Submitted to: Experiment Station Bulletins
Publication Type: Other
Publication Acceptance Date: 12/1/2010
Publication Date: 12/30/2010
Citation: Marek, T.H., Porter, D.P., Gowda, P., Howell, T.A., Moorhead, J.E. 2010. Assessment of Texas evapotranspiration (ET) networks. AREC 201011-12, p. 367 Interpretive Summary: Evapotranspiration (ET) is defined as a measure of the total water demand through evaporation from soil and transpiration of plants to the atmosphere. Evapotranspiration is said to equal potential ET (maximum ET for a given set of atmospheric conditions) when there is ample water available (i.e. non-stressed conditions). Reference ET is the preferred term to potential ET and involves the use of a reference crop, which is either well-watered grass or alfalfa. It is the preferred term for use in estimating the potential ET of a crop. Reference ET can be accurately computed from meteorological data recorded from weather stations that are properly sited and instrumented with calibrated sensors. In this study, we evaluated the current status of ET network and other source data in Texas for potential and beneficial water conservation use with irrigation decision support systems. Results indicated that the existing ET networks and other data sources are not sufficient for managing all the irrigated agriculture areas in Texas. Furthermore, documentation associated with available data from many of the networks and sources are generally insufficient to make appropriate adjustments of data parameters for accurate ET computations and subsequently irrigation management decisions.
Technical Abstract: This study was conducted to evaluate the current status of evapotranspiration (ET) data and networks in Texas for potential and beneficial conservation use with irrigation decision support systems. Objectives of this study included (1) identification of existing networks and the meteorological parameter data that each network acquires; (2) evaluation of meteorological parameter sensitivity on reference ET computation; (3) analysis of sensor calibration and degradation data; and (4) comparison of reference ET data from agriculturally based networks and non-ET data sources. Based on the analysis, we found that (1) numerous data sources existed within the state, however, they fell short of the number anticipated; (2) the number and scope of previously established agriculturally based ET networks has declined with several more currently in jeopardy of ceasing operation; (3) a surprising number of "miner" sites that poll and compile meteorological data within Texas are located outside the region for a variety of reasons and applications; and (4) there is little to no adherence to any sensor or data standardization with a common quality assurance/quality control protocol among the various networks or data sources. Use of such data without qualification can directly lead to error prone computations, analysis, and incorrect results. The sensitivity analysis produced significant insight as to the required degree of sensor and parameter accuracy. Furthermore, inference as to the maintenance requirement of sensors on a routine basis became vitally clear from the computational analysis. While the sensor degradation analysis was limited to only one commercially available database, the results indicate a significant finding in that even new sensors often are faulty (or out of calibration) and can produce erroneous measurements and thus should be validated immediately after field installation. Comparison of parameter data from differing network sources for potential use in reference (and agricultural) crop ET computations indicate that much manipulation is generally required, and documentation was generally insufficient to make the appropriate parameter adjustments. School-Net type networks were found to be of no value in representative agricultural based ET computations or applications.