Daily Evapotranspiration and Soil Moisture Estimates for the Northeastern United States

A.T. DeGaetano, K.L. Eggleston and W.W. Knapp

NRCC Research Publication RR 94-1

The British Meteorological Office Rainfall and Evaporation Calculation System (MORECS) is modified to provide operational estimates of evaporation and soil moisture under several vegetation types in the northeastern United States. Although there are many models currently available to predict soil moisture deficits, most are crop-specific and therefore are unsuitable for the variety of vegetation types and crops in the Northeast.

MORECS is based on a variation of the Penman-Monteith Equation and uses solar radiation, air temperature, vapor pressure, and wind speed to estimate both potential and actual evapotranspiration. Numerous changes are made to the original MORECS model to adapt it for operational use in the Northeast. Among the more extensive modifications are the use of measured rather than modeled shortwave radiation; a revised calculation scheme for longwave radiation loss; and changes in phenological and crop parameters.

Evaporation and soil moisture observations and coincident climatological observations from several sites in the Northeast are used to evaluate the model's performance. For pan evaporation, the mean difference between the model and observations at 4 northeastern U.S. sites was 0.00 inches. For grass and bare soil, the model estimates averaged 0.06 inches less than corresponding soil moisture observations. A similar bias was noted for deciduous trees.

11 pp.

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