Modeling evapotranspiration for irrigation water management in a humid climate

Authors: Anapalli, Saseendran; Fisher, Daniel; Reddy, Krishna; RAJAN, NITHYA - Texas A&M University; PINNAMANENI, SRINIVASA - Department Of Energy

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2019
Publication Date: 8/28/2019
Citation: Anapalli, S.S., Fisher, D.K., Reddy, K.N., Rajan, N., Pinnamaneni, S.R. 2019. Modeling evapotranspiration for irrigation water management in a humid climate. Agricultural Water Management. 225:105731. https://doi.org/10.1016/j.agwat.2019.105731.
DOI: https://doi.org/10.1016/j.agwat.2019.105731

Interpretive Summary: Rapid groundwater declines in the Mississippi river valley aquifer is an emerging problem in irrigated agriculture in the Lower MS Delta region. This observed decline has been mainly attributed to unscientific water withdrawals, beyond the aquifer recharge rates, for crop irrigations. Accurate information on water requirements of various crops grown in this region today is essential for developing checking further aquifer decline by adopting environmentally and economically sustainable water management practices. In this direction, in this pioneering study, scientists with the USDA ARS Crop Production Systems Research Unit, Stoneville, MS, and Texas A&M University, TX, undertook a study to measure water requirements of corn, soybean and cotton in clay dominated soils in farm-scale fields in the Lower Mississippi (MS) Delta, USA. Using these data collected, we also calibrated and developed a cropping system simulation model (RZWQM, USDA ARS) for its accuracies in developing similar crop water requirement information across all the soils, climates, and farming locations in the Delta region. Our study indicates that the model is suitable for generating crop irrigation water requirement information for water resources planning, allocation, or management applications in the Delta region, in the event measured data are lacking.

Technical Abstract: Quantifying evapotranspiration (ET, consumptive crop water requirement) is critical to managing limited water resources for crop irrigations. Agricultural system simulation models that realistically simulate the ET processes are potential tools for integration, synthesis, and extrapolation of location-specific water management research data across soils and climates for limited-water management in agriculture. The objective of this investigation was to evaluate the accuracy of Root Zone Water Quality Model v2.0 (RZWQM2) simulated ET against ET measured in corn, soybean, and cotton cropping systems in a predominantly clay soil under humid climate in the Lower Mississippi (MS) Delta, USA, in 2016, 2017, and 2018. Energy balance (EB) and eddy covariance (EC) methods were used for measuring ET. The RZWQM2 parameters calibrated in previous studies at the location were used in the simulations. Potential evapotranspiration (PET) in the model was simulated using an extended approach based on the Shuttleworth and Wallace (SW) model. Water infiltration into the soil was simulated using the Green and Ampt approach, and its further movement in soil layers and contributions to soil evaporation using the Richard’s equation. Across the three crops and their crop-seasons, simulated daily ET deviated from EC and EB estimates with RMSEs between 0.09 and 0.14 cm and RRMSEs between 21 and 37%. On a weekly basis, accuracies in simulated ET (ETS) improved significantly with RRMSEs between 9 and 17%, and on a seasonal basis RRMSEs were between -9 and 11%. The imbalance in incoming and outgoing energies accounted in the EC system varied between 2 to 12%; taking this uncertainty in estimated ET into account, the accuracies in weekly and seasonal ET simulations were reasonable for their use in irrigation management at these time-scales.