Abstract
In the semi-arid Texas High Plains, the underlying Ogallala Aquifer is experiencing continuing decline due to long-term pumping for irrigation with limited recharge. Accurate simulation of irrigation and other associated water balance components are critical for meaningful evaluation of the effects of irrigation management strategies. Modelers often employ auto-irrigation functions within models such as the Soil and Water Assessment Tool (SWAT). However, some studies have raised concerns as to whether the function is able to adequately simulate representative irrigation practices. In this study, observations of climate, irrigation, evapotranspiration (ET), leaf area index (LAI), and crop yield derived from an irrigated lysimeter field at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas were used to evaluate the efficacy of the SWAT auto-irrigation functions. Results indicated good agreement between simulated and observed daily ET during both model calibration (2001–2005) and validation (2006–2010) periods for the baseline scenario (Nash-Sutcliffe efficiency; NSE ≥ 0.80). The auto-irrigation scenarios resulted in reasonable ET simulations under all the thresholds of soil water deficit (SWD) triggers as indicated by NSE values > 0.5. However, the auto-irrigation function did not adequately represent field practices, due to the continuation of irrigation after crop maturity and excessive irrigation when SWD triggers were less than the static irrigation amount.
Highlights
Hydrologic models such as the Soil and Water Assessment Tool (SWAT) [1], AgriculturalPolicy/Environmental eXtender (APEX) [2], and European Hydrological System Model MIKE SHE [3], are widely used for assessing the impacts of best management practices at various spatial scales
The auto-irrigation function did not adequately represent field practices, due to the continuation of irrigation after crop maturity and excessive irrigation when soil water deficit (SWD) triggers were less than the static irrigation amount
The accurate simulation of water balance processes and their subsequent impacts on plant growth depend on quality environmental and management inputs
Summary
Hydrologic models such as the Soil and Water Assessment Tool (SWAT) [1], AgriculturalPolicy/Environmental eXtender (APEX) [2], and European Hydrological System Model MIKE SHE [3], are widely used for assessing the impacts of best management practices at various spatial scales. Hydrologic models were calibrated for streamflow using measured data at the watershed outlet [4]. A limited number of studies have used measured evapotranspiration (ET) for calibrating hydrologic models [5,6,7]. Wellen et al [4] found that in 96% of studies, models were calibrated against measured streamflow, and in the remaining 4% of studies, models were calibrated using measured surface runoff. They found that none of the studies evaluated the ability of the model to simulate any other hydrologic parameters
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