Chapter 10 – Forecasting and Uncertainty Analysis

Most groundwater models are constructed to make science-based forecasts, though a forecast can only reflect what is known at the time of the forecast. A forecast (prediction) is made by modifying the base model ( Chapter 9) to include stresses and other conditions expected to change in the future. Uncertainty about future conditions and inherent uncertainty in the base model impart uncertainty to forecasts. Forecasts encompassing long time periods and those that require a high degree of system characterization will have relatively higher levels of uncertainty. Methods for estimating uncertainty range from best- and worst-case scenarios to complex methods that account for multiple conceptual models. No model forecast should be reported without some estimate of uncertainty that can be conveyed to the decision-maker in an understandable way. Forecast uncertainty is less frequently assessed after the fact through postaudits.