Réf. Collins 2008 - A

Référence bibliographique complète
COLLINS D. N. Climatic warming, glacier recession and runoff from Alpine basins after the Little Ice Age maximum. Annals of Glaciology, 2008, Vol. 48, p. 119-124.

Abstract: Records of discharge of rivers draining Alpine basins with between 0 and ~70% ice cover, in the upper Aare and Rhône catchments, Switzerland, for the period 1894–2006 have been examined together with climatic data for 1866–2006, with a view to assessing the effects on runoff from glacierized basins of climatic warming coupled with glacier recession following the Little Ice Age maximum. Annual runoff from ice-free basins reflects precipitation variations, rising from minima between 1880 and 1910 to maxima between the late 1960s and early 1980s. The more highly glacierized the basin, the more runoff mimicked mean May–September air temperature during two periods of warming. Runoff increased gradually from the 1900s, rapidly in the 1940s, before decreasing to the late 1970s. Rising runoff levels during the second warming period failed to exceed those attained during the first, despite higher summer temperatures. Although temperatures continued to rise, discharge from glacierized basins declined after reaching maxima in the late 1980s to early 1990s. In the first warming period, rising specific melt rates augmented by increasing precipitation opposed the impact of declining glacier area on runoff. Although melt continued to increase in the second period, enhanced melting (even in the exceptionally warm summer of 2003) appears to have been insufficient to offset reducing glacier surface area exposed to melt, low or reducing levels of precipitation, and increasing evaporation. Thus runoff from glacierized basins peaked in the late 1940s to early 1950s.

Mots-clés
Climate change, Alpine basins, glaciers, discharge, Swiss Alps.

Organismes / Contact
School of Environment & Life Sciences, University of Salford, Salford Crescent, Manchester M5 4WT, UK. d.n.collins@salford.ac.uk

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
Temperature, Precipitation Rivers (discharge)    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Alps (Aare and upper Rhône basins) Allenbach, Grande Eau, Lonza, Rhône and Massa basins   ~400-4200 m a.s.l. 1866-2006 (climatic data)
1894-2006 (discharge data)

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
After a decade of summer air temperatures above the longterm average, T 5–9 declined until the 1890s. After the warm summer of 1911, from a minimum in 1912, summer temperatures generally increased until the late 1940s–early 1950s, the first warming cycle, with a maximum of 18.7°C in 1947, before declining until the late 1970s with a minimum of 15.0°C in 1978. A second warming period, from the 1980s to the early 21st century, included the warmest summer (19.9°C in 2003) in the 1866–2006 record, on an underlying gently rising linear trend of ~0.015°C a-1 from the 1880s.

Total annual precipitation between November in one year and October in the next (P 11–10) showed considerable year-to-year fluctuation. After several wet years in the 1860s–70s, precipitation at Sion from the 1880s to 1900s was generally below the long-term average of 571 mm, although 1895/96 was the wettest year in the series (the second wettest at Zermatt). Between the 1900s and 1950s, precipitation varied about a slightly rising trend, but with several exceptionally dry (1920/21, 1924/25) and wet years (1944/45) at Sion. The cool 1970s had both dry and wet years but with no trend through to the warm 1990s–2000s, which included the second wettest year in the record (1989/90) but with several years below average. After the wet years from the mid-1970s to 1981/82, P 11–10 for Zermatt declined, with the majority of annual values below the station average, including 1989/90.
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Mean May–September air temperature (T 5–9) recorded at Sion (Couvent des Capucins), although located at only 549 m a.s.l., has been shown to have high correlation with Q 1–12 from glacierized basins throughout the upper Rhône catchment (Collins, 1989). The station recorded from 1866 to 1977. Collins (1989, 2006) estimated subsequent annual values of T 5–9 for Sion from observations at Grächen (1617 m a.s.l.) and Saas Almagell (1669 m a.s.l.). Homogenized temperature data are now produced for Sion (Aéroport, 482 m a.s.l.) since 1978 (Bader and Bantle, 2004; Begert et al., 2005). Correlation between T 5–9 data used by Collins (2006) and respective values taken from the homogeneous series is high; the homogeneous series is used in this paper.

Long precipitation series are available from Sion for 1865–1977 and Zermatt for 1893–1922 at 1609 m and for 1926–2006 at 1632 m a.s.l. Homogenized monthly precipitation data from Meteo-Schweiz for Sion Aéroport now provide an extended series at one location. Correlation between homogenized data for Sion and actual data from Zermatt is weak, reflecting the natural spatial variability in year-to-year total annual precipitation in mountainous terrain.

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
Annual total runoff from the (near-) ice-free basins of Allenbach and Grande Eau generally reflected the temporal variation of precipitation, rising to maxima in the late 1970s–early 1980s and late 1960s respectively. P 11–10 at Sion was reasonably correlated with Q 1–12 of both Grande Eau and Allenbach (r > 0.6). Year-to-year fluctuations of runoff in the two basins were broadly parallel until the 1990s. Mean decadal flow in the Allenbach and Grande Eau declined by 11% and 16% respectively from 1977–86 to 1997–2006.

Runoff in the Massa, which drains the most highly icecovered of the glacierized basins (~66% glacierized), mimicked the cyclical pattern of variation in T 5–9 at Sion. The correlation between T 5–9 and Q 1–12, whilst generally strong, was greater the shorter the time period considered. High discharge in 1928 resulted from a warm spring with precipitation slightly above average. Rising temperatures, together with increasing precipitation, led to runoff generally increasing over subsequent years, with a maximum in 1947. Declining summer air temperatures next reduced runoff to a minimum in 1978. During the second warming cycle (1980s-2006), temperatures exceeded those experienced in the 1940s. However, mean discharge in the warmer 1990s–2000s failed to exceed that of the 1940s–50s.

The Rhône drains the second most highly glacierized basin of the study. Correlation of T 5–9 at Sion with runoff in the Rhône was not as strong as for flow in the Massa, whereas correlation of P 11–10 with runoff was more positive for the Rhône, for respective periods. Runoff in the two rivers was strongly correlated. Discharge in the Rhône also increased from the cooler 1960s–70s to the warmer 1980s–2000s but by only 12%, whereas quinquennial average annual runoff in the Massa increased by almost 50% between 1974–78 and 2001–05, accompanying a rise in mean T 5–9 from 16.1°C to 18.1°C. In fact, runoff at Gletsch increased from 1977–86 to 1987–96, before decreasing in 1997–2006.

The pattern of temporal variation of discharge in the Lonza (~38% glacierized) was to an extent intermediate between that in the Allenbach (0%) and the Rhône (~54%). Correlation with T 5–9 at Sion was weaker than for the more highly glacierized basins, and with P 11–10 weaker than for the (near-)ice-free basins. Correlation of runoff in the Lonza with that in the Rhône was, however, greater than with that in rivers draining the (near-) ice-free basins. Runoff in the Lonza increased between 1977–86 and 1987–96, before decreasing in 1997–2006.
Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Alpine river discharges are correlated with summer temperature (for glacierized basins) and annual precipitation.
The study basins are located in the upper Aare and upper Rhône basins in Switzerland. Percentage glacierization of basin area was taken from the contemporary annual Hydrologisches Jahrbuch der Schweiz (e.g. BAFU, 2006). The Allenbach basin is ice-free. The Grande Eau basin is almost ice-free. Total glacier-covered areas of about 32 and 22 km2 in the Lonza and Rhône basins declined by about 10% and 7.5% respectively between 1977 and 2002. Percentage glacierization of the Massa basin (recalculated to take into account catchment area change) reflects a loss of total icecovered area of about 8 km2 (6%) from 136.6 km2 between 1934 and 2002, of which about three-quarters had disappeared by 1957.

The Rhône was gauged in a natural cross-section at Gletsch for 1894-1903 and 1920-1928 periods, before use of a flume structure from 1956. The Lonza is gauged from 1956. Following dam construction, from 1965 the Massa was gauged at Blatten-bei-Naters, upstream of the former station at Massaboden, reducing basin area by 3.47%. Runoff is unlikely to have been proportionally reduced.

Total annual runoff was taken as the total for the calendar year (Q 1–12). Mean May–September air temperature (T 5–9) was used to indicate heat-energy availability for melting. Total annual precipitation between November in one year and October in the next (P 11–10) reflects build-up of winter snowpack and summer rainfall which affect total annual discharge between January and December (Q 1–12) in the second year.

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Paramètre de l'aléa
Sensibilité des paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 

(4) - Remarques générales
 

(5) - Syntèses et préconisations
 

Références citées :

Bader, S. and H. Bantle. 2004. Das Schweizer Klima im Trend. Temperatur- und Niederschlagsentwicklung 1864–2001. Veröff. MeteoSchweiz 68.

Begert, M., T. Schlegel and W. Kirchhofer. 2005. Homogeneous temperature and precipitation series of Switzerland from 1864 to 2000. Int. J. Climatol., 25 (1), 65–80. [Fiche Biblio]

Bundesamt für Umwelt (BAFU). 2006. Hydrologisches Jahrbuch der Schweiz 2004 . Bern, Schweizerische Eidgenossenschaft. Bundesamt für Umwelt.

Collins, D.N. 1989. Hydrometeorological conditions, mass balance and runoff from alpine glaciers. In Oerlemans, J., ed. Glacier fluctuations and climatic change . Dordrecht, etc., Kluwer Academic Publishers, 235–260.

Collins, D.N. 2006. Climatic variation and runoff in mountain basins with differing proportions of glacier cover. Nord. Hydrol., 37 (4–5), 315–326.