|Scott, R. - UNIV. OF ARIZ.|
|Qi, J. - MICH. STATE UNIV.|
|Goff, B. - CONSULTANT|
|Williams, D.G. - UNIV. OF ARIZ.|
|Schaeffer, S. - UNIV. OF ARIZ.|
|Snyder, K. - UNIV. OF ARIZ.|
|Mac Nish, R. - UNIV. OF ARIZ.|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2000
Publication Date: N/A
Interpretive Summary: For many of the human settlements in the Southwest, groundwater from regional aquifers has become the largest single source of fresh water for human communities. This reliance on groundwater has led to a large effort to further our understanding of the water balance of these large regional groundwater systems. In the basin and range country of the Southwest the main natural inlet and outlet of the underlying groundwater systems are mountain front recharge and riparian zone recharge/discharge areas. The Upper San Pedro River Basin in southeastern Arizona and northern Sonora, Mexico is an ideal area in which to investigate these poorly understood processes of regional aquifer water balance. A critical component of this water balance is amount of water used by the riparian system. A combination of ground measurements and those from aircraft sensors were used to develop a method to estimate evaporation and transpiration from the San Pedro riparian system. This method was checked using a water balance over a 6 mile reach of the riparian system for 90 days and very good results were obtained.
Technical Abstract: Riparian evapotranspiration (ET) can often be a significant factor in the basin water balance yet is very difficult to estimate. Improved methods to estimate large-area riparian ET was a primary objective of the SALSA Program. Interdisciplinary experiments in 1997 in the San Pedro Basin in SE Arizona were carried out to address this objective. The riparian system consists primarily of mesquite, sacaton grass, and cottonwood/willows (C/W). Micrometeorological techniques were used to estimate ET from the mesquite and grasses. C/W transpiration was determined using sap flux measurements over several periods of the growing season. Simultaneous remote sensing measurements were used to spatially extrapolate tree measurements over the riparian corridor. Scaled, C/W stand level sap flux estimates were utilized to calibrate a Penman-Monteith model to enable temporal extrapolation between measurement periods. To validate the model a a90-day pre-monsoon water balance over a 10 km river reach was carried out. All components of the water balance were independently estimated. The closure of the water balance was roughly 5%. The ET models were then used to provide riparian ET estimates over the entire corridor for the growing season. These estimates were approximately 40% less (20) than those from the most recent groundwater models.