Virtual watersheds: simulating the water balance of the Rio Grande Basin

Managers of water resources in arid and semi-arid regions must allocate increasingly variable surface water supplies and limited groundwater resources. This challenge is leading to a new generation of detailed computational models that can link multiple sources to a wide range of demands. Detailed computational models of complex natural-human systems can help decision makers allocate scarce natural resources such as water. This article describes a virtual watershed model, the Los Alamos Distributed Hydrologic System (LADHS), which contains the essential physics of all elements of a regional hydrosphere and allows feedback between them. Unlike real watersheds, researchers can perform experiments on virtual watersheds, produce them relatively cheaply (once a modeling framework is established), and run them faster than real time. Furthermore, physics-based virtual watersheds do not require extensive tuning and are flexible enough to accommodate novel boundary conditions such as land-use change or increased climate variability. Essentially, virtual watersheds help resource managers evaluate the risks of alternatives once uncertainties have been quantified.