Implementing the role of reservoirs in the CTSM land surface model

By now, humans have constructed more than 45 000 large reservoirs across the globe. These reservoirs have large impacts on freshwater processes and resources. However, so far the impact of reservoirs on climate remains largely unknown, as they are typically not represented in current earth system models. This is remarkable, as two-way interactions between reservoirs and climate is likely to impact future water availability. Here we present the implementation of the role of reservoirs in the Community Terrestrial Systems Model (CTSM), a land surface model, thereby accounting for (i) the increase in lake area due to reservoir construction and (ii) human operations regulating dam outflow. To this end, we allow lake area to expand in the model, while ensuring that the surface energy and mass balances remain closed. We use reservoir and lake extent data provided by the Global Reservoir and Dams (GRanD) and HydroLAKES data sets. Second, we implement a reservoir operation parametrisation to simulate human management at the reservoir outlet. By conducting coupled simulations with the Community Earth System Model (CESM), we will evaluate the added value of reservoir representation for the Earth System Model performance. This study is an important step towards incorporating human water management in Earth System Models.