Tropical glaciers in the central Andes cover about 1920 square kilometers in Bolivia (20%), Peru (71%), Ecuador (4%), and Colombia-Venezuela (4%). They play a significant role in freshwater availability in highly populated regions and are key indicators of recent climate changes in poorly documented mountainous regions [Rabatel et al., 2013].
To study them, the French Institut de Recherche pour le Développement (IRD) partnered with local universities and research institutions, founding glaciological programs in Bolivia in 1991 and in Peru and Ecuador in 1994. This grew into a permanent monitoring program, which was incorporated into the global glacier-monitoring network GLACIOCLIM (Glaciers, a Climate Observatory) in 2002. Two of the glaciers that are being monitored—Zongo in Bolivia and Antisana 15 in Ecuador—are now the longest-monitored glaciers in the tropics and are considered benchmark glaciers by the World Glacier Monitoring Service.
The IRD funded the international GREAT ICE (Glacier and Water Resources in the Tropical Andes: Indicators of Changes in the Environment) program in 2011 to strengthen glaciological studies in the tropical Andes; promote collaborative projects between Andean institutions in glaciology, climatology, and hydrology; and develop education and student training programs with local universities.
The GREAT ICE Program
The initiative in Bolivia in 1991 has grown into a network of permanent glacier monitoring with sites in four nations (Figure 1). It includes institutions in France (Laboratoire d’Étude des Transferts en Hydrologie et Environnement, Laboratoire de Glaciologie Geophysique de l’Environnement, University of Grenoble, Maison des Sciences de l’Eau, and Laboratoire de Géographie Physique), Bolivia (Universidad Mayor de San Andrés), Ecuador (Escuela Politécnica Nacional and Instituto Nacional de Meteorología e Hidrología), Peru (Unidad de Glaciología y Recursos Hídricos de la Agencia Nacional de Agua, Servicio Nacional de Meteorología e Hidrología, and Instituto Geofísico del Perú), and Colombia (Instituto de Hidrología, Meteorología y Estudios Ambientales and University of Colombia).
Three main research areas are addressed:
- evolution of the ice masses from the Little Ice Age (13th–19th centuries) to the present
- analysis of glacier ablation and accumulation processes and their relationships with the local to large-scale climate
- impacts of glacier changes on water resources
Research questions include whether the glacier retreat observed in recent decades is unprecedented since the Little Ice Age and how it is related to changes in precipitation and temperature.
Permanent glacier-monitoring networks have been functioning in the central Andes since 1991 in collaboration with local partners (Figure 1). The observation system includes glaciological, hydrological, and meteorological measurements.
Remote sensing studies have used aerial photographs and satellite images to reconstruct the evolution of the surface area, volume, and length of the glaciers since the mid-20th century. Moraines were used to reconstruct glacier fluctuations since the Little Ice Age maximum in the second half of the 17th century. Analysis of ice cores from summits in Ecuador, Peru, and Bolivia revealed information about climate variations on a multidecadal time scale over the last millennium. A comprehensive overview of the GREAT ICE investigations can be found in Rabatel et al. .
Glaciers in Retreat
Like most mountain glaciers worldwide, glaciers in the tropical Andes have been rapidly retreating since the late 1970s. The rate of current retreat appears to be unprecedented since the Little Ice Age maximum [Rabatel et al., 2013]. The magnitude of mass loss seems to be related to the size and elevation of the glacier. Glaciers with a maximum altitude above 5400 meters above sea level (i.e., glaciers that still have a permanent accumulation zone) have typically lost the equivalent in water of 0.6 meters in thickness every year over the last 3.5 decades, whereas glaciers with a maximum altitude lower than 5400 meters have shrunk at an average rate of 1.2 meters water equivalent per year, i.e., at twice the rate of the higher glaciers. Although sporadic positive annual mass balances have been observed on some glaciers, the average mass balance has been mostly negative over the past 50 years.
GREAT ICE has extensively studied the link between glaciers and climate. In the outer tropics of Bolivia and Peru, which are characterized by marked seasonality in cloud cover and precipitation (Figure 2), process-based energy balance studies investigated the atmospheric forcing that controls seasonal and interannual variations in the glacier mass balance [e.g., Sicart et al., 2011]. In the inner tropics of Ecuador and Colombia, studies focused on the relationship between mass balance and climate variability linked to El Niño–Southern Oscillation, which exerts a greater influence there than it does in the outer tropics [Francou et al., 2004].
Solar radiation is the main source of energy, but seasonal changes in melting energy are mainly driven by long-wave radiation—infrared radiation emitted by clouds and moisture in the atmosphere. This radiation is closely linked to clouds and humidity, which are the main seasonal variables of low-latitude climates. Long-wave radiation plays a key role in the energy balance of tropical glaciers. During the melt season, light snowfalls are frequent, and the glacier surface continuously alternates between ice and thin layers of snow that rapidly melt, so that the melt rate strongly depends on the frequent changes in surface albedo.
Tropical glaciers are characterized by large vertical mass balance gradients due to the frequent changes in snow cover throughout the long ablation season. Ablation and accumulation processes are closely related, and the mass balance strongly depends on the timing and length of the wet season, which arrives during the summer months, interrupting the period of highest melt rates caused by solar radiation [Sicart et al., 2011]. GREAT ICE is currently studying the properties of the wet season in terms of precipitation frequency, intensity, and phase.
Glaciers: A Key Water Resource, Under Threat
The supply of water from glacierized mountain chains is critical for agricultural and domestic water consumption as well as for hydropower generation. Glacier runoff will initially increase as the climate warms and glaciers melt at a faster rate, probably resulting in a deceptive increase in water to downstream reaches. However, this increase will then be followed by a sobering reduction in runoff as the glaciers dwindle, affecting water resource availability and reducing the glacier’s capacity to act as a buffer, adding water to the stream flow during periods of low seasonal precipitation.
GREAT ICE has studied the hydrology of glaciers in several regions, including the Peruvian Rio Santa basin, which drains the Cordillera Blanca, the most glacierized tropical mountain range in the world. There, glaciers shrunk by 36% to 528 square kilometers between 1930 and 2003 and contribute up to 20% of annual Rio Santa runoff. In the dry season, around two thirds of runoff comes from glaciers [Condom et al., 2012].
In Bolivia, Soruco et al.  studied the supply of glacier water to the city of La Paz between 1963 and 2006 and showed that glaciers contributed roughly 15% of the water resources at an annual scale—14% in the wet season and 27% in the dry season. In the future, assuming complete disappearance of glaciers and no change in precipitation, they calculated that runoff should diminish by about 12% at an annual scale, 9% during the wet season and 24% during the dry season. This demonstrates the important buffer effects of glacier melt in seasonal changes of runoff.
Glacier melt contribution to runoff is also significant in Ecuador, reaching 35% during the dry season in populated areas around Cayambe, Antisana, Cotopaxi, and Chimborazo mountains [Nolivos et al., 2015].
Training the Next Generation of Glacial Hydrologists
The project has a strong commitment to education and student training, in particular through funding and supervising South American students. The IRD has funded roughly 10 Ph.D. positions in French universities through GREAT ICE programs, which include the opportunity to spend several months in France and to attend international scientific conferences.
These programs connect the students with national and international collaborators, allowing them to broaden their experience and build a professional network. The students also receive chances to disseminate their work via presentations to scientific and nonscientific audiences, popular science publications, and interviews with media and by participating in the making of documentary films.
Next Steps: Biodiversity and Water Management
In the second phase of the GREAT ICE program planned for 2016, a new theme will be proposed: the impacts of glacier changes on terrestrial and aquatic biodiversity. Although plants may be able to colonize new terrain opened up by the glaciers’ retreat, we hypothesize this upward migration to be much slower than glacier retreat itself, at least for a number of key organisms. We expect that this lag will negatively affect the biodiversity and functioning of mountain ecosystems.
Moreover, reduction in glacial meltwater contribution to river flow may potentially affect the specialized aquatic fauna in glacier-fed rivers. The decrease in water availability should also reduce the high Andean wetlands and associated biodiversity and vegetation biomass.
Further efforts in glacier-hydrological modeling are crucial to inform policy makers about how to manage water resources in regions whose glaciers are rapidly shrinking. So far, most studies have been limited to small drainage basins, but we now urgently need to investigate the effect of glacier shrinkage on water resources and availability for human use on the scale of mountain ranges. Hydrologists will need to collaborate closely with climatologists, especially in tropical mountains where the impact of climate change is still uncertain.
The Laboratoire Mixte International program GREAT ICE is supported by the Institut de Recherche pour le Développement (IRD). The glaciological monitoring network is sponsored by the French SO/SOERE GLACIOCLIM (Service d’Observation/Système d’Observation et d’Expérimentation pour la Recherche en Environnement) and Labex [email protected] (Investissements d’Avenir ANR10 LABX56). The co–principal investigators of the GREAT ICE project are Alvaro Soruco (Universidad Mayor de San Andrés, La Paz, Bolivia), Bolivar Caceres and Luis Maisincho (Instituto Nacional de Meteorología e Hidrología, Quito, Ecuador), Wilson Suarez (Servicio Nacional de Meteorología e Hidrología, Lima, Peru), and Jorge Luis Ceballos (Instituto de Hidrología, Meteorología y Estudios Ambientales, Bogota, Colombia). We thank Benjamin Lehmann for providing the photograph of the Huayna Potosí massif.