Evapotranspiration at Two Mountain Sites During the Vegetation Period

Hourly values of evapotranspiration (ET) for the months July to September 1976 and 1977 were calculated from energy balance measurements at two test sites near the village of Obergurgl in the Austrian Alps. One test site was situated at 1,960 m a.s.l. on a cultivated meadow near the timberline, the other test site at 2,580 m a.s.l. was covered with alpine sedges and grasses. Examples of the daily variations and daily sums of the energy fluxes are presented for clear and cloudy days. The mean daily courses of ET at the two test sites are shown for every month of the measurement periods; differences in ET between the two test sites are related to the decrease of transpirating leaf areas with altitude. Monthly sums of ET are presented in relation to net radiation and precipitation; on the average ET was about 30% lower at the higher elevated site. High correlations were found between the daily sums of net radiation and of ET at both sites. This relation can be used for calculating ET from radiation measurements.