1. General Model Information


Acronym: BROOK

Main medium: terrestrial
Main subject: hydrology, forestry, agriculture
Organization level: landscape , ecosystem
Type of model: partial differential equations (finite differences)
Main application:
Keywords: snow, soil water, precipitation, richards equation, temperature, cutting effects, evapotranspiration, stream flow


C. Anthony Federer
Compass Brook
P.O. Box 96
Kearsarge NH
Email: tony at ecoshift.net

Phone: 603-356-6769


Federer, C. A. and D. Lash


Brook is a hydrological model that simulates snow accumulation, soil water and streamflow from daily precipitation and temperature. The original version of this model was developed in the late 1970s (Federer and Lash, 1978). BROOK2 is a newer version used extensively for teaching and research of snow-soil-streamflow dynamics.

Brook is a deterministic model that looks at hydrologic dynamics at the watershed level. The model contains several water storage compartments: snow, root zone, unsaturated zone below the root zone and groundwater. Input of the model is daily mean temperatures and precipitation. Snowmelt by degree-day factor is adjusted for by leaf area index (LAI) and stem area index (SAI).

BROOK90 contains major modifications to the state equations in the model. For example, potential transpiration and soil evaporation are calculated using the Shuttleworth-Wallace equations and vertical water movement is calculated using a modified Clapp-Hornberger relation. Input required for BROOK90 differs slightly form the earlier versions. Weather information for example must include daily maximum and minimum temperatures, and wind speed. Several additional parameters are needed, including: soils water properties, and stomatal response parameters.

[BROOK90 Flow Chart]

BROOK90 simulates the land phase of the precipitation evaporation streamflow part of the hydrologic cycle for a point or for a small, uniform (lumped parameter) watershed. There is no provision for spatial distribution of parameters in the horizontal. There is no provision for lateral transfer of water to adjacent downslope areas. Instead, BROOK90 concentrates on detailed simulation of evaporation processes, on vertical water flow, and of local generation of stormflow. Below ground, the model includes one to many soil layers, which may have differing physical properties.

BROOK90 has been designed to be applicable to any land surface. The model has numerous parameters, but all parameters are provided externally, are physically meaningful, and have default values. Parameter fitting is not necessary to obtain reasonable results. However, a procedure is described for modifying important parameters to improve the fit of simulated to measured streamflow.

BROOK90 is designed to fill a wide range of needs: as a research tool to study the water budget and water movement on small plots, as a teaching tool for evaporation and soil water processes, as a water budget model for land managers and for predicting climate change effects, and as a fairly complex water budget model against which simpler models can be tested.

Evaporation has five components: evaporation of intercepted rain (IRVP), evaporation of intercepted snow (ISVP), evaporation from snow (SNVP), soil evaporation (SLVP) from the top soil layer, and transpiration (TRANI) from each soil layer that contains roots. Potential evaporation rates are obtained using the Shuttleworth and Wallace (1985) modification of the Penman-Monteith approach. Evaporation of intercepted rain or snow is calculated with a canopy resistance of zero and aerodynamic resistances based on canopy height, coupled with a canopy capacity and an average storm duration. For potential transpiration, canopy resistance depends on maximum leaf conductance, reduced for humidity, temperature, and light penetration. Aerodynamic resistances are modified from Shuttleworth and Gurney (1990); they depend on leaf area index (LAI), which can vary seasonally, and on canopy height, which determines stem area index (SAI). Soil evaporation resistance depends on soil water potential in the top soil layer. Actual transpiration is the lesser of potential transpiration and a soil water supply rate determined by the resistance to liquid water flow in the plants and on root distribution and soil water potential in the soil layers.

Snowmelt is based on a degree day factor and accounts for snowpack temperature and liquid water content. The factor is modified for canopy cover as determined by LAI and SAI. Snow evaporation or condensation depends on the aerodynamic resistances and the vapor gradient; however, an arbitrary reduction factor is required.

Net throughfall plus snowmelt may 1) infiltrate into the soil matrix of the surface horizon (INFLI(1)), 2) infiltrate directly to deeper horizons via vertical macropore flow (INFLI), 3) go immediately to streamflow via vertical macropore flow followed by downslope pipe flow (BYFLI), or 4) go immediately to streamflow via impaction on a variable saturated source area (SRFL). Water in the soil matrix (SWATI) moves vertically according to the Darcy Richards equation for saturated or unsaturated flow. A downslope flow component may also be simulated (DSFLI). Integration of these rates is by explicit forward difference (Euler), but with a variable iteration time step that limits changes in layer water content and in potential gradients. The relationships among matric potential, soil water content, and hydraulic conductivity are parameterized by a modified Clapp-Hornberger formulation with values given at field capacity. Water is added to groundwater by gravity drainage from the deepest soil layer. The groundwater component of streamflow (GWFL) is simulated as a fixed fraction of groundwater each day. A fixed fraction of the groundwater outflow may be deep seepage. Simulated streamflow is the sum of SRFL, BYFL, DSFL, and GWFL. This can be compared with measured streamflow if that is available.

Author of the abstract: Derived from a previous Home page of BROOK models

BROOK2 is designed for forest land, has only a single soil layer, and has few parameters. BROOK90 is applicable to any land surface, can have from one to many soil layers, and has many physically-meaningful parameters.

II. Technical Information

II.1 Executables:

Operating System(s): Windows (VB)
BROOK90 is available in 3 versions:
Version 4.4.e for Windows XP/VB6 (including source code)
Version 3.4a for Windows 95/98/NT/VB3
Version 3.1 F/Q Windows/VB3 (including source code)f
Download from http://home.roadrunner.com/~stfederer/brook/downloads.htm

II.2 Source-code:

Programming Language(s): FORTRAN (Brook2), Visual Basic(Brook90)
Download (Brook90): see: Brook90 download page
Download (Brook2): source code (Fortran 77)

II.3 Manuals:

see Brook documentation

II.4 Data:

See download page: http://home.roadrunner.com/~stfederer/brook/downloads.htm

III. Mathematical Information

III.1 Mathematics

III.2 Quantities

III.2.1 Input

BROOK90 can be run with only optional inputs are:

III.2.2 Output

IV. References

Federer, C. A. and D. Lash. 1978. BROOK: a hydrologic simulation model for eastern forests.
University of New Hampshire Water Resource Research Center Research Report 19. 84p.

Federer, C. A. and D. Lash. 1978, Simulated stream flow response to possible differences in transpiration among species of hardwood trees.
Water Resources Research.14:1089-1097.

Hornbeck, J.W., C.A. Federer, and R.S. Pierce. 1987. Effects of whole-tree clearcutting on streamflow can be adequately estimated by simulation. Inter Assoc Sci Hydrol Pub 167:565-573.

Hunt, E.R., S.W. Running, and C.A. Federer. 1991. Extrapolating plant water flow resistances and capacitances to regional scales. Agric For Meteorol 54:169-195.

Federer, C.A., D.E. Turcotte, and C.T. Smith. 1993. The organic fraction-bulk density relationship and the expression of nutrient content in forest soils. Can J For Res 23:1026-1032.

Lawrence, Gregory B. Mark B. David and Walter C. Shortle. 1995. A new mechanism for calcium loss in forest-floor soils. Nature 378: 162-165.

Ollinger, S.V., J.D. Aber, C.A. Federer, G.M. Lovett, and J.M. Ellis. 1995. Modeling physical and chemical climate of the northeastern United States for a geographic information system. USDA Forest Service Gen Tech Rep NE-191, 30 p.

Federer, C.A. 1995. BROOK90: a simulation model for evapotranspiration, soil water, and streamflow, Version 3.1. Computer freeware and documentation. USDA Forest Service, PO Box 640, Durham NH 03824.

Federer, C.A., C. Vörösmarty, and B. Fekete. 1996. Intercomparison of methods for calculating potential evaporation in regional and global water balance models. Water Resour Res 32:2315-2321.

Vörösmarty, C.J., C.A. Federer, and A.L. Schloss. 1998. Potential evaporation functions compared on US watersheds: Possible implications for global-scale water balance and terrestrial ecosystem modeling. J Hydrol 207:147-169.

V. Further information in the World-Wide-Web

VI. Additional remarks

A major purpose of the model is to study the effects of changing the ratios of evergreen to deciduous forests which might occur under different global change scenarios.
Last review of this document by: J. Bierwirth: 08.03.2001 --
Status of the document:
last modified by Joachim Benz Sat Jan 17 21:24:10 CET 2009

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