Quoted from: http://www.appsolutelydigital.com/ModelPrimer/chapter5_section10.html
The SAC-SMA is a continuous soil moisture accounting model with spatially lumped parameters that simulates runoff within a basin. The model divides the basin into lower and upper zones at different depths, and defines the distribution of moisture, i.e., tension water components (driven by evapotranspiration and diffusion) and free water components (driven by gravitational forces) in each of these two zones via a set of parameters. The model uses precipitation and temperature variables, along with parameters on soil moisture states and the basin’s relative permeability to estimate the amount of water that enters, is stored in, and leaves the basin. Thus, the model estimates several key hydrologic processes including evapotranspiration, percolation, interflow, and different forms of runoff from a basin. The SAC-SMA also has a modeling component to model effects of frozen ground on the rainfall-runoff process. The SAC-SMA model is used for various applications that are mainly streamflow or runoff centric, for example, river forecasting, water supply forecasting, basin hydrologic hazard estimates, and basin climate change assessments. The model is ideal for large drainage basins and uses multiple years of records for calibration. The SAC-SMA model is a key model used by the U.S. National Weather Service River Forecast System (NWSRFS) to issue river forecasts across the country. The model code (written in Fortran) is publicly accessible.
Advantages
- Input precipitation can be customized
- Has a frozen ground component
- Can run at any time interval
- Accounts for spatial variability of forcings, basin characteristics, and a few processes
- Lumped modeling system with capability to model sub basins individually in a large river basin
- Has been widely used in the U.S., with many informative case studies
Limitations
- Not effective for small basins
- No direct connection between soil profile and depths of the basin zones (i.e., lower- and upper- zones)
- Parameters require basin knowledge and understanding
- Requires data for multiple years of records for calibration
Additional Information
SAC-SMA algorithm
SAC-SMA parameters
SAC-SMA calibration procedure
Physically based enhancements
SAC-SMA Fortran code
NWSRFS software download links