Daily analysis

Daily actual evapotranspiration maps were produced for the Valmasino catchment on the two dates.

Figure 7 shows a transect of the aETd obtained from late winter map. The highest values correspond to evergreen forest located in the lower part, below 1000 m, of the Valmasino watershed. An average decrease in evapotranspiration values can also be observed from lower to higher elevations.

From the seasonal maps obtained, mean values were computed for each vegetation land cover class. These results are presented in Table 2 together with percentages of watershed surface occupied by each vegetation type. A general increment of aETd values for all vegetation cover is showed passing from late winter to late spring season. During winter time, all the vegetated land covers present similar values of daily evapotranspiration. Changes in evaporative rate in these two seasons reflect the phenological and photosyntetical seasonal patterns. In May, herbaceous covers show aETd values higher than forested areas and, within forests, evergreen presents values greater than deciduous.

Figure 7. Daily actual évapotranspiration (aETj) as derived from remotely-sensed data is compared with traditional methods at the Bagni di Masino station
Table 2. Average évapotranspiration aETd values of the land cover classes and correspondent

Land cover class

Daily actual evapotranspiration (mm/day)

Area (%)

30* May 1996

Q7'h March ¬°997

Herbaceous rangeland

9.7

4.2

0.3

Herbaceous tundra

9.9

4.0

4.2

Deciduous forest

6.1

4.1

9.0

Evergreen forest

7.1

4.5

11.3

Mixed forest with rock and debris

6.3

3.4

7.2

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