TITLE:
Spectral Crop Coefficient Approach for Estimating Daily Crop Water Use
AUTHORS:
Nithya Rajan, Stephan J. Maas
KEYWORDS:
Crop Coefficient, Evapotranspiration, Water Use, Ground Cover, Remote Sensing
JOURNAL NAME:
Advances in Remote Sensing,
Vol.3 No.3,
September
30,
2014
ABSTRACT: While the amount of water
used by a crop can be measured using lysimeters or eddy covariance systems, it
is more common to estimate this quantity based on weather data and crop-related
factors. Among these approaches, the standard crop coefficient method has
gained widespread use. A limitation of the standard crop coefficient approach
is that it applies to “standard conditions” that are invariant from field to
field. In this article, we describe a method for estimating daily crop water
use (CWU) that is specific to individual fields. This method, the “spectral
crop coefficient” approach, utilizes a crop coefficient numerically equivalent
to the crop ground cover observed in a field using remote sensing. This
“spectral crop coefficient” Ksp is
multiplied by potential evapotranspiration determined from standard weather
observations to estimate CWU. We present results from a study involving three
farmers' fields in the Texas High Plains in which CWU estimated using the Ksp approach is compared to observed
values obtained from eddy covariance measurements. Statistical analysis of the
results suggests that the Ksp approach
can produce reasonably accurate estimates of daily CWU under a variety of
irrigation strategies from fully irrigated to dryland. These results suggest
that the Kspapproach could be effectively used in applications such
as operational irrigation scheduling, where its field-specific nature could minimize
over-irrigation and support water conservation.