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DRAINMOD MODIFICATIONS FOR COLD CONDITIONS

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASAE.  VOL. 43(6): 1569-1582 . (doi: 10.13031/2013.3057) @2000
Authors:   W. Luo, R. W. Skaggs, G. M. Chescheir
Keywords:   DRAINMOD, Soil temperature, Freezing, Thawing, Snowmelt

The field hydrology model DRAINMOD was modified to include freezing and thawing, and snowmelt components. Based on daily hydrologic predictions of the original model, the modified DRAINMOD numerically solves the heat flow equation to predict soil temperature. When freezing conditions are indicated by below zero temperatures, the model calculates ice content in the soil profile and modifies soil hydraulic conductivity and infiltration rate accordingly. Recorded precipitation is separated as rain and snow when daily average air temperature is above or below a rain/snow dividing base temperature. Snow is predicted to accumulate on the ground until air temperature rises above a snowmelt base temperature. Soil surface temperature is recalculated when snow cover exists. Daily snowmelt water is added to rainfall, which may infiltrate or run off depending on soil freezing condition. The modified DRAINMOD predictions of soil temperature agreed well with field observations at Plymouth, North Carolina, Truro, Nova Scotia, and Lamberton, Minnesota. Assuming air temperature as the soil surface boundary condition increased the variability of soil temperature predictions at shallow depths, agreement with field measurements was still good. The method of using average air temperature as an indicator to separate snow and rain worked very well for Carsamba, Turkey. At Truro, Nova Scotia, however, the method was not as successful, and several snow events were predicted as rainfall and vice versa. Compared with the original version of DRAINMOD, the modified version predicts fewer drainage flow events in winter months because of snow accumulation on the surface. Subsurface drainage and/or surface runoff resulting from snowmelt are predicted when air temperature rises, the snow melts, and the soil begins to thaw.

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