Some problems are too complex to be addressed with all the detail with which they are encountered in reality. Addressing these kinds of problems requires the use of a simplified representation of reality: a model. In the context of water quality, land-use models are used to help anticipate and diagnose problems, estimate the cost of meeting environmental targets, and simulate different policy options to explore their likely impacts.
Among scientists, the formal and frequent use of models is so well established that it is accepted without requiring explanation. However, to those outside the scientific community models can seem like black boxes, and the variety of available models can cause confusion.
Motu is currently compiling a database of rural data as part of our Land Use, Climate Change and Kyoto: Human Dimensions Research to Guide NZ Policy research programme. This data is used in our Land Use in Rural New Zealand (LURNZ) model to estimate and give parameters to the underlying econometric model and the spatial model.
The land-use change module is econometrically estimated from national time series, and then the land use change is spatially allocated using economic and geophysical variables. It is primarily a simulation model that compares the projection to a baseline scenario.
The implications of climate policies are analysed via their effects on commodity prices. LURNZ models land-use in dairy, sheep/beef, plantation forestry, and scrub (regenerating native forest), and treats other rural uses, conservation land and urban areas as exogenous. It also spatially allocates land use change, simulates dairy and sheep/beef production, and simulates greenhouse gas (GHG) emissions and sequestration patterns.