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Scenarios
A scenario is a coherent view of a possible future, worked out with a land use model. Scenarios are the common way in land use modelling to deal with an uncertain future.
Looking into the future has fascinated mankind for ages. With the advent of sufficiently powerful personal computers, we no longer need a crystal ball to foresee what our country will look like in, say, 30 years from now. All that is needed now to simulate future spatial developments is a set of spatial data, modelling software and some thoughts on which spatial developments you expect to happen in the coming decades. The latter is, of course, the tricky part. By looking at current developments, we may identify trends that are likely to continue for the coming 5 to 10 years. Yet, looking much further is risky at best, as many uncertainties prevail. Will population growth come to a halt? Will economic development be slow? Will society prefer ecological sustainability or economic prosperity? How will the government try to steer spatial developments? Will they succeed?
Scenarios deal with this uncertainty through several contrasting views of the future, each simulated with the model. No single scenario needs to be the most likely one. Together they show the range of land-use changes that could occur, and a good scenario widens the view of the future rather than predicting it. Xiang and Clarke (2003) stress that scenarios should be plausible yet surprising, and vivid in the information they give.
A scenario changes a land use model through three components:
- Regional demand: the scenario sets how much land each type needs. A scenario with higher population growth, for example, needs more residential land.
- Suitability: the scenario sets how much each location factor counts. Spatial policy enters here as well, because a policy map with a positive or negative weight works as a subsidy or a tax on that location.
- Exogenous developments: planned changes that the scenario places directly on the map, such as a new railway line.
The same components allow a policy alternative: the demand of a scenario stays the same, and only the suitability or the planned developments change. The difference between the two runs then shows the effect of the policy.
A common form is a set of four scenarios on two axes, each axis being a trend that can go either way. The WLO study of 2006 (CPB, MNP & RPB), for example, sets global against regional development and market economy against cooperation. Such a set is not exhaustive. It should be broad enough to show what the main uncertainties mean for land use.
The demand and the suitability of a scenario have to tell the same story. Demand usually comes from sector models that use the same assumptions, while the suitability weights follow from the storyline and take judgement: they cannot be estimated for a future that has not happened (see Calibration and validation).
- The Land Use Scanner demo has four scenarios and a policy alternative, with claims from the WLO 2025 of PBL Netherlands Environmental Assessment Agency.
- Ruimtelijke Verkenning 2023 of PBL describes four scenarios for the Netherlands in 2050.
- The Deltascenarios combine socio-economic and climate developments for water management in the Netherlands.
The Literature page lists more scenario studies with Land Use Scanner.
