Réf. Zemp & al. 2007 - A

Référence bibliographique complète
ZEMP M., HOELZLE M., HAEBERLI W. Distributed modelling of the regional climatic equilibrium line altitude of glaciers in the European Alps. Global and Planetary Change, 2007, Vol. 56, p. 83-100.

Abstract: In this study, a simple approach for modelling the glacier distribution at high spatial resolution over entire mountain ranges is introduced using a minimum of input data. An empirical relationship between precipitation and temperature at the steady-state equilibrium line altitude (ELA0) is derived from direct glaciological mass balance measurements. Using geographical information systems (GIS) and a digital elevation model, this relationship is then applied over a spatial domain, to a so-called distributed modelling of the regional climatic ELA0 (rcELA0) and the climatic accumulation area (cAA) of 1971–1990 over the entire European Alps. A sensitivity study shows that a change in rcELA0 of ±100 m is caused by a temperature change of ±1°C or a precipitation decrease of 20% and increase of 27%, respectively. The modelled cAA of 1971–1990 agrees well with glacier outlines from the 1973 Swiss Glacier Inventory. Assuming a warming of 0.6°C between 1850 and 1971–1990 leads to a mean rcELA0 rise of 75 m and a corresponding cAA reduction of 26%. A further rise in temperature of 3°C accompanied by an increase in precipitation of 10% leads to a further mean rise of the rcELA0 of about 340 m and reduces the cAA of 1971–1990 by 74%.

Mots-clés
Glacier, climate at equilibrium line altitude, climate change, geographical information systems.

Organismes / Contact
Glaciology and Geomorphodynamics Group, Department of Geography, University of Zurich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland. mzemp@geo.unizh.ch

(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
  Glaciers    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Europe Alps        

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
Modélisations
The model run for the reference period 1971–1990 show that over the entire Alps, the cAA covers an area of 3059 km2. As the cAA is simply the terrain above the rcELA0, it does not distinguish between glacier surface and ice-free rock walls. In a first order approach this can be taken into account by applying a slope-dependent glacier fraction to the modelled cAA. The corrected cAA equals 1950 km2 and corresponds to a steady-state Accumulation Area Ratio (AAR0) of 0.67 of the measured total Alpine glacier area in the 1970s, which was 2909 km2 (Zemp et al., in press). The modelled cAA corresponds well overall to the real accumulation areas of Alpine glaciers and there are minor quantities of cAA cells in regions with no glacierisation. A general overestimation of the accumulation areas on SE–SW slopes and underestimation on NE–NW slopes can be found.

A temperature change of ±1°C leads to an average rcELA0 deviation of +137/-125 m, ranging from +112 m (Aosta) to +190 m (Isar) and from -44 m (Vorderrhein) to -201 m (Var), respectively. A precipitation change of ±25% leads to an average rcELA0 deviation of -114/+157 m, with a range similar to the 1°C temperature deviation. MRT-0.6 results in Alpine an average rcELA0-decrease of 75 m, ranging from 24 m to 131 m, and by 65 m within the outlines of the 1973 Swiss Glacier Inventory. The total cAA of the MRT-0.6 run amounts to 4157 km2. MRT+3/P+10 leads to an average rcELA0 rise of 336 m and the disappearance of glaciers in eight out of 28 basins. The corresponding total cAA over the entire Alps shrinks to 812 km2. When the slope-dependent glacier fraction is applied, the cAA of the MRT-0.6 and the MRT+3/P+10 amounts to 2650 km2 and 504 km2, respectively. This corresponds to a cAA deacrease of 26% between 1850 and 1971–1990, and a 1971–1990 cAA decrease of 74%.

The sensitivity model runs show that a temperature change of ±1°C would be compensated by a precipitation increase/decrease of 25%. The relative precipitation change corresponds to a mean absolute change over the greater Alpine region of about 300 mm.
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Equilibrium line altitude and climatic accumulation area are driven by temperature and precipitation changes.
The approach presented in this study is based on the concept of Haeberli (1983) and Shumsky (1964). An empirical relationship between 6-month summer temperature and annual precipitation at the steady-state equilibrium line altitude (ELA0) is derived from direct glaciological mass balance measurements from 14 Alpine glaciers over the 1971–1990 period. Using geographical information systems (GIS) techniques and a digital elevation model (DEM: SRTM3), this relationship is applied for the first time to a distributed modelling of the regional climatic ELA0 (rcELA0) and the climatic accumulation area (cAA) over the entire Alps at a spatial resolution of 3 arc sec (approx. 100 m).

In addition to the model run for the reference period 1971–1990, six more model runs were carried out to study the sensitivity of the ELA0 to changes in temperature and precipitation. Temperature and/or precipitation are altered by a uniform deviation over the entire investigation area. MRT+1 and MRT-1 (temperature +/- 1°C) as well as MRP+25 and MRP-25 (precipitation +/- 25%) are sensitivity studies with deviations only in temperature or precipitation. MRT-0.6 represents a summer temperature cooling of 0.6°C, as assumed by Maisch et al. (2000) for the year 1850. MRT+3/P+10 applies a warming of the summer temperature of 3°C and a concurrent rise in precipitation by 10%. Reference and sensitivity model runs are analysed for individual glacier regions, within the hydrological basins, as derived from the HYDRO1k DEM, and within the 1973 outlines of the Swiss Glacier Inventory (Kääb et al., 2002; Paul et al., 2002) for glaciers larger than 1 km2.

The 14 glaciers used for the empirical relationship are: Gietro, Grosser Aletsch, Rhone, Gries, Plattalva, Silvretta and Limmern (Switzerland), Fontana Bianca and Careser (Italy), Kesselwand, Vernagt, Hintereis, Wurten and Sonnblick (Austria). The ELA0 is calculated for each glacier from the relation between the specific net balance and the ELA, as published in the Glacier Mass Balance Bulletin series (e.g. IUGG(CCS)/UNEP/UNESCO/WMO, 2005).

Precipitation values at the glacier ELA0 were obtained from the Alpine precipitation climatology (1971–1990) published by Frei and Schär (1998) and Schwarb et al. (2001). Based on a comprehensive database with observations from 5831 conventional rain gauges and 259 totalisators (i.e. cumulative precipitation gauges), this gridded data set provides mean monthly precipitation (1971–1990), as well as monthly precipitation–elevation gradients on a spatial resolution of 1.25 arc min (approx. 2 km). The precipitation at the ELA0 is calculated as the mean of all precipitation grid cells covering the glacier accumulation area.

Temperature from 12 Alpine high altitude weather stations was used, with continuous data series between 1971 and 1990. The 12 stations are all located above 2000 m a.s.l., with one exception. Monthly lapse rates are empirically derived from temperature and elevation values of the 12 stations. With these empirically derived lapse rates, seasonal temperatures are altitude-adjusted to 2000 m a.s.l. Using the inverse distance weighted (Watson and Philip, 1985) interpolation method, temperatures are interpolated over the entire Alps. At glacier locations the empirical lapse rates are used again to extrapolate temperatures at 2000m a.s.l. to the ELA0. The same principle is applied to produce an Alpine-wide data set of temperature on terrain, with a resolution of 3 arc sec (approx. 100 m), by extrapolating the temperature field at 2000 m a.s.l. with the seasonal lapse rate to the altitude of a DEM.

Temperature lapse rate and precipitation–elevation gradient were introduced to derive temperature and precipitation at the altitude of instantaneous glacierisation (AIG). The climatic accumulation area (cAA) corresponds to the regions where the altitude of the terrain is above the AIG. The AIG, rcELA0 and cAA are modelled in space using the annual precipitation data and the corresponding annual precipitation–elevation gradients from Frei and Schär (1998) and Schwarb et al. (2001) and 6-month summer lapse rate (0.67°C per 100 m) and 6-month summer temperature on terrain as input raster data sets. The summer temperature data set is extrapolated with the summer lapse rate from the altitude-adjusted temperature field at 2000 m a.s.l. to the altitude of the DEM.

(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
It is shown that the altitude of the terrain is the decisive factor determining the spatial distribution of the rcELA0, and hence also of the cAA, superimposed by the precipitation field and the temperature field at 2000 m a.s.l. The empirical relationship between precipitation and temperature is able to explain about 50% of the variance in precipitation at the glacier ELA0 by the variance in temperature at that location. Hence, the uncertainties in the prediction of precipitation based on a given temperature and the ELA0 at a single location are rather large. Nevertheless, it represents a promising tool for the estimation of precipitation in high altitude terrain based on a large number of ELA0 values. The empirical relationship is used as a boundary condition for the distributed modelling of the rcELA0. The mean absolute difference between modelled rcELA0 and measured ELA0 amounts to about 70 m. The uncertainties of the rcELA0 are restricted to its location, and affect the cAA only in flat terrain. Under the assumption that local, topographic effects and components of the energy balance not included in the model do not change, the distributed modelling approach presented here is an adequate tool for studies of glacier sensitivity to changes in temperature and/or precipitation.

To enhance the statistical basis and to extend the range of validity of the empirical relationship, the authors recommend the determination of monthly, seasonal or at least annual precipitation and temperature at the ELA0 of all glaciers with mass balance measurements. These two parameters together with the calculation of the ELA values should become a standard component of mass balance measurement series.

The presented approach is an excellent complement to distributed mass balance models. As the distributed rcELA0-model requires only a minimum amount of input data to compute the rcELA0 over the entire Alps, distributed mass balance models can then be used to account for further important components of the energy balance (e.g., solar radiation, albedo, turbulent fluxes, mass balance–altitude feedback) and local, topographic effects (e.g., shading, avalanches, snow drift) within individual catchments. In conclusion, distributed modelling of the rcELA0 can potentially contribute to the current efforts to include glacier altitude-area distribution of past, present and future glacier states in regional climate models.

(5) - Syntèses et préconisations
 

Références citées :

Frei, C., Schär, C., 1998. A precipitation climatology of the Alps from high-resolution rain-gauge observations. International Journal of Climatology 18, 873–900.

Haeberli, W., 1983. Permafrost–glacier Relationships in the Swiss Alps Today and in the Past. Proceedings of the Fourth International Conference on Permafrost, Fairbanks AK. National Academy of Sciences, Washington, D.C., pp. 415–420.

IUGG(CCS)/UNEP/UNESCO/WMO, 2005. In: Haeberli,W., Noetzli, J., Zemp, M., Baumann, S., Frauenfelder, R., Hoelzle, M. (Eds.), Glacier Mass Balance Bulletin No. 8 (2002–2003). World Glacier Monitoring Service, Zurich, 100 pp.

Kääb, A., Paul, F., Maisch, M., Hoelzle, M., Haeberli, W., 2002. The new remote-sensing-derived Swiss Glacier Inventory: II. First results. Annals of Glaciology 34, 362–366.

Maisch, M., Wipf, A., Denneler, B., Battaglia, J., Benz, C., 2000. Die Gletscher der Schweizer Alpen. Gletscherhochstand 1850, Aktuelle Vergletscherung, Gletscherschwund Szenarien, Schlussbericht NFP31, 2nd edition. VdF Hochschulverlag, Zurich, 373 pp.

Paul, F., Kääb, A., Maisch, M., Kellenberger, T.W., Haeberli, W., 2002. The new remote-sensing-derived Swiss Glacier Inventory: I. methods. Annals of Glaciology 34, 355–361.

Schwarb, M., Daly, C., Frei, C., Schär, C., 2001. Mean annual and seasonal precipitation throughout the European Alps 1971–1990. Hydrological Atlas of Switzerland. Plates 2.6, 2.7.

Shumsky, P.A., 1964. Principles of structural glaciology. Translated from the Russian by D. Kraus. Dover Publications, Inc., NewYork, 497 pp.

Watson, D.F., Philip, G.M., 1985. A refinement of inverse distance weighted interpolation. Geo-Processing 2, 315–327.

Zemp, M., Paul, F., Hoelzle, M., Haeberli, W., in press. Glacier fluctuations in the European Alps 1850–2000: an overview and spatio-temporal analysis of available data. In: Orlove, B., Wiegandt, E., Luckmann, B. (Eds.), The darkening peaks: Glacial retreat in scientific and social context. University of California Press.