The report by the Parliamentary Commissioner for the Environment, Simon Upton, said Overseer was designed for farmers to calculate nutrient loss but has since been adopted by councils as a regulatory tool.
To ensure it was performing as required, Upton said in a statement that regional councils needed to be confident in the data Overseer provides.
“To help build confidence there needs to be more transparency around how the model operates.
“Any model operates with a measure of uncertainty. That’s normal. The question is whether the level of uncertainty is an acceptable one.
“Confidence in Overseer can only be improved by opening up its workings to greater scrutiny.
“It will take time to improve Overseer and provide transparency around how it operates. In the meantime, regional councils can continue to use it, but they need to be aware of its limitations.”
He recommended an independent review of Overseer that subjects it to sensitivity and uncertainty analysis, increased transparency around how the model works and regional councils be given official guidance on how Overseer works.
