Modelling the potential impact of New Zealand’s freshwater reforms on land-based Greenhouse Gas emissions

The National Policy Statement for Freshwater Management (NPS-FM) establishes the need to set and manage water resources within limits. This report is the first national assessment of the indirect impacts of the NPS-FM on New Zealand’s greenhouse gas emissions (GHGs). The water quality improvement aspect of New Zealand’s freshwater reforms are expected to drive significant changes in land and water management across the country. Emissions benefits through the freshwater reforms could potentially result in significant savings for New Zealand by starting the transition to low emissions in the agricultural sector and helping to achieve New Zealand’s overall climate goals. For farmers, changes in land use and management to meet water quality targets will reduce their potential future exposure to needs to reduce GHG emissions. GHG emissions reductions are a combination of reduced emissions through changes in management and de-stocking and increased carbon sequestration associated with planting riparian buffers or afforesting part of the farm. Key results are that without land use change, agricultural GHGs (primarily methane and nitrous oxide) could be reduced by 2.4% or 0.82 million metric tonnes of carbon-dioxide equivalent per annum (MtCO2e/yr) along with an additional 0.11 MtCO2e of forest carbon sequestration as a result of planting riparian buffers and pole planting for erosion control (for a net reduction of 0.92 MtCO2e/yr or 13%). If afforestation is perceived to be a feasible freshwater mitigation option, up to 800 000 ha of additional trees could be planted, thereby increasing carbon sequestration by 5.4 MtCO2-e/yr. In this case gross (net) GHGs could be reduced by 2.9 (8.2) MtCO2e/yr, primarily through reduction in stock numbers and increases in forest carbon sequestration. This option could reduce net emissions by nearly 80%. The majority of the emissions impact occurs in the sheep and beef sector, with a gross (net) reduction of 0.61 (0.72) MtCO2e/yr. Nitrogen targets most strongly drive on-farm GHG reductions for all the modelled scenarios that limit mitigation to on-farm changes. This is primarily because actions to mitigate N are most closely related to practices that can also mitigate GHGs (e.g. stock management).