HISTORICAL EVOLUTION OF ET

Transcription

1 HISTORICAL EVOLUTION OF ET ESTIMATING METHODS A Century of Progress by Marvin E. Jensen 12 Mar 2010 ARS/CSU ET Workshop 1

2 INTRODUCTION This a partial condensation of a previous paper: Jensen & Allen (2000), 2000 ASAE National Irrig. Symposium it includes developments since 2000 In this paper, I also place more emphasis on my involvement reviewing old docs, early est methods, and current literature added pictures of key personnel methods based on theory and European methods dissemination and adoption of new U.S. estimating methods new models based on satellite imagery (SEBAL and METRIC) development of the ASCE Manual 70, FAO 56, the ASCE Standardized Reference ET Equation, and the 2 nd edition of ASCE Manual Mar 2010 ARS/CSU ET Workshop 2

3 EARLY ESTIMATING METHODS Early need for ET estimates Early estimating methods initially, estimates were only for seasonal estimates then estimates were made for monthly periods Mean air temperature was the primary weather variable, or temperature above 32 F Secondary variables were: relative humidity percent of daylight hours 12 Mar 2010 ARS/CSU ET Workshop 3

4 EARLY IRRIGATION STUDIES Irrigationdevelopment began the mid 1800s deliveries to farms varied widely and exceeded CU over irrigation wasthe first and most serious mistake made by early settlers (Buffam, 1892) Irrigation investigations began around 1900 Duty of Water measurements were made involving water delivered to canals and water delivered to farms units were acres per 1 cfs, or depth applied 12 Mar 2010 ARS/CSU ET Workshop 4

5 RESULTS OF MY EARLY WORK My involvement began in1960 monthly k values From about 100 values for full crop cover, ET p = ( T 0.37) R s approximated ET from a crop like alfalfa 1962 preliminary report, estimating ET from R s Publication Jensen and Haise (1963), objective encourage engineers, soil scientists and agronomists to begin thinking about solar energy as a primary variable in estimating ET (and to motivate) rather than only air temp 12 Mar 2010 ARS/CSU ET Workshop 5

6 EARLY WATER USE STUDIES 1897Joint USDA Exp. Stn investigations started and continued under various departments investigations were transferred to SCS in measurements of Duty of water acres that could be irrigated with a constant flow ordepth ofwater applied at the farm turnout, it was called net duty of water Progress report, ASCE Duty of Water committee presented in 1927 by O.W. Israelson published in 1930 (Anonymous, 1930) 12 Mar 2010 ARS/CSU ET Workshop 6

7 EARLY TRANSPIRATION STUDIES 1902 USDABur Bur. ofplantindustryestablished Briggs, biophysicist, and Shantz, plant physiologist, conducted classicstudies studies in eastern Colorado from 1913 to 1916 they recognized dthat t solar radiation was the primary cause of cyclic changes in environmental factors developed hourly equations of T as a function of R s and temperature rise; and R s and VP deficit 12 Mar 2010 ARS/CSU ET Workshop 7

8 EARLY ESTIMATING METHODS 1924 Hedke proposed p a method based on heat available defined as degree days (temp x days) 1942 Blaney and Morin proposed a method based on meantemperature temperature, daylight hours and humidity 1942 Lowry and Johnson proposed a method based on maximum temperature above 32F 1948 Thornthwaite proposed a method based on mean monthly temperature. He recognized its limitations such as why PET at a given temperature is not the same everywhere 12 Mar 2010 ARS/CSU ET Workshop 8

9 Blaney Criddle Method Mostwidely known method (1945, 1950, 1952, 1962) up to the 1970s U = KF = kf k monthly CU coefficient based on temperature f = t p/100 where t = mean monthly temperature, t F, and p = mean monthly percent of annual daytime hours 12 Mar 2010 ARS/CSU ET Workshop 9

10 Harry F Blaney 1966 Receiving ASAE John Deere Medal dl 12 Mar 2010 ARS/CSU ET Workshop 10

11 ICID Vice President Mar 2010 ARS/CSU ET Workshop 11

12 Why Not R a instead of %DL? %DL/%DL(max) and Ra/Ra(max) degrees N Lat Ra % DL 12 Mar 2010 ARS/CSU ET Workshop 12

13 deg N Lat Ra % DL deg N Lat Ra % DL 12 Mar 2010 ARS/CSU ET Workshop 13

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16 Transition Methods in the U.S. Temperature and solar radiation Jensen Haise (1963) ET alfalfa ref = (T f 0.37) R s (Western USA) Stephens and Steward (1963) ET grass ref = (T f 0.19) R s (Florida) Hargeaves and Samani (1985); Hargreaves et al. (1985) ET grassref = TD 0.5 (T c ) R a 12 Mar 2010 ARS/CSU ET Workshop 16

17 Methods Based on Theory The Bowen Ratio, BR (Bowen, 1926) (BR = ΔT/Δe ) Was used for estimate evaporation from water in the 1930s, but was not used to estimate ET from land until Penman (1948) Penman applied physics and [ET = (R n G)/(1 + BR)] the Bowen Ratio, energy balance along with the the rates of sensible heat and vapor transfer Penman laid the foundation for later development of improved estimating methods (Penman, 1948, 1956, and 1963) Surface resistance was addedto the Penman equation (Penman and Long 1960; Monteith 1965; & Rijtema 1965) Today, ET measurement methods include eddy covariance, boundary layer theory, remote sensing and energy balance or a combination of these methods 12 Mar 2010 ARS/CSU ET Workshop 17

18 Penman Equation (1948) E = (Δ R n + γ λ E a )/(Δ + γ) (Eq. 16) E = evaporation Δ = the slope of saturated vapor pressure curve γ = psychrometric constant R n = net radiation at crop surface λ = latent heat of vaporization E a was an empirical wind function (like Rohwer s (1931) equation 12 Mar 2010 ARS/CSU ET Workshop 18

19 Howard L Penman Pres., Royal Meteor. Soc Mar 2010 ARS/CSU ET Workshop 19

20 John L Monteith Pres., Royal Meteor. Soc Mar 2010 ARS/CSU ET Workshop 20

21 Other Estimating Methods The European uopea engineers ee sprogressed more oerapidly Makkink (1957) developed a formula for potential ET based on solar radiation & air temp Turc (1960, 61) developed a formula based on 10 day mean air temperature and solar radiation Rijtema (1958) a formula for individual crops using crop factors and length of growing season Olivier (1961), a formula for monthly CU using wet bulb depression and clear sky radiation factors Jensen (1968) proposed estimating ET using alfalfa ref x K c known as the two step process 12 Mar 2010 ARS/CSU ET Workshop 21

22 Some details of my involvement USDA SCS SCS Request to ARS USDA calculate crop coefficients for the B C formula Howard Haise and Harry Blaney solicited data from ARS researchers the calculated monthly coefficients varied widely I prepared a new questionnaire i basic soil water and climate data were requested criteria were established for screening the data new calculations, resulted in ~1000 ET rates for short time periods along with estimated solar radiation 12 Mar 2010 ARS/CSU ET Workshop 22

23 RESULTS From about 100 values of ET for full crop cover ET = (0.014 T 0.37) R s approximated ET from a crop with full cover like alfalfa with 30 to 50 cm ( in.) of growth A 1962 preliminary report, estimating ET from R s, prepared p for a workshop on estimating ET Publication by Jensen and Haise (1963) had as its objective to encourage (& motivate) engineers soil scientists and agronomiststo to consider solar energy as the primary variable controlling ET 12 Mar 2010 ARS/CSU ET Workshop 23

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25 Adopting & Disseminating New Estimating Methods Though g the physicist still has some problems he can solve by himself, much of his future contribution to understanding evaporation in agriculture must be in collaboration with the biologist and soil scientists (Penman, 1956) In 1966 we organized a conference of ET specialists in Chicago In 1966, I was also asked to chair the ASCE committee on Water Requirements New members were added to the ASCE WR committee Control members were Burman, U of Wyo; Collins, SCS; Gibbs, USBR; and Johnson, USGS Harry Blaney remained on the committee 12 Mar 2010 ARS/CSU ET Workshop 25

26 Dissemination Continued An ASCE report on CU was prepared p in 1973, it was widely distributed (Jensen ed. 1974) and was the start of ASCE Manual 70 (Jensen et al. 1990) I lftth left the committee for three years while serving on the ASCE I&D executive committee Committeemembers members continued work onthe manual In 1986 an ASCE Manual subcommittee was formed consisting of Allen, Burman, Blatchley, Jensen (chm), Johns, Stone and Wright, eventually resulting in the ASCE Manual 70 Evapotranspiration and Irrigation Water Requirements (Jensen et al. 1990) 12 Mar 2010 ARS/CSU ET Workshop 26

27 Dissemination Continued RickAllen published a detailed paper in the Agronomy Journal (Allen et al. 1989) FAO organized a consultation for revising FAO 24 Crop Water Requirements with participants from seven countries (Smith et al. 1991) (Allen, Jensen and Pruitt represented the U.S.) Draft copies of ASCE Manual 70 was a key reference at this 1990 conference 12 Mar 2010 ARS/CSU ET Workshop 27

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33 SATELLITE IMAGERY IMAGERY MODELS In thenetherlands Netherlands, the surface energy balance model for land was developed by Bastiaanssen et al. in 1998 (SEBAL) In the U.S., a model was developed by Allen et al. (2007) using some of the basic principles in SEBAL, called a model for Mapping Evapotranspiration at high Resolution using Internalized Calibration (METRIC) 12 Mar 2010 ARS/CSU ET Workshop 33

34 Reference Crop x Crop Coefficient Known as the etwo step method widely used Was proposed in 1968 with alfalfa as the ref crop Crop coefficient Similar to that proposed by Wijk and de Vries (1954) Results can be very robust requires judgment in selecting and applying crop coefficients Example: Comparison with SEBAL for IID for water year 1998, +2% all areas to +5% agr. land (Jensen & Walter 2002) 12 Mar 2010 ARS/CSU ET Workshop 34

35 Recent Methods The Irrigation Association requested the ASCE ET Committee to recommend a single procedure for est. reference ET in the U.S. An ASCE task committee developed such a procedure described in 2000 and published a report in 2005 (ASCE EWRI EWRI 2005) Remote sensing using satellite data (SEBAL and METRIC) Remote sensing used to estimate K c (grd, aircraft, satellite) procedures for estimating K c from ground cover and height expanded the FAO K c database (Allen and Pereira 2009) A one step estimating i method theory (Shuttleworth h 2006) was tested in Australia (Shuttleworth & Wallace 2009) Also known as Direct Penman Montheith method The 2 nd ed. of Manual 70 is nearing completion 12 Mar 2010 ARS/CSU ET Workshop 35

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37 SUMMARY AND CONCLUSIONS This brief presentation summarizes a century of progress in the development of modern methods of estimating seasonal, daily and hourly ET (Only two centuries ago Dalton first described the hydrologic cycle) Most of the progress in the U.S. was made during the last third of a century. ET is a complex process involving plants, soils, local weather such as wind speed and humidity, and solar and long wave radiation Many scientists and engineers were involved in the development of current, modern ET estimating technology My association with development process was a learning experience contacts with leading U.S & int l scientists and engineers was rewarding I have emphasized my involvement its been my work for the past 50 yrs I may have missed some recent developments I tried to highlight main items For a recent and more detailed review, see Farahani et al. (2007) (Photos follow, time permitting) i 12 Mar 2010 ARS/CSU ET Workshop 37

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