Protocol for Evaluation and Updates
The purpose of a plan, of any kind, is not to sit on a shelf and collect dust, but rather help chart a clear and coordinated path forward. Plans are composed of a multitude of elements that need to be frequently reevaluated to ensure that they are still applicable and that new knowledge and information is incorporated. The same is true with drought indicators and triggers. New products may become available that provide more utility than past products, or that fill a void that no other existing product could. Thresholds may need to be adjusted to more accurately represent what actually occurred during a drought event, and actions for each of those thresholds may need to be adjusted to reflect improved adaptive capacity or political realities.
There is no right or wrong timeframe for reevaluation, but it should occur on a regular basis and frequently enough that lessons learned can be incorporated while they are still reasonably fresh in users' minds. As an example, the Federal Emergency Management Agency requires that states and local governments update their hazard mitigation plans once every 5 years.