1. Home
  2. Datasets
  3. Pasture production maps ...

Pasture production maps under climate change

Description

Spatial distribution of estimated annual pasture production across New Zealand under climate change scenarios.

A summary of APSIM simulations of a ryegrass/white clover pasture under four different representative concentration pathways (RCPs) and two combinations of irrigation and fertiliser management:

  • No irrigation and no fertiliser
  • Applying irrigation and N fertiliser as required, but limited to 200kgN/ha/year

 

Date: December 2023 Version: v1

Owner: PFR, MWLR, NIWA

Contact: Rogerio Cichota, Plant and Food Research

 

Preview Image

 

Dataset attributes

Spatial extent National. Large lakes and rivers and conservation areas have been excluded
Spatial resolution Productivity surface developed at 100m resolution, based on simulations using 5km climate grid and soil map with a 1:50000 nominal scale
Temporal extent Annual average from 20 years simulations in three time slices: early century (2006 to 2026), mid century (2040 to 2060), and late century (2080 to 2100)
Temporal resolution Annual averages from simulations at daily time steps
Evaluation method (Validation) The accuracy of these results cannot be evaluated as they were produced based on projections to future climate. The APSIM model itself has been extensively validated against observations under historical climate, but the model's sensitivity to factors impacted by climate change have not been fully investigated. Therefore, the results presented in these maps should be used with great caution.
Evaluation result (Numeric)
Evaluation result (Categorical) General preliminary data, low confidence
Uncertainty method
Uncertainty data format (Numeric)
Uncertainty data format (Categorical)

 

Methodology

The pasture production surfaces were derived from biomass accumulation data simulated using the Agricultural Production Systems Simulator (APSIM) model. Simulations were set up in APSIM to describe a continuous ryegrass/white clover mixed pasture under rotational defoliation. The simulation setup included the possibility of applying irrigation, driven by soil moisture status, and nitrogen fertiliser, applied as urea following defoliations depending on soil N status and limited to 200kgN/ha/yr. Defoliations were set to occur whenever pasture biomass reached 2500 kgDM/ha, with further constraints to avoid defoliating in intervals less than 15 days or greater than 60 days. Biomass harvested was accumulated over the year (from July to June) and then averaged across 20 years. These were then averaged across three global circulation models (GCMs) for each RCP scenario and for three time slices: early century (2006-2026), mid century (2040-2060), and late century (2080-2100).
Important to note that these simulations used only ryegrass/white clover and assumed that the management was unimpeded by external factors such as access to machinery, holidays, weather, etc., and there were no restrictions to access water for the irrigated scenario. The model also assumed no inefficiencies on the application of water and N to the field. These were applied homogeneously to the soil, which was also the case for the return of residues and excreta after each defoliations. Moreover, the simulations did not account for pests and diseases nor for nutrient limitations (other than nitrogen).

Daily weather data was sourced from NIWA's downscaled Climate Change projections for CMIP5 (which has the coverage as VCSN data). Simulations were run using data from three GCMs (HadGEM2-ES, CESM1-CAM5, and GISS-EL-R) for each RCP (2.6, 4.5, 6.0, and 8.5).

More details in:
Ministry for the Environment, 2018. Climate Change Projections for New Zealand: Atmosphere Projections Based on Simulations from the IPCC Fifth Assessment. Soil parameters from S-map were provided by Manaaki Whenua (with proxies used over the Fundamental Soil Layer map for areas not covered by S-map).
Note that the soil and weather data were employed 'as given', with no adjusts for factors such as slope, or high water table.

 

Fitness for purpose / limitations

This table indicates whether the dataset is suitable for different types of questions at different scales.

Note: Users should carefully consider their purpose as this dataset may not be suitable.

Operational Absolute Relative Screening/scoping
Block/farm No No No Maybe
Multi-farms(5+) No No Maybe Maybe
Catchment No No Maybe Maybe
National/regional No No Maybe Maybe
Caveat(s) Soil limitations considered in the simulations were limited to water and nitrogen supply and also excluded pests and diseases.

Data and Resources