The WRAP modeling system simulates water resources development, management, regulation, and use in a river basin or multiple-basin region under a priority-based water allocation system. The model facilitates assessments of hydrologic and institutional water availability and reliability in satisfying requirements for municipal, industrial, and agricultural water supply, hydroelectric energy generation, environmental instream flows, and reservoir storage. In WRAP terminology, water use requirements, water control infrastructure, and reservoir/river system operating strategies are called water rights. Basin-wide impacts of water resources development projects and management practices are modeled. Earlier versions of WRAP were designed specifically for water availability and reliability analyses based on the results of a simulation using a monthly computational time step. The 2010 version also includes daily time step modeling capabilities that include flow forecasting, flow routing methods, disaggregation of monthly naturalized flows to daily flows, and simulation of flood control reservoir system operations. Salinity simulation capabilities have also been recently added.