundamentally changes the surface properties of these glaciers, with small meltwater ponds and ice cliffs in particular, but also changing flow properties, which can have a major impact on the mass losses of the glacier tongue. Among other things, scientists are looking for remote sensing methods to better estimate the thickness of the debris layer on glacier tongues. Measurements of debris-covered glaciers are carried out both directly on their surface as well as from the air or from space, with the main focus on the meteorological conditions, the properties of the debris and their spatial and temporal variabilit