Representing Human Water Management in a Land Surface Model Using a Supply/Demand Approach

The impact of human water management on river discharge is increasingly viewed as a missing process in Earth system modeling. Models which have attempted to include it are generally at coarse resolution and uncoupled to the atmosphere. We propose to describe human water management at high spatial resolution using ORganizing Carbon and Hydrology In Dynamic EcosystEms concept of hydrological-transfer-units in the routing parametrization. Irrigated areas are linked to river abstraction points using a minimization process. The directed graphs of river flows and adduction network for irrigation is transposed to propagate water demands upstream. Reservoirs and dams are placed along the graph to balance supply and demands in the four chosen water value classes. Dam regulation is assumed to maximize demand satisfaction and dampen floods while respecting the properties of the infrastructure. The developed human water management module is applied to the Yellow River where irrigation and dam regulation are known to have a strong impact. Results show that the impact of human water management is strongly heterogeneous over space. It propagates along the river channels and can be mitigated by the confluence of tributaries. Moreover, the human impact has a strong seasonality due to time varying irrigation demands and the response of dam regulation. A number of uncertainties still remain and affect the simulated river discharge. Nevertheless, the representation of human water management improves the model's behavior in terms of magnitude and intra-annual variations of river discharge, and offers the opportunity to implement anthropogenic processes in the water cycle of Earth System Models.