THE UNDER-APPRECIATED CLIMATE FACTOR IN THE CONSERVATION EFFECTS ASSESSMENT PROJECT

Authors: GARBRECHT, JURGEN; STARKS, PATRICK; STEINER, JEAN

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2006
Publication Date: 8/31/2006
Citation: Garbrecht, J.D., Starks, P.J., Steiner, J.L. 2006. The under-appreciated climate factor in the conservation effects assessment project. Journal of Soil and Water Conservation. 61(4):110A-112A.

Interpretive Summary: Decade long precipitation variations and their impacts on watershed runoff were investigated, and the significance of the findings for the CEAP assessment conservation practices were discussed on the Fort Cobb watershed in central Oklahoma. Decade long precipitation variations displayed a 30 percent change in mean annual precipitation between wet and dry periods, which in turn resulted in a 100 percent change in surface runoff. It was reasoned that soil erosion, transport and agrichemical movement would be similarly affected. Thus, any assessment of effectiveness of conservation practices would depend on the particular precipitation period used in the evaluation. This in turn raised the question as to which precipitation period should be selected for base-line conditions to define effectiveness. Without an agreed upon comparison standard, various numerical values of effectiveness could be obtained for the same conservation practices depending on the precipitation period used. This ambiguity at best limits the usefulness of the CEAP assessment, and at worst fails to meet the intended purpose of CEAP. Persistent precipitation variations can also affect calibration and validation of simulation models used in the assessment of conservation practices. The selection of an “appropriate” base-line precipitation period for the assessment of effectiveness of conservation practices should be debated among policy makers, practitioners, conservation specialist, land owners and climatologists. Until then the calculated effectiveness should be reported with reference to the particular precipitation period and base-line condition used in the model calibration and subsequent assessment.

Technical Abstract: Decade long precipitation variations and their impacts on watershed runoff were investigated, and the significance of the findings for the CEAP assessment conservation practices were discussed on the Fort Cobb watershed in central Oklahoma. Decade long precipitation variations displayed a 30 percent change in mean annual precipitation between wet and dry periods, which in turn resulted in a 100 percent change in surface runoff. It was reasoned that soil erosion, transport and agrichemical movement would be similarly affected. Thus, any assessment of effectiveness of conservation practices would depend on the particular precipitation period used in the evaluation. This in turn raised the question as to which precipitation period should be selected for base-line conditions to define effectiveness. Without an agreed upon comparison standard, various numerical values of effectiveness could be obtained for the same conservation practices depending on the precipitation period used. This ambiguity at best limits the usefulness of the CEAP assessment, and at worst fails to meet the intended purpose of CEAP. Persistent precipitation variations can also affect calibration and validation of simulation models used in the assessment of conservation practices. The selection of an “appropriate” base-line precipitation period for the assessment of effectiveness of conservation practices should be debated among policy makers, practitioners, conservation specialist, land owners and climatologists. Until then the calculated effectiveness should be reported with reference to the particular precipitation period and base-line condition used in the model calibration and subsequent assessment.