Skip to main content
ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #329878
Title: Evaluation of four parameterization strategies for the APEX model

Author
item SENAVIRATNE, G.M.M.M. ANOMAA - University Of Missouri
item Baffaut, Claire
item LORY, JOHN - University Of Missouri
item UDAWATTA, RANJITH - University Of Missouri
item NELSON, NATHAN - Kansas State University
item BHANDARI, AMMAR - University Of Missouri

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/19/2018
Publication Date: 10/29/2018
Citation: Senaviratne, G., Baffaut, C., Lory, J.A., Udawatta, R.P., Nelson, N.O., Bhandari, A.B. 2018. Evaluation of four parameterization strategies for the APEX model. Transactions of the ASABE. 61(5):1603-1617. https://doi.org/10.13031/trans.12656.
DOI: https://doi.org/10.13031/trans.12656

Interpretive Summary: Computer simulation models are increasingly important for quantifying effects of conservation practices on runoff water quality from agricultural fields. Before they can be used, they need to be parameterized, i.e. their input values need to be specified to reflect the simulated site, and then adjusted within limits so that model results match monitoring data. Four parameterization strategies were tested for the Agricultural Policy/Environmental eXtender (APEX) model to predict event runoff, sediment and total phosphorus (TP) losses on a test watershed. The test dataset was from a field in grain production with winter cover crops (WCC), terraces and a grass waterway (GWW) in Chariton County, Missouri. One parameterization (LC) was obtained through calibration of a nearby tilled field. Two parameterizations, pre-buffer validation (PBV) and buffer validation (BV), were obtained from two fields in no-till grain production with GWW, ~70 miles from the test watershed. The PBV was calibrated using 1993-1998 data; the BV was obtained using 2002-2008 data after installation of in-field contour buffers but failed to simulate sediment loss with sufficient accuracy. The fourth parameterization, best professional judgment (BPJ), was not calibrated. Only parameterizations that correctly simulated runoff, sediment, and TP on their original site (PBV and LC) successfully simulated runoff, sediment and TP in the test watershed. The four parametrizations were then used to estimate 30-yr average annual water quality measures for six scenarios: no practice, WCC, GWW, WCC and GWW, terraces and GWW, and all combined. The two models that correctly simulated runoff, sediment, and TP (PBV and LC) were most similar in both magnitude and range of predicted response. The two others (BV and BPJ) gave significantly different answers in terms of ranking of the practices and potential benefits. The APEX model, when appropriately calibrated, can provide quantitative estimates of runoff, sediment and TP for alternative weather and conservation practice scenarios on landscapes similar to calibration watersheds. These findings should benefit scientists and water resources managers and help them interpret model results depending on how the models were calibrated.

Technical Abstract: Hydrologic models are increasingly important for quantifying effects of conservation practices on runoff water quality from agricultural fields. Four parameterization strategies were tested for the Agricultural Policy/Environmental eXtender (APEX) model to predict event runoff, sediment and total phosphorus (TP) losses on a test watershed. The test dataset (2012-2013) was from a field-scale watershed in grain production with winter cover crops (WCC), terraces and a grass waterway (GWW) in Chariton County, Missouri. One parameterization (LC) was obtained through calibration of a nearby (4.2 km) tilled field-scale watershed using 2012-2013 data. Two parameterizations, pre-buffer validation (PBV) and buffer validation (BV), were obtained from two field-scale watersheds in no-till grain production with GWW, 110 km from the test watershed. The PBV was calibrated using 1993-1998 data; the BV was obtained using 2002-2008 data after installation of in-field contour buffers but failed to meet sediment performance criteria. The fourth parameterization, best professional judgment (BPJ), was not calibrated. Only successfully calibrated parameterizations (PBV and LC) met validation criteria for runoff, sediment and TP for the test watershed. The four parametrizations were then used to estimate 30-yr average annual water quality measures for six scenarios: no practice, WCC, GWW, WCC and GWW, terraces and GWW, and all combined. Validated models (PBV and LC) were most similar in both magnitude and range of predicted response across treatments for runoff, sediment and TP loss. The APEX model, when appropriately calibrated, can provide quantitative estimates of runoff, sediment and TP for alternative weather and conservation practice scenarios on landscapes similar to calibration watersheds.