In this paper, a model-based integrated assessment of the long-term consequences of water erosion in four olive groves with different conditions in Andalusia (southern Spain) is carried out. The assessment is based on a system dynamics model built at hillside scale. The modelling approach tackles common difficulties arising from the relative scarcity of data and the uncertainty of the long term. On the one hand, model results have allowed characterising the nonlinear dynamics of water erosion. On the other, they have showed that positive gross margins may definitively vanish after around 100 years in some olive-growing areas. In spite of this, the adoption by farmers of soil conservation practices is limited. The assessment shows that the loss of yields due to the erosion-caused reduction in soil water availability lead to annual economic losses ranging between 1 and 2.8 € ha−1 yr−1 in the studied rainfed orchards. These losses are completely obscured by the normal fluctuations in economic and production variables, so that they do not give farmers adequate warning of the consequences of non-sustainable soil management.