Water uptake in crop monocultures under the influence of fine root dynamics and plant physiological characteristics is still largely understood as in the active research period of HM Taylor. Taking these principles to mixed cropping systems and agroforestry in a range of climates, however, still yields surprises as the combination of competition and facilitation remains difficult to predict. The (re)inclusion of trees in agricultural production landscapes affects processes from root to watershed scale, with interactions that are hard to unravel experimentally at the relevant spatial and temporal scales. Simultaneous hydraulic redistribution via tree and crop root systems and the local and functional equilibrium responses in fine root dynamics of all plants are essentially understood at process level, but only recently represented in dynamic simulation models. The lecture will provide examples of applications of the WaNuLCAS 3.1 model to early stages of introduction of timber trees into cassava systems on poor soils in Lampung (Indonesia), parkland systems in the dry savannah zone of Burkina Faso, trees of different phenology in Kenya and emerging sylvoarable systems in southern France.