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Technical Note (National Research Council of Canada. Division of Building Research), 1955-03-01
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Soil Moisture at Winnipeg: 1947 to 1954 (A Preliminary Study)
Boyd, D. W.
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---DIVISION OF BUILDING RESEARCH 'I
NATIONAL RESEARCH COUNCIL OF CANADA
Ser
TH1 N278
no0 194
c. 2
ｾｽｦｦｌＮＬ
'1E
C
1HIN II CAlL
NOTJE
No.
194
NOT FOR PUBLICATION
PREPARED BY D.W. Boyd PREPARED FOR General Information CHECKED BY ANAL YZep:,
FOR INTERNAL USE
APPROVED BY
R.F.L.
March
1955
SUBJECT : Soil Moisture at Winnipeg:
1947
to 1954
(A Preliminary Study)
In
1948
C.W. Thornthwaite published formulae forcalculating from climatological data the approximate evaporation or transpiration from sailor vegetation. He assumed that most soils could store approximately the same amount of moisture
(10
cm. or4
inches) which would be available later for plant use. This is in addition to any moisture which is bound too closely to the soil particles to be available to plants. He also assumed that the moisture removed from the soil depended mainly on the air temperature and the length of daylight; and did not vary significantly with other meteorological elements or with the type of vegetation. In spite of these assumptions it is claimed that the formulae give quite satisfactory results.The daily mean temperatures at Winnipeg have been used, with tables based on Thornthwaite1s formulae, to obtain the daily evapotranspiration or depletion of soil moisture. This value and the daily total precipitation are used to find the soil moisture storage day by day. Additional precipitation after the
storage has reached
4
inches is called surplus and is assumed to run off. Potential evapotranspiration after the storage has reached zero is called deficit. It does not affect the storage, and is merely a measure of the moisture that could have been removed from the soil if there had been any there.In the following table the soil moisture ｳｴｯｲｾｧ･ in inches at the end of each month, and the total surplus or deficit for each month in inches per month, are given for the seven years from August
1947
to August1954.
All these values are plottedon the accompanying graph. One Value for each month is, of course, only a rough sample of the computed daily values of storage,
surplus and deficit.
Perhaps the most noticeable feature of the graph is the large surplus during the winter of
1949-50,
preceding the flood- 2 ...
in that area. The surplus in the following spring was quiDe small and in
1952
there was no surplus. The large surplus of over six inches in the spring of1953
must have been quite noticeable after the two t1dryll springs. Another remarkable feature about the surpluses in1953
and1954
shows up in the table: they were both quite late in the year compared with the previous five springs.The time of the large surpluses does vary a lot, however, as seen in the average surplus. In the case of the deficits, however, they seem to be fairly evenly grouped around August.
Surplus for the month in inches 1947 0 0 0 0 0 8 0 .02 .76 1.45 .49 0 0 0 0 0 0 0 9 .86 1.07 .69 0 0 0 0 0 0 1.07 1.04 1.59 1950 1.83 .69 .37 1.48 3.07 0 0 0 0 0 0 0 1 0 .03 .63 .40 0 0 0 0 0 0 0 0
e
2 0 0 0 0 0 0 0 0 0 0 0 04
0 0 .76 1.13 1.63 .63 1.90 0 0 0 0 0 0 0 0 1.69 .22 1.16 Aver. .38 .26 .46 .88 .77 .26 .27 0 0 .15 .15 .23Deficit for the month in inches
1947 .08 1_75 .22 0 0 8 0 0 0 0
