A canopy model (RM-CWU) for determining transpiration of subalpine forests. II. Consumptive water use in two watersheds

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Abstract
A canopy transpiration model, RM-CWU, was used for estimating consumptive water use (CWU) of subalpine forest stands in the Rocky Mountains. Annual CWU was calculated for nine subunits in two watersheds on the Fraser Experimental Forest near Fraser, CO. Calculated CWU of the forested portions of the subunits ranged from 305 to 460 mm • year−1. After combining these rates on an area-weighted basis with evapotranspiration estimates of the nonforested areas of each subunit, annual subunit CWU rates varied from 159 to 388 mm • year−1. Annual CWU for the Lexen Creek watershed was 352 mm • year−1; for the East St. Louis Creek watershed CWU was 264 mm • year−1. Annual CWU calculated for each watershed with RM-CWU was compared with completely independent estimates of evapotranspiration (ET) determined as the difference between precipitation input and watershed runoff. Using two different estimates of precipitation input, two ET estimates were obtained for each watershed. For both watersheds, CWU calculated with RM-CWU was within several percent of the ET estimates expected to be the most accurate. This suggests that CWU estimates from a physiologically based canopy transpiration model may be used to determine water vapor loss from watersheds in the Rocky Mountains.