"Essentially, all models are wrong, but some are useful."
- George Box

This quote, attributed to Box, a statistician, is frequently cited by modelers, particularly in presentations to non-modelers. The point being that no matter how good a particular model is, it will never be perfect.

Over the last year, I have found myself (a non-modeler) thinking about this quote in response to the fierce criticisms levied at the Chesapeake Bay watershed model. The first came from national agribusiness groups, such as the American Farm Bureau Federation, which are attempting to derail the Bay restoration efforts with false claims about the scientific validity of the Baywide Total Maximum Daily Load; and, more recently, from state agency staff and local governments, some of whom are concerned and confused by the way the model seems to be performing at smaller scales.

So, the question is not whether the model is "wrong," but whether it is "useful" in helping to guide Bay pollution cleanup strategies. Numerous peer reviews and a recent report by an independent panel of modeling experts convened by the Bay Program's Scientific and Technical Advisory Committee have confirmed the answer is "yes." The model is a scientifically valid tool that can help us develop a road map to a restored Bay.

For more than a decade, Chesapeake Bay Program partners have used the Bay model to guide their cleanup strategies and estimate the progress that has been achieved. In fact, the current Baywide pollution caps specified in the TMDL are remarkably similar to the previous restoration goals established in 2003 - this, despite the many changes that were made to the model in an ongoing effort to improve the underlying science.

We have known for almost a decade what we need to do to clean up our streams, rivers and the Bay - yet, now, when "the rubber is really meeting the road" - many of the discussions about the Bay cleanup have changed from "how can we implement the necessary practices?" to nonproductive debates about the accuracy of the model.

This is not meant to dismiss concerns, particularly from some local governments who are becoming keenly aware of the task that lies ahead. Bay jurisdictions are reaching out to localities to help them understand their role in Bay cleanup and solicit input for the Phase 2 Watershed Implementation Plans. These plans are intended to build on the state-derived Phase 1 WIPs that accompanied the final TMDL in December 2010.

In response to state requests, the EPA used a slightly revised version of the Bay model to issue the target loads for Phase 2 WIP development. These target loads were issued at the major basin scale (Potomac, Susquehanna, etc.) within each jurisdiction and reflect the same level of effort included by the states in their Phase 1 WIPs. Some states divided up the basin targets to the local (e.g., county) scale and, in some cases, pollution loads and needed reductions changed among the smaller segments, causing confusion for local governments.

As a result, the EPA encouraged the Bay jurisdictions to focus on the implementation of practices at the local level as opposed to trying to achieve a specific numeric local target.

Concurrently, the EPA continues to work with the Bay jurisdictions to refine the model and to do a better accounting of already implemented practices - all examples of the "adaptive management" approach to the Chesapeake's restoration. And in 2017, midway to the 2025 implementation deadline, there will be a formal re-evaluation of progress, the science and the Bay model.

In the meantime, the implementation of the WIPs should move forward. The states and local governments must identify the practices that are possible given existing land uses and the feasibility and cost-effectiveness of implementing the necessary practices. None of this requires local numeric targets. And, there is no danger between now and 2017 of any sector or locality doing too much to reduce pollution.

We know what needs to be done as well as the benefits reducing pollution will have on human health, local job creation and economies as well as and the quality of life for our children and grandchildren.

So, let's stop the debate and focus our efforts on moving forward.