The South Florida Water Management Model (SFWMM) is a regional-scale computer model that simulates the hydrology and management of water resources system from Lake Okeechobee to Florida Bay, covering an area of 7,600 square miles. The model simulates the major components of the hydrologic cycle in South Florida on a daily basis using climatic data for the 1965-2000 period. The components include rainfall, evapotranspiration, infiltration, overland and groundwater flow, canal flow, canal-groundwater seepage, levee seepage and groundwater pumping. The SFWMM incorporates current or proposed water management control structures and current or proposed operational rules. A major strength of this model is its ability to simulate water shortage policies affecting urban, agricultural and environmental water uses in South Florida. The SFWMM is widely accepted as the best available tool for analyzing operational changes to the complex water management system in South Florida and provides information for making the most effective water management decisions.