This paper presents a method based on scenario analysis to compare the environmental effects of different
spatial plan policies in a range of possible futures. The study aimed at contributing to overcome two
limitations encountered in Strategic Environmental Assessment (SEA) for spatial planning: poor exploration
of how the future might unfold, and poor consideration of alternative plan policies. Scenarios were developed
through what-if functions and spatial modeling in a Geographical Information System (GIS), and consisted in
maps that represent future land uses under different assumptions on key driving forces. The use of land use
scenarios provided a representation of how the different policies will look like on the ground. This allowed
gaining a better understanding of the policies' implications on the environment, which could be measured
through a set of indicators. The research undertook a case-study approach by developing and assessing land
use scenarios for the future growth of Caia, a strategically-located and fast-developing town in rural
Mozambique. The effects of alternative spatial plan policies were assessed against a set of environmental
performance indicators, including deforestation, loss of agricultural land, encroachment of flood-prone areas
and wetlands and access to water sources. In this way, critical environmental effects related to the
implementation of each policy were identified and discussed, suggesting possible strategies to address them