Location: Sustainable Water Management ResearchTitle: Comparison of RZWQM2 simulated evapotranspiration with Eddy Covariance estimates
Submitted to: Abstract of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/2018
Publication Date: 10/15/2018
Citation: Anapalli, S.S., Reddy, K.N., Ahuja, L.R. 2018. Comparison of RZWQM2 simulated evapotranspiration with Eddy Covariance estimates. Abstract of Agronomy Meetings. ..
Technical Abstract: Evapotranspiration (ET) is a resultant of the dynamic interactions of various physical, chemical, and biological processes in the soil-water-atmosphere and state and stages of crop growth. For that reason, accurate quantification of ET remains a challenge for irrigation water management in agriculture. Agricultural system simulation models that realistically simulate the ET processes are potential tools for the integration, synthesis, and extrapolation of location-specific research findings across soils and climates. In this context, the Agricultural Model Inter-Comparison and Improvement Project reported (unpublished data) multi-fold variation in simulated ET among agricultural system models developed around the world. These findings point towards the need for further evaluating those ET simulations against precisely measured experimental data, such as in eddy covariance (EC) and energy balance (EB) systems. The objective of this study was to evaluate the accuracy of Root Zone Water Quality Model (RZWQM) simulated daily ET - in studies in which no ET information was used in model-calibrations - against those measured in corn by EB in 2016 and by EC in 2017, and in soybean by both EB and EC in 2016. An extended approach, based on the Shuttleworth and Wallace (SW) method was used to estimate potential crop ET (E and T separately) demand in RZWQM2. The Nimah and Hanks approach was used for crop water uptake, and Richard’s Equation for soil water redistribution modeling. Across corn and soybean crops in 2016 and 2017, simulated seasonal ET deviated from EC and EB estimates from -11 to 6%. And RMSE of daily ET simulations ranged between 1 and 1.6 mm across the above crops, seasons, and simulation methods. Given the uncertainty in the ET estimation by the Eddy-covariance due to non-closure of energy balance in the reported range of 10 to 20%, the deviation of the simulated results from the EC results of -11 to 6% does not seem to be excessive.