An Improvement in the BBH Model for Estimating Evapotranspiration from Cornfields in the Upper Yellow River

The bucket with a bottom hole (BBH) model of soil hydrology was improved to incorporate bioprocesses such as surface rainfall interception and macropore flow into it by introducing three model parameters or two composite parameters. The improved model (BBH-B model) was applied to the estimation of evapotranspiration (ET) from a cornfield in the upper Yellow River. The results obtained are summarized as follows. (a) Estimates of the cumulative ET during periods of about one month were made using the BBH-B model with fair accuracy if the model parameters could be evaluated appropriately. (b) ET had a large spatial variation within the cornfield. (c) The major zone of water use by corn moved downward through the soil as the growing season progressed. The ratio of root water uptake in depths between 40 cm and 100 cm to ET increased from about one-forth in June, when LAI increased quickly, to about one-half in September, when the corn maturred. (d) The surface conditions, such as the fraction of crop cover, exerted a large influence on the partition of rainwater at the surface of the cornfield.