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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #114337
Title: AN ENERGY BUDGET APPROACH TO SIMULATE SNOW MELT AND SOIL FROST DEPTH

Author
item LIN, CHUN - WASHINGTON STATE UNIV
item McCool, Donald
item Flanagan, Dennis
item Sharratt, Brenton

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 4/2/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Water erosion models are used to design crop and land management systems to prevent soil degradation by erosion and runoff pollution by the resulting sediment. Proper simulation of winter hydrology is crucial to satisfactory performance of water erosion models in cold regions. Evaluation of WEPP (Water Erosion Prediction Project) of USDA-ARS indicated it predicted longer soil freezing periods and deeper frost depths than actually observed. Thus it became necessary to modify or replace the current winter subroutines in order to improve performance of WEPP. An energy budget approach was selected and tested for its potential in replacing the winter subroutines in WEPP. This approach has been used to model snow pack development and snow melting and the occurrence of soil freezing. However, it has not been used previously to predict soil frost depths. The energy budget concept was further developed to predict hourly and daily variation of soil frost. It is based on an energy balance composed of four components, net radiation, latent heat, sensible heat and the heat flow through the land surface. In addition, other significant energy sources/sinks were included, such as the energy associated with condensation in snow or soil. All demands and supplies of energy components are assumed balanced at the end of every time step. Therefore if the total value of all energy components is negative, meaning there is an energy deficit, soil freezing will occur to compensate this energy difference; the frost increment is determined by the quantity of this energy difference. Likewise, frozen soils will thaw when positive energy exists. Results show this approach satisfies our goal of improving the winter hydrology routines of WEPP and has flexibility for future improvements in the model.

Technical Abstract: Simulation of winter hydrology is a crucial factor affecting the performance of water erosion models in cold regions. Evaluation of WEPP (Water Erosion Prediction Project) indicated the winter subroutines in this model predict longer soil freezing periods and deeper frost depths than actually observed. It was thus necessary to seek another approach to predict soil frost formation to increase the overall performance of WEPP. An energy budget approach was selected and tested for its potential in replacing the winter subroutines in WEPP. The energy budget approach has been used to model snow pack development and snow melting and to predict the occurrence of soil freezing. However, it has not been used to predict soil frost depths. This project further develops the energy concept to predict temporal variation of soil frost depth. It is based on an energy balance that considers net radiation, latent heat, sensible heat and the heat flow through the land surface. Our first effort was to quantify each energy component on an hourly or daily basis. In addition, other significant energy sources/sinks should be included into this framework if they can be identified and quantified, such as the energy associated with condensation in snow or soil. All demands and supplies of energy components are assumed balanced at the end of every time step. Therefore if the total value of all identified energy components is negative, meaning there is an energy deficit, soil freezing will occur to compensate this energy difference; the frost increment is determined by the quantity of this energy difference. Likewise, frozen soils will thaw when positive energy exists during a calculation interval. The simulation results show this approach satisfies our goal and has flexibility for future improvements.