Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

El Niño and glacier melt in the tropical Andes

22.10.2004


Glacier regression in the tropical Andes has accelerated considerably over the past 30 years. This change is cause for great concern, insofar as many regions of the Andes depend on the Cordillera’s glaciers for their water supply (2).



In 1991 scientists from the IRD research unit Great Ice (UR032) set up an observation network, jointly with their Bolivian, Peruvian and Ecuadorian partners. This system takes in a dozen glaciers along the Andes between the Equator and longitude 16°S (Bolivia). In contrast to the Alpine glaciers which undergo a long accumulation period in winter and a short ablation season in summer, the glaciers of the tropical Andes experience an ablation regime in their lower part throughout the year, with a maximum during the Southern summer (October to April) in Bolivia and Peru. That is the season when the strongest insolation coincides with the maximum rainfall. The glaciers, which react strongly to oscillations in these two parameters and are therefore highly sensitive indicators of climate changes. The scientists focused on two representative glaciers from among those scattered over the Cordillera: Antizana (5760-4800 m) in Ecuador and Chacaltaya (5375-5125 m) in the North of Bolivia.

The glacier mass balance, which is an estimate of the difference between the accumulation of snow and ice and their ablation by melting and sublimation, appears to be strongly controlled by the ENSO (El Niño-Southern Oscillation). During the latter’s warm phases (El Niño), the balances are always negative. In the course of a year, the glaciers lose the equivalent of a sheet of water of 600 to 1200 mm. In the cooler and more humid La Niña phase, however, the glaciers return to equilibrium and sometimes show a small increase which temporarily checks their decline.


It is vitally important to identify the physical processes responsible for the surface melting and sublimation occurring on the glacier. The research team therefore determined the energy-balance on Zongo Glacier (3) (16°S) in Bolivia, close to that of Chacaltaya, and in Antizana (0°28S) in Ecuador (4). They thus found the amount of energy received and absorbed by the glacier resulting from solar radiation and turbulent flow. Such quantities are calculated from meteorological data (including relative humidity, temperatures, wind direction and velocity) collected at the glacier surface over complete years. The energy-balance investigations show that glacier melt here is governed mainly by the net radiation, which represents the fraction of radiant energy the glacier absorbs. This emphasizes the determinant role of the glacial surface’s reflective power, the albedo (5). Melting is at its height in Bolivia during the Southern summer (October to April) and in Ecuador in the months close to the equinoxes (April-May and September), from the moment the energy input and atmospheric humidity are at their maximum.

During the El Niño periods rainfall declines by 10-30%. The rain-snow line on the glaciers climbs by 200-300 m consequent on atmospheric warming by 1-3°C. The albedo is thus kept low and melting accelerates. However, whereas in Bolivia the melt acceleration process stems from a decrease in rainfall, essentially in the form of snowfalls (therefore at high albedo), in Ecuador they are rather linked to increase in atmospheric temperature which transforms snowfalls into rain on the lower half of the glacier. La Niña periods, however, offer a cooler atmosphere and frequent and abundant precipitation, giving the glacier surface a continuous protective blanket of snow doted with a high albedo.

Analysis of mass balance determinations made over several decades at the scale of the central Andes shows that glaciers give a consistent response to the same climatic signal. Hence the periods of intense melting coincide with El Niño episodes in the Pacific, with a lag-time of 2 to 3 months. Moreover, the increase in the glacier regression rate since the end of the 1970s appears to be in synchrony with the Pacific shift of 1976, the date after which the El Niño event became more frequent and more intense. The average annual deficit of Chacaltaya Glacier in Bolivia thus increased from 0.6 m of water between 1963 and 1983 to more than 1.2 m between 1983 and 2003. At this rate it would disappear before 2015.

On the century scale, the oscillatory pattern of ENSO is superimposed on the tendency for regression which has been affecting the central Andean glaciers from at least 1880 (end of the Little Ice Age). In a process of climatic forcing, the warm phases would therefore accelerate deglaciation by reinforcing this tendency, attributed to global warming, which for between 20 and 30 years has been at work in the Cordillera at the faster rate of 0.3°C per decade.

The Great Ice scientists are currently working to model the response of these glaciers to possible climatic scenarios predicted for the XXIst Century. This they are doing by means of general circulation models elaborated for the tropical Andes. In this way they should offer populations whose living depends on the glaciers’ water resource a means of effective prediction of the amount of water that will be available in the future.

Isabelle Chaffaut / Marie Guillaume – IRD
Translation : Nicholas Flay

(1) This research is being conducted in partnership with the Bolivian Institute of Hydraulics and Hydrology (IHH) and the Ecuador National Institute of Meteorology and Hydrology (INAMHI).

(2) Ramirez, E., Francou, B., Ribstein, P., Descloîtres, M., Guérin, R., Mendoza, J., Gallaire, R., Pouyaud, B., & Jordan, E.: Small glaciers disappearing in the tropical Andes. A case study in Bolivia : Glaciar Chacaltaya (16°S). J. Glaciol., 2001, 47, 157 : 187-194

(3) Zongo Glacier, which is larger than Chacaltaya, reacts to climatic oscillations in the Pacific in a similar fashion.

(4) Favier, V., Wagnon, P. & Ribstein, P.: Glaciers of the outer tropics: a different behaviour but a common response to climatic forcing. Geophys. Res. Let., 2004, in press.
Wagnon, P., Ribstein, P., Francou, B. & Sicart, J.E.: Anomalous heat and mass budget of Zongo Glacier, Bolivia, during the 1997-98 El Niño year. J. Glaciol., 2001, 47, 156 : 21-28.

(5) In the tropics and at high altitude, solar radiation is intense and the albedo plays a dominant role. The higher this reflective power is, the greater the quantity of energy returned towards the atmosphere. This leads to a decrease in melting rate.

Marie Guillaume | alfa
Further information:
http://www.ird.fr

More articles from Earth Sciences:

nachricht Two satellites see newborn Tropical Storm Jimena consolidating
28.08.2015 | NASA/Goddard Space Flight Center

nachricht NASA's GPM satellite analyzes Tropical Storm Erika's rainfall
28.08.2015 | NASA/Goddard Space Flight Center

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

A Barcode For Shredding Junk RNA

28.08.2015 | Life Sciences

OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

28.08.2015 | Physics and Astronomy

Two satellites see newborn Tropical Storm Jimena consolidating

28.08.2015 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>