Evaporation Measurements in Canada

(1)

Publisher’s version / Version de l'éditeur:

Technical Note (National Research Council of Canada. Division of Building Research), 1958-01-01

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20358828

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Evaporation Measurements in Canada Boyd, D. W.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=5944b12b-8c3b-4534-a53f-059d8743ba48 https://publications-cnrc.canada.ca/fra/voir/objet/?id=5944b12b-8c3b-4534-a53f-059d8743ba48

(2)

DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANA

NOTJE

'f

E

C

JHI

N II

C

AIL

NOT FOR PUBLICATION _FOR _INTERNAL _USE

PREPARED BY D.W.Boyd* CHECKED BY APPROVED BY NBH

ｇ･ｮ･ｾ｡ｬ Distribution'

PREPARED FO,R

DATE January

1958

SUBJECT ｅｶ｡ｰｯｾ｡ｴｩｯｮ Measurements in Canada

The amount of evaporation from tanks of water eXpoesd to the

ｷ･｡ｴｨ･ｾｨ｡ｳ been ｭ･｡ｳｵｾ･､ at a few stations in, ｃ｡ｮ｡､｡ｴｯｾ over ｴｨｩｾｴＷ

years •. 'At the present time over two dozen stations are taking these

observations. The sum of the evaporation

and

transpiration<of'water

from moist plots of ground has been measured at a few $tations during

the last ten years. Other methods of ｭ･｡ｳｵｾｩｮｧ the'''dry-lng'power"

of the air, such as the Piche atmometer and the Bellaniplate. 'have also been used in Canada, but few data have been published.

Open Evaporation Tanks

Metal ･ｶ｡ｰｯｾ｡ｴｩｯｮ tanks. are usually a few feet ｳｱｵ｡ｾ･ and one

ｯｾ two teet deep. Those used in Canada have usually been sunk in the

ｧｾｯｕＺｮ､ｷｩｴｨｩｮ｡ｮ inch or two of the rim. Th.e ｷ｡ｴ･ｾ level is measured

daily or oftener and the ､ｩｦｦ･ｾ･ｮ｣･ｳ taken as ｭ･｡ｳｵｾ･ｳ of the

･ｶ｡ｰｯｾ｡ｴｬｯｮＮ Rainfall, as measured by a nearby gauge. is allowed

ｲｯｾＬ and, when necessary, water is added to ｫｾ･ｰ the water level

within

a

few inches of the ｾｩｭＮ Middleton (1) gives a short

discus-sion of ･ｶ｡ｰｯｾ｡ｴｩｯｮ measurements and describes the evaporation tank

arid ｯｴｨ･ｾ instruments.

Robertson (2) has oollected the monthly totals 'of the tank evaporation measurements at Experimental Farms in Canada to the end

of 1952, and in an appendix he gives specifioations for a standard

ｾ evaporation tank.

ｾ

ｍｩｬｬ｡ｾ

(3) has developed the theory of evaporation from free

ｾｷ｡ｴ･ｲ surfaces and his equations show how the evaporation depends on

ｾＧｷｩｮ､ speed and on the dimension of the tank parallel to the wind

direction. Other properties of the tank that affeot the evaporation

C:>include: height of the rim above the water surface, depth (and hence

ｾｨ･｡ｴ storage capacity) of the water, surfaoe on which the tank rests

(wooden frame, or buried in ground, etc.), and, of oourse, the

Eo-

expo sure to wind and sunshine.

0---

_ｾＪ _{D.W. Boyd is a member of the staff of the Meteorological Division}

of the Department of Transport seconded to ｷｯｾｫ full time as

Climatologist with the Division of Building Research. This note

therefore represents a joint contribution from this Division, and from the Meteorological Division.

(3)

2 -Evapotranspirometers

Apparatus for the measurement ot evapotranspiration from .

plots

or

ground a rew feet square has been desoribed by Penman

(4),

Mather (5) and others. Descriptions of the installations at

Oanadian stations and tabulations of the measurements are given

in a series

or

papers by Sanderson

(6, 7, 8, 9).

Measurements

have been made at Toronto, Windsor, Guelph, Kapuskasing, and Norman Wells.

The measurement of evapotranspiration requires bulky

apparatus and the oarefu1 attention of

a

skilled ｰ･ｾｳｯｮ to yield

satisfaotory results. It has therefore beoome common to, calculate

the potential evapotranspiration from observations of other weather elements, instead of attempting to measure it directly.

Penman (4) developed a formula in whioh ｶ｡ｬｾ･ｳ of temperature,

sunshine, wind speed, and vapour pressure were used to yield a value

for the potential evapotranspiration. A much simpler (and probably

less acourate) formula using only temperature and length

ot

daylight

was developed by Tbornthwaite (10). Thornth aite's formulae were

originally developed as a means of classityingclimates, but they have been widely used to estimate soil moisture on a daily basis and hence to assess the need for irrigation or to predict runoff. Latent Evaporation

Robertson (11) uses the term "latent evaporation" for the

evaporation measured by the b1aok Bellan! plate atmometer. This is

a relatively inexpensive instrument whioh Robertson says appears to react to the influence of sunshine, wind, temperature, and·vapour

pressure in muoh -the same way as a crop'. For the agriculturalist

ｯｲｴｾ･ｩｲｲｩｧ｡ｴｩｯｮ engineer it would appear to be an ideal instrument. At present however, the only Oanadian data published seem to'be odd months used as examples in papers by Robertson and Holmes (12). Other Evaporimeters

An

evaporation pan with a rain shield has been in operation

at the Experimental Farm in Summerland, B.O. for some time, and the

Experimental Farm at Regina is ｵｳｾｮｧ a PIche evaporimeter in ｾ､､ｩｴｩｯｄ

to a tank. Readings from these instruments are on file at the

Meteorological Office in Toronto. Discussion

It has been pointed out by Hare (13) that the problems

presented by evaporation Measurements are of two kinds: firstly,

a clear definition of evaporation as a ｯｬｩｾｴＱ｣ element, and, secondly,

the instrumental measurement of the element seleoted. The question

of definition is the more difficult but must be answered first.

(4)

.. 3

-Hare goes on to say: "Evaporation is normally thought of

as being divisible into evaporation off water-bodies and

evapo-transpiration otf plant-covered soil. Since the former is the

simpler prooess, it is often suggested that evaporation off 'an , open-water surface' should serve as a standardized measure of

atmosphere 'evaporating power', a parameter tormerely adopted by

Penman. In tact, however, evaporation off standardized evaporating

'pans gives a poor theoretioal estimate of evaporating power beoaus

, c;>f, (1·) the rim-turbulenoe, (2) the internal oonvection, ｾｮ､ (3) the

radiative absorption by the oontaining a1ls. Pans 'give useful

,oomparative figures, but no absolute measure of a natural prooess.

What,. in any oase, does one mean by an open-water sur.faoe' Ideally,

ｯｾ･ means a unit area of an infinite evaporating ｳｵｲｦ｡｣ｾＬ unattainable

in practice because of wave- and spray-development. Henoe it. seems

'unlikely to the author that pan or any other open- ater surface

measurements will give an adequate standard. If, ｨｯｷ･ｶ･ｲｾ QDe uses

instead the evaporation off a plant-covered so11, one must again

｡､ｭｬｾｾｨ･ difficulties ot standardization: day-length, soil moisture ,content, the effects of the surfaoe and the roughness of the crown

laye'r must all be oontrolled it one is to measure atmosphere evaporating power •

.·.":Since evaporation thus eludes direct' observation ons .,ri'gorousbasis·, and since it is a Vital element in both physioal

cl,.1matology and synoptio meteorology (though few synoptioians·· .

ｲｾ｡ＱＱｺ･Ｇ .,this) ,alternative measures must be found ＬＭＭ｡ｬＱｴＱｯｳｴ｣･ｲｴｾｩｮｬＧＱ

ＱｮｴｬＱ･Ｚｲｾ｡ｬｭ of derived parameters, in which the e-o-aporation

1S

. , .. . . It '

ｲｩｮｦＧｾｲｲ･､Ｌ not measured.

The use of derived parameters as Hare suggests may solve ,theseoond problem but it does not obviate the necessity of defining

evaporation as a climatic element. Some sort of standard surfaoe

and standard wetness must be agreed upon. Robertson has a possible

answer in the black Ballani plate, but at present it is not widely used.

The standard evaporimeter in the United States ｗ･ｾｴ｢･ｲ Bureau

is a four foot oiroular tank, ten inches deep and resting just above

ground level on a wooden framework (l1.,.). It seems that the Canadian

Meteorological Servioe favours the same instrument as a standard tor Canada'.

(5)

/ '

4 -e

REFERENCES

(1) Middleton W.E.K. Meteorological instruments. .Second edition,

University ot Toronto Press,. Toronto

1943-(2) Robertson, G.W. Evaporation measurements at branch units-ot the

Experimental Farms Servioe throughout. Canada. Bull. Div. of

Field Husbandry, Soils and Agric. Engin., Exp.Farms Serve

19 p.

1953-(3) Millar, F.G. Evaporation trom tree water surtaces.,Cabad:f:an.

, Meteorologioal Memoirs No.2. p. 43-65.1937.' '.

(4) penman, H.L. Natural evaporation !'rom open water, ｢｡Ｚｲｾ .so11 and

. grass. Froc. Roy. Soo. London 1948. Sere !, 193,120-145.

(5) Mather, John R. A SUDmlm-y ot evapotranspiration at ｓ･｡ｾｲｯｯｫＬ

New 'Jersey. The Johns Hopkins Univ., Lab. of Climatology.

Publications in Climatology, Vol. 7, No. 1,Seabroc>k, N.J.

p. 7...28. 1954. . '. .... . . .

(6) Sanderson, Marie. An experiment to measure ｾｯｴ･ｮｴｩ｡ｬ

evapptranspiration. Can. Jour. Research, C, Vol. 26, \

p. 445-454. 1948.

!. . Ｌｾ

(7) Sanderson, Marie. Three years ot evapotranspiration at Toronto.

Can. Jour. Researoh, 0, Vol. 28, No.1. p. 482-492,. ()ct. 1950.

(8) Sanderson, Marie •. Measuring potential evapotranspiration at

. Norman Wells, 1949. Geographical Review, Vol. 40, No.4,

p. 636-645, Oct. 1950. . ..

(9) Sanderson, Marie. Observations of potential evapotranspiration

at Windsor, Ontario, 1953. Johns Hopkins Univ., Lab. of

Climatology, Publications in Climatology, Vol.

7,

No.1.

Seabrook, N.J. p. 91-93. 1954. . . .

(10) Thornthwaite, O.W. An approaoh toward a rational c1assitication

ｯｴ｣ｾｩｭ｡ｴ･Ｎ Geog. Rev., Vol. 38, (1), Jan. 1946. p. 55-94.

(11) Robertson,. G.W. Latent evaporation: its oonoept, measurement

and app1ication. Prooessed paper. Field Husbandry, Soils

and Agrio. Eng •. Div., Central ｅｸｰ･ｲｩｭ･ｮｾ｡ｬ Farm Servioe

Ottawa 1954.

(12 ) Robertson, G.W. and R.M. Holmes. Estimating irrigation water

requirements from meteorologioal data. Div. of Field

Husbandry, Soils and Agric. Eng., Central Experimental

Farm, Ottawa 1956. .

(13) Hare, F.K. Some notes on evaporation. World Met. Organization.

Comm. tar Climatology, Seoond Session, Washington, January 1957, Doc. 67 Annex.

(6)

5

-(14)

u.s.

Dept. of Commettce. Instttuotions tor climatologioal observ8tts.

Weathett Butteau. Cittc. B., lOth ed. (Evapottstion: p. 33-41)

Ootober 1955.

ADDITIONAL PAPERS CONCERNED WITH EVAPORATION IN CANADA OR WITH THE MEASUREMENT OF EVAPORATION

Berry, W.M. and W. Stiokling. Evaporation from lakes and

reservoirs in the northern plains region in North Amettioa. Internat. Assoc. of Geodesy and Geoph., Surface Water Comm.,

Rome, General Assembly, Vol. 3, p. 121-134. 1954.

,Blaney, R.F. and K.V. Morin. Evaporation and oonsumptive use

, ot watett tormulae. Pt. 1. Trans. Amer.Geoph. Union, ' .

p. 16-83, 1942.

;}

'BUll, Howard W. Evapo-transpiratlon:excerpts trom seleoted

references. New Orleans, Aug. 1953.117p. US Southern

Forest Exp. Stn. 000asiona1 paperNo. 131. '

Canada, Dept. ot Agrioulture. Evapottation fttom lakes and reservoirs

on the Canadian Prairies. Prairie Farm Rehab. Admin., HydrologJ'

Div., Prairie Provinces Water Board Report NOe

5,

48p. 1952. '

Garnier, B.J. A simple apparatus for measuring potential

, evapotranspiration. Nature, Vol. ＱＷＰｾ No. 4320, 16 August

1952.

Garnier, B.J. and W.V. Lewis. Potential evapotttanspiration:

, An appeal for its measurement. Weather, Vol. 9, No.8,

Aug. 1954, p. 243-245. Disoussion in Letter to the Editor I

by J.B. Rigg in Weather, Vol. 10, No.1, Jan.l955, p. 31-32.

Gilbert, M.J. and C.H.M. Van Bavel. A simple field installation

for measuring maximum evapotranspiration. Trans. Amer. Geoph.

Union Vol. 35, No.6, Dec. 1954, p. 937-942.

Holmes, R.M. and G.W. Robertson. Conversion of latent

evaporation to potential evapotttanspiration (to be published).

Owens, J.S. An instrument for measuring evapottation trom

surtaoes. Jour. ot Scientific Instruments. Vol. 12, No.9,

Sept. 1935, p. 291.

Penman, B.L. The dependence ot transpiration on weather and

soil conditions. JoUItnal of Soil Science, Vol. 1, No.1,

p. 74-89, 1949

(7)

6

-Perry, P.C. Preoipitation-evaporation relationship tor the

Canadian Prairie. Engineering Jour., Vol. 32, No.8,

p. 468-473. Aug. 1949.

...

Sanderson, Marie. Is Canada's Northwest SubhWn1c:lTCanadian

Gaog. Jour. Vol.

41,

No.3. p.142-146. Sep1;ember 1950.

Sanderson, Marie •. The measurement ot evapoz-ation'ln Canada.

. . Internat.Union ot Geodesy and Geoph., Internat. Assoo. ot

Hydrology. Brussels Gen. Assemb1,.,p. 474-479.·1951.

Sanderson, Marie. The status ot evaporation studies 1n Canada.

Report to Commission on Potamo10gy,·Paper No. 20 (n.d.)

Stanhi11, G. Evaporation of water trom soil under field

oonditions. Nature, ｖｯＱｾ 116, No. 4411. JulY' 9, 1955,

p. 82-83.

,u.s.

Dept. ot Agriculture. Water. The Y'earbook of agriculture 1955.

V8n Wijk, W.R. and D.A. DeVries. Evapotranspiration. Netherlands

J. Agric. Scl., Vol. 2, No.2, p. 105-119. ＱＹｾＮ

VelhmeY'er, F.J. and F.A. Brooks. Measurements of cumulative

evaporation trom bare soil. Trans. Amer. Geoph. Unlon.

Vol. 3$,

No.4,

August 1954, p. 601-607. . '

Veihmeyer,F.J. and A.H. Hendrickson. Does transpiration

deorease 8sthe soil moisture deoreases? Trans. Amer. Geoph.

·Union., Vol. 36, No.3, p. 425-448, June 1955•.