The Ozark Plateaus Groundwater Model: Parameter Effects on Forecast Uncertainty

Groundwater models are increasingly used to inform resource-management decisions. As such, it is important to understand how model uncertainty may affect scenario forecasts, particularly if such forecasts could suggest a wide range of possible management outcomes. In 2014, the U.S. Geological Survey (USGS) began developing a regional model of the Ozark Plateaus aquifer system to quantify groundwater availability and to evaluate impacts of climate variability and water-use changes. Water levels in wells screened in the aquifer system respond relatively rapidly to withdrawals and seasonal fluctuations in hydrologic drivers. Some water-level fluctuations exceed 100 ft, creating the need to lower pumps or drill new wells, and drought periods can cause alarm among water managers for municipal and industrial supply and within agricultural communities. Because of the aquifer system’s sensitivity to these fluctuations, the USGS will conduct linear-based, first-order, second-moment (FOSM) uncertainty analysis to estimate forecast uncertainty and to quantitatively evaluate which parameters have the greatest effect on forecast uncertainty. Complementary analysis based on the assumptions of FOSM will be used to estimate the value of additional information to reduce forecast uncertainty. The uncertainty analyses can be enlightening and often identify areas or parameters within the model that could reduce the range in forecast outcomes.