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0.11 0.09 N M E v 0.07 0.05 ,. 20 c� : 10 a E t 0 d -10 D.C. Goodrich et at /Agricultural and Forest Meteorology 105 (2000) 281 -309 19 20 21 22 23 24 25 26 October 1996 Fig. 2. San Pedro River discharge from the USGS gage at Charleston, AZ (top); air temperature measured at mesquite tower, Lewis Springs, AZ (bottom). between riparian ET and streamflows in the USPB is indirectly illustrated in Fig. 2. In the top portion of this figure, discharge from the US Geological Survey (USGS) stream gage at Charleston (Fig. 1) is plot- ted from 19 to 26 October 1996. The bottom part of the figure illustrates air temperature from the Lewis Springs site (Fig. 1) south of the Charleston Gage. Prior to the first hard freeze, occurring late on 21 Oc- tober 1996 the streamflow exhibits a distinct diurnal pattern that is closely correlated with air temperature and presumably riparian ET. After the freeze, the di- urnal pattern immediately dissipates and the discharge increases indicating the hard freeze put a halt to ripar- ian ET. Similar diurnal patterns in shallow well wa- ter levels in the floodplain alluvium during the ripar- ian growing season illustrate the close coupling be- tween groundwater, surface water, riparian vegetation, and atmospheric processes in the USPB (MacNish et al., 1998). Current estimates of riparian ET water use are substantial in this basin. Based on calibrated groundwater model estimates (Vionnet and Maddock, 1992; Corell et al., 1996), riparian ET accounts for 285 roughly 40% of the total basin groundwater discharge. Therefore, better understanding and methods to quan- tify riparian ET are essential to the management and preservation of this system. The most intensive set of coordinated measurements took place in the perennial river reach surrounding the Lewis Springs site. Different hydrologic regimes were included in the study by making a subset of measure- ments at the intermittent Boquillas Ranch site and the ephemeral Escapule wash site (Fig. 1). Measurements were made prior to and throughout the 1997 ripar- ian growing season. While some measurements were made on a near - continuous basis (e.g. meteorology, stream stage), five intensive synoptic measurement sets were made over periods ranging in length from 48 to 120 h. The synoptic measurement periods spanned a period from March to October during the follow- ing days of the year (DOY — Julian Day Of Year) 111 -112, 158 -160, 191 -194, 223 -228, and 285 -289. This period spans the pre - green -up and growing sea- son to allow for characterization of the seasonal vari- ations in ET, and surface- water - groundwater interac- tions. During these synoptic measurement periods, a variety of coordinated remotely sensed and ground measurements were made. 3.2. Remotely sensed measurements An essential component in estimating riparian ET is the determination of the area for various vege- tation types or classes within the riparian corridor. The primary data sources utilized for the riparian vegetation classification were: (1) a 12 -band the- matic mapper simulator (TMS) deployed aboard a NASA Jet Propulsion Laboratory aircraft, and (2) high - resolution color infrared (CIR) photography ob- tained from a 9 in. format mapping camera aboard a USDA -ARS aircraft from Weslaco, TX (Moran et al., 1998; Goodrich et al., 2000). The riparian corridor was defined using a combination of USGS one -arc second digital elevation model (DEM) data and CIR photography. A detailed discussion of the procedures and imagery employed to obtain the vegetation classi- fication and the respective class areas is presented in Appendix A. Single - channel thermal data from an Inframetrics sensor (inclusion of company or product names is for information purposes only and does not indicate