The overall objective of the “China-Trend-Stream” project is to quantify and understand the processes that have caused the observed historic trends in the Yangtze and Yellow River discharges and to project future trends until 2050. To do this, we propose a 3-year project based on a novel and ambitious, synergetic approach, combining satellite observations, national surveys, in situ measurements and improved modeling. We plan the following workplan: - Improve the simulation of managed ecosystems in China, specifically the effect of management on soil moisture and runoff. Forest plantations, and crop management practice including irrigation will be incorporated into the ORCHIDEE land surface model currently used both by French and Chinese partners. - Improve the simulation of river flow by accounting for reservoirs, floodplains and wetlands This will require new developments in the water routing scheme of ORCHIDEE, combined with the use of SPHY, a detailed catchment model. A unique set of dam management data and river discharge observations will be used for model evaluation. - Attribute past, present and future changes in the water budgets of the Yangtze and Yellow River and their sub-basins, using ORCHIDEE and separate the effects of temperature and rainfall, plants’ response to rising CO2, land-use change and water management change (damming, irrigation). Once evaluated for the past 25 years, future projections of the discharge of both rivers, separating the above-listed driving factors, will be performed until 2050. - Quantify the atmospheric feedbacks affecting Yangtze and Yellow River discharge changes. For this, the ORCHIDEE land surface model will be run “online” coupled to the LMDZ-ZASIA climate model for an ensemble of past and future simulations. The results will allow us to assess for the first time how regional rainfall changes resulting from atmospheric feedbacks modify soil moisture and in turn river discharge trends. - The results acquired during the project will be synthesized into a blueprint for an advanced decadal-scale forecasting system for water resources in China, available to policymakers and other stakeholders. The project will be conducted by complementary French and Chinese teams, who have already collaborated for many years through joint PhD and post-doctorate exchanges. The record of this consortium guarantees the success of the project and the achievement of the project objective of attributing river discharge changes to anthropogenic and climatic drivers.