For the more information about water resources in the National Park Service, please visit http://www.nature.nps.gov/water/.


Reference Conditions and Reference Values

As stated in a dated but still informative U.S. Forest Service fact sheet:

Reference values come in a wide variety of names (benchmark, standard, trend, threshold, desired future condition, norm); but all refer to a comparison to which an indicator can be examined or gauged. The reference value gives a point of reference to help interpret what we know about an indicator; to force discussion about what the measurement of an indicator is telling us; to help us assess whether we are moving in the desired direction and at the right pace; and, to help identify what other things interact with or are affected by that indicator.

...Reference values help us evaluate how we are doing; consequently, their utility critically hinges on the rationale for what we choose as the bases of these values. Reference values can be formed on a variety of different kinds of bases from current conditions to legal standards to historic range of variation. All present potentially logical foundations for forming reference values.

Consistent with the above, NPS has adopted a pragmatic approach to defining and applying reference conditions and values in the context of NRCAs. While it is often appropriate to frame reference conditions in terms of unaltered (pristine) natural conditions, this is not a requirement. While it is usually desirable to express reference values in precise quantitative terms, this is not a requirement. Instead, parks and study investigators are encouraged to frame reference conditions/values in practical, useful terms that reflect currently available data and our interpretations and expert judgments about those data. For example, reference conditions can be framed in terms of regulatory or program standards, historical data, data from relatively undisturbed sites, predictive models, or expert opinion. Embedded in this practical approach is the premise that it is acceptable to revisit and refine reference conditions and values over time—especially as we develop new data and insights about park resources, their conditions, and the factors influencing those conditions.

National guidance on this subject can be stated in very simple terms. At a minimum, all NRCAs must use logical and clearly documented forms of reference conditions and values. Beyond this minimum requirement, individual parks can choose to "raise the bar" and take a more rigorous or formalized approach to defining and quantifying reference conditions/values in their project. For an example of a more formalized approach, see the information and links posted on the EPA website.

In cases where a park has already determined aspects of their 'desired conditions' or 'management targets' through specific park planning and management steps, they can be clearly documented as such and used as reference conditions/values in that park's NRCA project.

For citation purposes, the NRCA Program and a number of other NPS planning and science programs use this formal definition:

Reference Condition: A quantifiable or otherwise objective value or range of values for an Indicator or Specific Measure of Condition that is intended to provide context for comparison with the Current Condition values. The Reference Condition is intended to represent an acceptable resource condition, with appropriate information and scientific or scholarly consensus. The Reference Condition might be based on a regulatory or program standards, historical data, data from relatively undisturbed sites, predictive models, or expert opinon.

Last Updated: July 20, 2012