Evaluating the adequacy-for-purpose of downscaling methods and products

How should downscaling methods, and the products of downscaling, be evaluated? An adequacy-for-purpose approach attempts to determine whether a method or product can be used successfully for specific purposes of interest. Purposes can take various forms: predicting variable X in region R with a specified level of accuracy, guiding a particular policy decision, etc. Depending on the purpose, different tests or checks will be performed and different levels of performance, on different metrics, will be deemed acceptable. A product that is grossly inaccurate in some respects may nevertheless be entirely adequate for the purpose at hand. Likewise, higher-resolution products are not necessarily more adequate (or fit); it depends on whether they provide the information required for the purpose of interest and in a way that can be interpreted and employed by users.