DWR_2807910

• Title: STATE AND DIVISION ENGINEER'S FORUM ENGINEERING ASSUMPTIONS - ATTACHMENT: CROP COEFFICIENT MEMO
• Author/Source: DEAN SANTISTEVAN, P.E.
• Author/Source: DIVISION OF WATER RESOURCES
• Keywords: CROP COEFFICIENT, CROP GROWTH
• Document Type - Reference Library: Presentations
• Document Date: 4/15/2014
• Year: 2014
• Team/Office: Division 1 Office

MEMORANDUM
December 13, 2013
Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney
Page 26 of 34

Small Grain. The Task Memo 59.1 crop curve for
estimate consumptive use. Findings from our study of ARS 1275 suggest the same. The coefficients
from Task Memo 59.1 present an unusual shape
shaped. It is interesting to note that the data from ARS 1275 suggests that the peak of the SCS TR
curve should be wider and the top of the
explain the peak in the Task Memo 59.1 curve that occurs in May. The difference may have less to do
with temperatures during the shoulder months and more with the development of the SCS curve itself.

Figure 26 – Comparison of crop curves for small grain

Overall, a trend relative to calibrations during the shoulder months was observed. In our analysis, the
growing season for sugar beets & corn
& sorghum was modeled to being in June
the calibrated curves did not show the high spikes during the growing season.

On the other hand, pasture grass
shoulder months and, coincidentally
support the presumption that high daytime temperatures and low night temperatures
months result in the greatest difference
the ASCE equation.

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Issues with Selecting an Appropriate Crop Growth Stage Coefficient for the SCS Mod. Blaney-Criddle Eqn.
The Task Memo 59.1 crop curve for small grains suggests that SCS TR
estimate consumptive use. Findings from our study of ARS 1275 suggest the same. The coefficients
from Task Memo 59.1 present an unusual shape early in the season, although one that is somewhat bell
It is interesting to note that the data from ARS 1275 suggests that the peak of the SCS TR
curve should be wider and the top of the kc curve should be reached earlier in the season. This may
sk Memo 59.1 curve that occurs in May. The difference may have less to do
with temperatures during the shoulder months and more with the development of the SCS curve itself.
crop curves for small grain
relative to calibrations during the shoulder months was observed. In our analysis, the
& corn was modeled to begin in May while the growing season for
in June. These crops tended to not include the shoulder months and
the calibrated curves did not show the high spikes during the growing season.
asture grasses, alfalfa, and small grains were all modeled to
coincidentally, the curve is exaggerated curve during the spring and fall
h daytime temperatures and low night temperatures during the shoulder
result in the greatest difference of ET when calculated with the Blaney-Criddle and
40 60 80
Percent of Growing Season
SCS TR-21, small grains
Task Memo 59.1
Average of ARS 1275
Criddle Eqn.
suggests that SCS TR-21 will under-
estimate consumptive use. Findings from our study of ARS 1275 suggest the same. The coefficients
one that is somewhat bell
It is interesting to note that the data from ARS 1275 suggests that the peak of the SCS TR-21
curve should be reached earlier in the season. This may
sk Memo 59.1 curve that occurs in May. The difference may have less to do
with temperatures during the shoulder months and more with the development of the SCS curve itself.

relative to calibrations during the shoulder months was observed. In our analysis, the
the growing season for beans
include the shoulder months and
were all modeled to grow during the
the spring and fall. This could
during the shoulder
Criddle and compared to
100