The Swiss sectorial plan of cropland protections obliges all cantons to protect a certain quota of their best agricultural soils as so-called prime cropland from being built over in the long term. Due to the strong growth of settlements, however, the prime cropland reserves have shrunk considerably. In this project, land use scenarios were modelled to estimate how much prime cropland area might fall victim to new construction zones that are planned for the individual cantons in the following period of comprehensive plans. Due to the model results, it may be difficult for some cantons to obtain their quota of prime cropland. However, the area of possible new construction zones is much smaller than the trend extrapolation of past settlement development would predict.
The best agricultural soils are often found near settlements, as people traditionally settled in agricultural favoured areas. As a rule, urban growth takes place at the expense of particularly fertile soils. In Switzerland, the sectorial plan of cropland protection obliges each canton to protect a certain quota of its most productive agricultural soils as so-called prime cropland from overbuilding. However, in some cantons the prime cropland reserves (the share of prime cropland that exceeds the mandatory quota) have declined considerably over the past 25 years and the question arises as to whether the prime cropland quotas can still be maintained in future.
We modelled the potential loss of prime cropland through new construction zones provided for in the cantonal comprehensive plans and estimated the remaining prime cropland reserves. In addition, we compared the results with scenarios of different socio-economic and population developments.
The model of land use suitability calculated a loss of prime cropland of 3,685 ha for the whole of Switzerland as a result of new construction zones, which almost makes up the area of Lake Zug. Overall, prime cropland reserves throughout Switzerland could shrink by 60% to 2,563 ha. Conversely, the model identified suitable arable land within undeveloped construction zones of 19,548 ha for the whole of Switzerland, which is more than the area of the canton of Appenzell Innerrhoden. There is therefore a certain potential for the cantons to compensate for the loss of prime cropland due to new zoning through outzoning.
Compared to a pure trend extrapolation of settlement growth, the cantons plan to convert far fewer areas to new construction zones. Accordingly, the trend update would also lead to a six times greater loss of prime cropland than our estimates for the current planning period. However, compared to the scenarios for urban development with different population trends, most cantons consume more prime cropland for new construction zones than would be necessary for low population growth. Only in the cantons of Zurich, Zug, Geneva, Aargau and Ticino is the possible prime cropland consumption due to new construction zones lower than the minimum consumption estimated in the scenarios.