Using Overseer in fresh water management 

Because Overseer is the only tool available to land managers in New Zealand capable of estimating long-term average nutrient losses from farms it is used by some Regional Councils to support an effects-based approach to managing fresh water as part of the government’s National Policy Statement for Freshwater Management.

Guidance on the use of Overseer in fresh water regulation

Being driven by a complex science model and built as a decision support tool to assess future management options means that there have been many challenges in its application in a regulatory setting.  
After a decade of experience (often contentious) in using Overseer in resource management planning, we commissioned Enfocus to produce a high-level review on the actual and potential use of Overseer in water quality management. View the report Using Overseer in Water Management Planning, October 2018.
We hope that this independent report will further inform the conversation with decision makers on the best ways to achieve the outcomes sought in the National Policy Statement – Freshwater management using outputs from Overseer.

Key messages from the report are that:

  • Overseer models long term annual average losses, not annual actual losses.
  • Using Overseer to model annual compliance with absolute N loss limits, is a high-risk approach, that maximises uncertainty associated with modelling results.
  • There are risks in using Overseer in a pass/fail regulatory context because Overseer models and does not measure.
  • Due to the nature of the uncertainties inherent in the model, in a regulatory context Overseer should be used as:
    • one of many tools in a more comprehensive water management tool box. Overseer analysis and data is only part of the picture in diffuse discharge management and should be supported by measurement and monitoring of effects on water quality and other planning tools.
    • a safe harbour option or to assess compliance based on relative change from a modelled baseline. Lower risk options include using Overseer values as a trigger for closer scrutiny of farm operations or assessing the proportional change over time from earlier “baseline” files.
  • Overseer is a decision-support rather than decision-making tool.
This report follows the Freeman report (August 2016) which presents technical details around the use of Overseer in regulation and was delivered with two other reports to support use by Regional Councils.

Guidance Reports:

  1. September 2015: Technical Description of OVERSEER for Regional Councils (AgResearch) 
  2. July 2015: Stocktake of Regional Council Uses of OVERSEER (Aspiring Environmental)
  3. August 2016: Using OVERSEER in Regulation (Freeman Environmental Limited)  

Overseer's role in a low emissions economy

Agricultural greenhouse gas emissions are not yet regulated in New Zealand, however there is a strong national commitment to reduce our climate impact and growing interest in monitoring emissions from the sector.
Overseer estimates methane, nitrous oxide and carbon dioxide emissions at a farm level, and produces a product footprint for the farm. Overseer includes most mitigation options for reducing GHG from agriculture.
We are working closely with scientists and across the sector to continue to improve model so it can support the sector should further monitoring requirements come in to play.

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