1. General Model Information

Name: Elakala Rangeland Hydrology and Yield Model

Acronym: ERHYM

Main medium: terrestrial
Main subject: biogeochemistry, hydrology
Organization level: ecosystem
Type of model: compartment model
Main application:
Keywords: grasslands, water-balance, yield indices, evapotranspiration, soil-water-content, capacity cascade soil water model, curve-number-runoff


J. Ross Wight
Range Scientist
USDA-ARS800 Park Blvd.Suite 105Boise, ID 83712
Telephone : 208-334-1363
FAX : 208-334-1502



ERHYM - II is a deterministic simulation model which simulates daily water-balance and calculates annual yield indices based on the ratio of actual to potential transpiration. The model runs on a daily time step with daily inputs of maximum and minimum air temperatures and solar radiation. Water added to the soil profile is the difference between precipitation and runoff. The SCS curve number procedure as described in CREAMS is used to estimate runoff. As each soil layer is filled to its water holding capacity, water is cascaded down to the next soil layer. When the profile is full, surplus water becomes drainage.

Potential ET is calculated by the Jensen-Haise method. Actual soil and plant evaporation are based on potential ET, soil water content, average site yield, and a relative growth curve. A soil temperature routine from EPIC and the maximum-minimum air temperature and solar radiation generating routines from SPUR are included.

Input data include daily precipitation, maximum and minimum air temperatures and solar radiation, field capacity and permanent wilting water contents for each soil layer, initial soil water content, average site herbage yield at peak standing crop, and dates for start of growing season, peak standing crop, and end of growing season. The model calculates daily values of potential and actual soil and plant evaporation from each soil layer, daily soil water contents, and cumulative actual and potential transpiration. The spatial scale is range site specific.

II. Technical Information

II.1 Executables:

Operating System(s): DOS

II.2 Source-code:

Programming Language(s): BASIC

II.3 Manuals:

II.4 Data:

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

III.2.2 Output

IV. References

Wight, J. R. 1987: ERHYM-II: Model description and user guide for the BASIC version. U. S. Department of Agriculture, ARS No. 59
Wight, J. R. and R. J. Hanks. 1981: A water-balance, climate model for range forage production. J. Range Mangement, 34:307-311
Wight, J. R. and E. L. Neff. 1983: Soil-vegetation-hydrology studies, Vol. II A User Manual for ERHYM: The Elakala Rangeland Hydrology and Yield Model. USDA-ARS, Agricultural Research Results, AR-W-29

V. Further information in the World-Wide-Web

VI. Additional remarks

The ERHYM - II model could be used to quantify the impacts of managementactivities, conservation measures, and projected global changes on westernUnited States grasslands.
Last review of this document by: T. Gabele: 07.07. 1997 -
Status of the document:
last modified by Tobias Gabele Wed Aug 21 21:44:42 CEST 2002

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