EVAPORATION FROM A RIPARIAN SYSTEM IN A SEMIARID ENVIRONMENT

Measurements of micrometeorological variables were made for a complete annual cycle using an automatic weather station and two energy budget -Bowen ratio systems at a field site adjacent to the Santa Cruz River in southern Arizona. These data were used to provide the basis of an e stimate of the evaporation from a one-mile long losing reach of a ripa rian corridor in this semi-arid environment. A remotely sensed map of vegetation cover was used to stratify the corridor into five categorie s of surface cover. The total evaporation was calculated as the area-w eighted average of the measured evaporation for sampled areas of the t wo most common covers, and appropriate estimates of evaporation for th e less common covers. Measurements showed a substantial, seasonally de pendent evaporation from the taller, deep-rooted riparian cover in the study reach, while the short, sparse vegetation provided little evapo ration. In terms of the volume of water evaporated from the study reac h, the evaporation from irrigated agriculture accounts for almost half of the total loss, while the majority of the remaining evaporation is from the taller riparian vegetation covers, with about one-quarter of the total loss estimated as coming from obligatory phreatophytes, pri marily cottonwood. (C) 1998 John Wiley & Sons, Ltd.