Energy balance calculations from five years' meteorological records at Vernagtferner, Oetztal Alps

During the months May to September, global radiation, longwave radiation, air temperature, relative humidity, precipitation, wind speed and direction are continuously recorded at the Pegelstation Vernagtbach (2640 m a. s. 1.). Based on this material, monthly means of global radiation, air temperature and monthly sums of precipitation for the years 1978 to 1982 are discussed with respect to their influence on shortwave radiation balance and sensible heat flux of Vernagtferner. As the Albedo, which is derived from daily photographs of the glacier increases while global radiation decreases during summer, shortwave radiation balance usually rises from May to August; the lowest value was observed in June 1982 with 48 Wm-2, the highest one in August 1980 with 96 W/m2. The Variation of sensible heat flux follows the change of air temperatures, as wind speed does not vary much during summer. Meltwater production as calculated from the energy balance, lies between 5 % and 30 % below the total measured runoff

Two decades of runoff measurements (1974 to 1993) at the pegelstation Vernagtbach/Oetztal Alps

This report summarizes the runoff data collected at the "Pegelstation Vernagtbach" in the Oetztal Alps, Tyrol. The drainage basin controlled by the Station Covers 11.44 km2, of which 81 % is glacierized by Vernagtferner and hasan altitudinal ränge from 2635 m a.s.l. to 3635 m a.s.l., with 3115 m a.s.l. as the mean altitude. Runoff records, which start in 1974, are given as monthly, daily and hourly mean values. In addition, the mean diurnal Variation is presented for each month. The records show the typical features of the glacier runoff regime, with high discharge during fair weather periods in summer, and low discharge during bad weather and throughout the winter and spring; thus, on average, about 90 % of annual runoff is recorded between June and September. The climatic pattern of the two decades and the resulting mass balances of Vernagtferner tend towards increasing runoff amounts, in particular since the middle of the 1980s. 1991 was the year with highest runoff (0.806 nr/s yearly average), August 1992 delivered the highest monthly mean (4.048 m/s), on July 19,1987 an average daily runoff of 6.123 m3/s was recorded, and 10.68 m3/s was the highest hourly average on August 22, 1993. The rise in absolute amounts was accompanied by increasing diurnal variations, which, on average, were less than 1 m3/s in August 1974, but almost 5 m / s in the same month of 1992

Comparison of mass balances for Vernagtferner, Oetzal Alps, as obtained from direct measurements and distributed modeling

The direct comparison of modeled glacier mass-balance distribution with field measurements could be problematic, as the methodology of determination and the processes considered at the point or catchment scale could differ strongly. Moreover, direct measurements cover only small parts of a glacier, and model performance is thus difficult to assess outside these regions. Remaining opportunities for model validation include comparison of snowlines, as derived from remote-sensing data, and maps of the mass-balance distribution, as interpreted by observers with local knowledge. This study compares such hand-drawn maps of the Vernagtferner (Oetzal Alps) mass balance with the modeled pattern as obtained from a distributed energy-/mass-balance model of intermediate complexity. The model is driven by measured daily values of temperature, global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums. Compared with the direct measurements, the calculated mean mass balance and equilibrium-line altitude agreed very well in both balance years, although the spatial pattern of the mass-balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations. However, compared with the remaining snow as visible on a satellite image from 1999, the modeled snowline pattern for a larger sample of glaciers is in very good agreement