Risk is the likelihood for negative consequences. It is more difficult to estimate or project into the future because of the extra uncertainty expected for future conditions. For future values, there are no observations or measurements, which increases the amount of uncertainty because all values are estimates.

Uncertainty means lack of knowledge. It is especially important to define what is known, how well it is known, and what is unknown when: 1) making simulations with computer models and 2) projecting future values and system responses. For computer simulation, "All models are wrong but some are useful Box and Draper, 1987 p. 474." Consequently, it is important to avoid blindly believing models and to focus on where the simulation results are useful for decision support and hypothesis testing. For future values, there are no observations or measurements, which increases the amount of uncertainty because all values are estimates.

Water resources are natural resources of water that are potentially useful to humans and are thus subject to management and exploitation. Computer modeling utilizes a simplified and reduced depiction of complex and infinite reality to depict the movement and occurrence of water in a system and can provide decision support for water resources management.

Because all models are wrong and the future is inherently uncertain, it is important to implement best practices and techniques to limit and constrain the propagation of model error and uncertainty to simulation results. The negative consequences that will accrue from error and uncertainty propagation are specious decision support for water resources management.