The overarching goal of this study is to provide a quantitative basis for managing water resources in the semi-arid Tarim Basin in Western China. The increased use of surface water in the upstream of the Tarim River has led to the drying up of a stretch of over 300km, with devastating consequences for the riparian Populus Euphratica forests. To save these valuable ecosystems, the Chinese government initiated the “Ecological Water Conveyance Project”. The goal of this initiative is to stop the decline of the downstream ecosystems by periodically reducing the amount of water diverted for irrigation in the upstream. In order to provide quantitative guidance towards sustainable management, this project integrated ecological data with advanced mathematical modelling of surface water, groundwater and vegetation, using HydroGeoSphere (HGS).