The Thornthwaite water balance (Thornthwaite, 1948; Mather, 1978; 1979)
uses an accounting procedure to analyze the allocation of water among various
components of the hydrologic system. Computations of monthly water-balance
components of the hydrologic cycle are made for a specified location.
The model can be used as a research tool, an assessment tool, and as a tool for
classroom instruction. It also demonstrates basic principles about modeling
with OMS3, specifically temporal advancement within a model.
Figure 1: Waterbalance Model Schematic
Inputs to the model are monthly temperature and precipitation. Outputs include monthly potential and actual
evapotranspiration, soil moisture storage, snow storage, surplus, and runoff.
The schematics below shows the components and connectivity of the Thornthwaite
water balance model. The boxes represent the components, the arrows show the
data-flow between components.
Figure 2: Thornthwaite Component Schematic
The model processes monthly climate input (precipitation, temperature) and produces
output for runoff and other state variables. It has only three parameter: latitude, soil
moisture capacity, and a runoff factor.
Running the Thornthwaite Model step by step
1.Get the project.
Downlad the zip package; unpack it to the local hard drive. It contains all files
to run Thorthwaite, 2.Start the OMS3 modeling console and set the 'Working Directory'
First, start the console.
In the console set the work directory to the folder <INSTALL>/oms3.prj.thornthwaite. Click the blue
folder icon at the top right corner of the window, navigate to the folder <INSTALL>/oms3.prj.thornthwaite
and accept. The file tw.sim should be displayed in the console.
3.Run the Simulation.
The model can be run by pressing the run Button in the console.
4.View the Results.
The Simulation is providing basic graphical timeseries plot that can be shown by pressing the ?? icon in
the console. You should see a graph like:
Thornthwaite, C.W., 1948, An approach toward a rational classification of climate: Geographical Review, v. 38, p. 55–94.
Mather, J.R., 1978, The climatic water balance in environmental analysis: Lexington, Mass., D.C. Heath and Company, 239 p.
Mather, J.R., 1979, Use of the climatic water budget to estimate streamflow, in Mather, J.R., ed., Use of the climatic water budget in selected environmental water problems: Elmer, N.J., C.W. Thornthwaite Associates, Laboratory of Climatology, Publications in Climatology, v. 32, no. 1, p. 1–52.
McCabe, G.J., and Markstrom, S.L., 2007, A monthly water-balance model driven by a graphical user interface: U.S.
Geological Survey Open-File report 2007-1088, 6 pp.