Sensitivity of the food and agriculture organization Penman-Monteith evapotranspiration estimates to alternative procedures for estimation of parameters

Lakshman Nandagiri, Gicy M. Kovoor

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Reference crop evapotranspiration (ET o) is a key variable in procedures established for estimating evapotranspiration rates of agriculture crops. As per internationally accepted procedures outlined in the United Nations Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 (FAO-56), using the Penman-Monteith (PM) combination equation is the recommended approach to computing ET o from ground-based climatological observations. Applying of the PM equation requires converting input climate and site data into a number of parameters, and FAO-56 recommends exact procedures for estimating these parameters. However, a plethora of alternative procedures for estimating parameters exist in literature. As a consequence, it is likely that ambiguous results may be obtained from the FAO-56 PM equation because of the adoption of such alternative (nonrecommended) supporting equations. The purpose of the present study is to evaluate differences that could arise in FAO-56 ET o estimates if nonrecommended equations are used to compute the parameters. Using historical climate records from 1973 to 1992 of a station located in the humid tropical region of Karnataka State, India, monthly ET o, estimates computed by FAO-56 recommended procedures were statistically compared with those obtained by introducing alternative procedures for estimating parameters. In all, 13 alternative algorithms for ET o estimation were formulated, involving modified procedures for parameters associated with weighting factors, net radiation, and vapor-pressure-deficit terms of the PM equation. For the 240-month period considered, nine of these algorithms yielded ET o estimates that were in close correspondence with FAO-56 estimates as indicated by mean absolute relative difference (AMEAN) values within 1% and maximum absolute relative difference (MAXE) values within 2%. The remaining four algorithms, involving nonrecommended procedures for the vapor-pressure-deficit and net-radiation parameters, yielded considerably different ET o estimates, giving rise to AMEAN values in the range of 2 to 8% and MAXE values ranging between 8 and 28%. The results of this study highlight the need for strict adherence to recommended procedures, especially for estimating of vapor-pressure-deficit and net-radiation parameters if consistent results are to be obtained by the FAO-56 approach. Journal of Irrigation and Drainage Engineering

Original languageEnglish
Pages (from-to)238-248
Number of pages11
JournalJournal of Irrigation and Drainage Engineering
Volume131
Issue number3
DOIs
Publication statusPublished - 01-05-2005

Fingerprint

Food and Agriculture Organization
Evapotranspiration
Agriculture
Food and Agricultural Organization
evapotranspiration
Organizations
agriculture
Food
food
Penman-Monteith equation
Vapor Pressure
net radiation
vapor pressure
Vapor pressure
irrigation and drainage
Irrigation
Radiation
Drainage
Crops
Climate

All Science Journal Classification (ASJC) codes

  • Agricultural and Biological Sciences (miscellaneous)
  • Water Science and Technology
  • Civil and Structural Engineering

Cite this

@article{9add765a408044e9b435d9537fcaa48a,
title = "Sensitivity of the food and agriculture organization Penman-Monteith evapotranspiration estimates to alternative procedures for estimation of parameters",
abstract = "Reference crop evapotranspiration (ET o) is a key variable in procedures established for estimating evapotranspiration rates of agriculture crops. As per internationally accepted procedures outlined in the United Nations Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 (FAO-56), using the Penman-Monteith (PM) combination equation is the recommended approach to computing ET o from ground-based climatological observations. Applying of the PM equation requires converting input climate and site data into a number of parameters, and FAO-56 recommends exact procedures for estimating these parameters. However, a plethora of alternative procedures for estimating parameters exist in literature. As a consequence, it is likely that ambiguous results may be obtained from the FAO-56 PM equation because of the adoption of such alternative (nonrecommended) supporting equations. The purpose of the present study is to evaluate differences that could arise in FAO-56 ET o estimates if nonrecommended equations are used to compute the parameters. Using historical climate records from 1973 to 1992 of a station located in the humid tropical region of Karnataka State, India, monthly ET o, estimates computed by FAO-56 recommended procedures were statistically compared with those obtained by introducing alternative procedures for estimating parameters. In all, 13 alternative algorithms for ET o estimation were formulated, involving modified procedures for parameters associated with weighting factors, net radiation, and vapor-pressure-deficit terms of the PM equation. For the 240-month period considered, nine of these algorithms yielded ET o estimates that were in close correspondence with FAO-56 estimates as indicated by mean absolute relative difference (AMEAN) values within 1{\%} and maximum absolute relative difference (MAXE) values within 2{\%}. The remaining four algorithms, involving nonrecommended procedures for the vapor-pressure-deficit and net-radiation parameters, yielded considerably different ET o estimates, giving rise to AMEAN values in the range of 2 to 8{\%} and MAXE values ranging between 8 and 28{\%}. The results of this study highlight the need for strict adherence to recommended procedures, especially for estimating of vapor-pressure-deficit and net-radiation parameters if consistent results are to be obtained by the FAO-56 approach. Journal of Irrigation and Drainage Engineering",
author = "Lakshman Nandagiri and Kovoor, {Gicy M.}",
year = "2005",
month = "5",
day = "1",
doi = "10.1061/(ASCE)0733-9437(2005)131:3(238)",
language = "English",
volume = "131",
pages = "238--248",
journal = "Journal of Irrigation and Drainage Engineering - ASCE",
issn = "0733-9437",
publisher = "American Society of Civil Engineers (ASCE)",
number = "3",

}

TY - JOUR

T1 - Sensitivity of the food and agriculture organization Penman-Monteith evapotranspiration estimates to alternative procedures for estimation of parameters

AU - Nandagiri, Lakshman

AU - Kovoor, Gicy M.

PY - 2005/5/1

Y1 - 2005/5/1

N2 - Reference crop evapotranspiration (ET o) is a key variable in procedures established for estimating evapotranspiration rates of agriculture crops. As per internationally accepted procedures outlined in the United Nations Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 (FAO-56), using the Penman-Monteith (PM) combination equation is the recommended approach to computing ET o from ground-based climatological observations. Applying of the PM equation requires converting input climate and site data into a number of parameters, and FAO-56 recommends exact procedures for estimating these parameters. However, a plethora of alternative procedures for estimating parameters exist in literature. As a consequence, it is likely that ambiguous results may be obtained from the FAO-56 PM equation because of the adoption of such alternative (nonrecommended) supporting equations. The purpose of the present study is to evaluate differences that could arise in FAO-56 ET o estimates if nonrecommended equations are used to compute the parameters. Using historical climate records from 1973 to 1992 of a station located in the humid tropical region of Karnataka State, India, monthly ET o, estimates computed by FAO-56 recommended procedures were statistically compared with those obtained by introducing alternative procedures for estimating parameters. In all, 13 alternative algorithms for ET o estimation were formulated, involving modified procedures for parameters associated with weighting factors, net radiation, and vapor-pressure-deficit terms of the PM equation. For the 240-month period considered, nine of these algorithms yielded ET o estimates that were in close correspondence with FAO-56 estimates as indicated by mean absolute relative difference (AMEAN) values within 1% and maximum absolute relative difference (MAXE) values within 2%. The remaining four algorithms, involving nonrecommended procedures for the vapor-pressure-deficit and net-radiation parameters, yielded considerably different ET o estimates, giving rise to AMEAN values in the range of 2 to 8% and MAXE values ranging between 8 and 28%. The results of this study highlight the need for strict adherence to recommended procedures, especially for estimating of vapor-pressure-deficit and net-radiation parameters if consistent results are to be obtained by the FAO-56 approach. Journal of Irrigation and Drainage Engineering

AB - Reference crop evapotranspiration (ET o) is a key variable in procedures established for estimating evapotranspiration rates of agriculture crops. As per internationally accepted procedures outlined in the United Nations Food and Agriculture Organization's Irrigation and Drainage Paper No. 56 (FAO-56), using the Penman-Monteith (PM) combination equation is the recommended approach to computing ET o from ground-based climatological observations. Applying of the PM equation requires converting input climate and site data into a number of parameters, and FAO-56 recommends exact procedures for estimating these parameters. However, a plethora of alternative procedures for estimating parameters exist in literature. As a consequence, it is likely that ambiguous results may be obtained from the FAO-56 PM equation because of the adoption of such alternative (nonrecommended) supporting equations. The purpose of the present study is to evaluate differences that could arise in FAO-56 ET o estimates if nonrecommended equations are used to compute the parameters. Using historical climate records from 1973 to 1992 of a station located in the humid tropical region of Karnataka State, India, monthly ET o, estimates computed by FAO-56 recommended procedures were statistically compared with those obtained by introducing alternative procedures for estimating parameters. In all, 13 alternative algorithms for ET o estimation were formulated, involving modified procedures for parameters associated with weighting factors, net radiation, and vapor-pressure-deficit terms of the PM equation. For the 240-month period considered, nine of these algorithms yielded ET o estimates that were in close correspondence with FAO-56 estimates as indicated by mean absolute relative difference (AMEAN) values within 1% and maximum absolute relative difference (MAXE) values within 2%. The remaining four algorithms, involving nonrecommended procedures for the vapor-pressure-deficit and net-radiation parameters, yielded considerably different ET o estimates, giving rise to AMEAN values in the range of 2 to 8% and MAXE values ranging between 8 and 28%. The results of this study highlight the need for strict adherence to recommended procedures, especially for estimating of vapor-pressure-deficit and net-radiation parameters if consistent results are to be obtained by the FAO-56 approach. Journal of Irrigation and Drainage Engineering

UR - http://www.scopus.com/inward/record.url?scp=20844460344&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=20844460344&partnerID=8YFLogxK

U2 - 10.1061/(ASCE)0733-9437(2005)131:3(238)

DO - 10.1061/(ASCE)0733-9437(2005)131:3(238)

M3 - Article

AN - SCOPUS:20844460344

VL - 131

SP - 238

EP - 248

JO - Journal of Irrigation and Drainage Engineering - ASCE

JF - Journal of Irrigation and Drainage Engineering - ASCE

SN - 0733-9437

IS - 3

ER -