Assumptioncondition or factor that is accepted as true or as certain to happen, without proof (Oxford University Press, 2013)
Coupled Model Intercomparison Project 5 (CMIP5)an integrated set of experiments that offer a perspective on simulated climate change and variability from Global Climate Models (GCM). Hundreds of model simulations of the 21st century are available.  FMI:
Endogenous drivera forcing applied to the model that is controlled by factors internal to the basin; something that could be controlled locally, for example by changes in policies
Exogenous driver a forcing applied to the model that is controlled by outside factors (for example a temperature increase determined by a global climate change model)
Integrated decision unit (IDU)an attributed polygon representing a portion of the landscape; a spatial geometry to model both human decisions and successional processes
Modela representation of a real system or process (Konikow & Bredehoeft, 1992)
Private actor/individualFarmers, consumers, interest groups, society generally. Includes “interest groups” or “stakeholders” such as farm lobby, land developers, etc.
Public agentIndividuals whose job it is to enforce laws and manage public resources/assets on behalf of society (dam managers, water masters, water utility staff, state troopers). They also often have valuable expertise about the public institutions they implement or enforce.
Scenario“A scenario is a coherent, internally consistent and plausible description of a possible future state of the world. It is not a forecast; rather, each scenario is one alternative image of how the future can unfold. A projection may serve as the raw material for a scenario, but scenarios often require additional information (e.g., about baseline conditions). A set of scenarios is often adopted to reflect, as well as possible, the range of uncertainty in projections. Other terms that have been used as synonyms for scenario are "characterization", "storyline" and "construction" (Intergovernmental Panel on Climate Change, 2011)
Status Quo scenario The base case, which we use as a comparator for all other scenarios. It adopts mid-range assumptions about climate change, population and income growth, and also assumes that institutions such as water rights, the land-use planning system, reservoir operating rules, forest practices, and urban water pricing continue to operate in their present form.