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How climate data impacts the model

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Summary

When blocks are drawn, the location of the block is used to determine the annual rainfall, temperature and potential evapotranspiration (PET) for the block from a NIWA 30-year climate dataset built into OverseerFM. The model uses default profiles based on the farm’s region/nearest town to calculate daily/monthly rainfall, temperatures and PET.

The following diagram depicts what parts of the model the climate information in OverseerFM impacts. For a full interactive view of the scientific model in its entirety please click here

 

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Impact

Climate has a significant impact on the modelling. Climate is used in the hydrology model to estimate drainage which causes leaching. Climate also affects biological processes such as decomposition, volatilisation and denitrification

Advice

  • Draw blocks to get climate for that location

  • When possible use nearest town for climate profile

Details

If multiple non-contiguous areas of land are drawn for a single block, the climate for each piece of land is taken and then averaged proportionally based on the area of each piece.

Although not recommended, latitude and longitude can be entered to override the location used to lookup climate. The quality of the block drawings does not have any impact on the model, so you can just draw an approximation to get climate data without having to try and find the latitude and longitude for the block.

If a single block has quite different climates, then it might make sense to split it into two blocks if you would like to see how the climate effects the results and therefore consider how you might treat those two pieces of land differently. If that is not an option, then a single block with average climate is fine.

The nearest town or region set for the farm impacts how the average climate values are proportioned over the year. The model works out daily values and uses them to model many of the soil properties and processes that effect nutrient flows within a block. Where it makes sense, use the nearest town as this should give a more accurate representation of the area.

Overseer does not account for small variations or microclimates. We are currently looking to update the regional profiles and climate data set, but it will always be a general representation.

Entering snowfall essentially adds to rain fall for the purposes of modelling.

Fields

  • Average temperature: The average annual temperature for the year. Uses regional profile to infer monthly temperatures from the annual average.

  • Average rainfall: The average annual rainfall for the year. Uses regional profile to calculate daily rainfall for the hydrology and other sub models.

  • Annual PET: A measure of evaporation. Uses regional profile to calculate daily PET which is used to determine water loss in the hydrology model.

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