Other events that could disrupt delivery of imported surface water include a breach in the levees in the Sacramento-San Joaquin Delta in northern California and extreme droughts. Extreme droughts would also limit the capture and reuse of local runoff and could impair the quality of imported water. The USGS used a groundwater simulation model to generate response functions representing the basin-wide hydraulic impacts of different scenarios of disruptions and utilisation of groundwater during emergencies. These response functions were coupled with cost coefficients, a discount rate, and a probabilistic representation of the likely additional groundwater use to estimate the emergency benefits of groundwater management strategies.