The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal
Autor(a) principal: | |
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Data de Publicação: | 2008 |
Outros Autores: | , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
Texto Completo: | http://hdl.handle.net/10400.5/6000 |
Resumo: | We studied the seasonal and interannual variation in surface energy fluxes – net radiation (Rn), soil heat (G), sensible heat (H) and latent heat (lE) fluxes – and water vapour exchange above a Mediterranean C3/C4 grassland in Portugal, during two hydrological years, i.e., the period from 1 October to 30 September of the next year, of contrasting rainfall. The first year, 2004–2005, was dry, with total precipitation 45% below the long-term mean (669 mm), whereas the following, 2005–2006, was normal, with total precipitation only 12% above the long-term mean. Soil water availability and plant canopy growth were the most important factors in determining the seasonal and interannual variation in energy partitioning. During autumn, winter and early spring the ratio lE/Rn dominated over H/Rn, in the two years of the study, whereas on an annual basis, the major portion of Rn was consumed in H and lE in the dry and normal years, respectively. The total annual evapotranspiration (E) and its daily maximum were 316 mmand 2.8 mmper day, respectively, for the dry year, and 481mmand 4.5 mmper day for the normal year. After the senescence of the C3 species, the warm-season perennial C4 grass, Cynodon dactylon L., played a preponderant role in maintaining substantial E rates contributing to soil water depletion. In this study, we assessed the effects of the most relevant biophysical factors on surface conductance (gs) and E.We found that the Priestley–Taylor coefficient and gs were substantially reduced when the average volumetric soil moisture content in the top 15 cm of the soil profile dropped below 14%. With abundant soil moisture and leaf area index (LAI) greater than 1, the evaporative fractions (lE/Rn) were linearly related to LAI (R2 = 0.73). The decoupling coefficient (V) ranged from a maximum of about 0.7, under non-limiting soil moisture conditions, to a minimumof about 0.1, under soil moisture deficit. This suggests that E was strongly controlled by the vapour pressure deficit of the air and gs during the periods with limiting soil moisture. |
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The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern PortugalMediterranean grasslandEddy covarianceenergy partitioningevapotranspirationdroughtsurface conductancedecoupling coefficientWe studied the seasonal and interannual variation in surface energy fluxes – net radiation (Rn), soil heat (G), sensible heat (H) and latent heat (lE) fluxes – and water vapour exchange above a Mediterranean C3/C4 grassland in Portugal, during two hydrological years, i.e., the period from 1 October to 30 September of the next year, of contrasting rainfall. The first year, 2004–2005, was dry, with total precipitation 45% below the long-term mean (669 mm), whereas the following, 2005–2006, was normal, with total precipitation only 12% above the long-term mean. Soil water availability and plant canopy growth were the most important factors in determining the seasonal and interannual variation in energy partitioning. During autumn, winter and early spring the ratio lE/Rn dominated over H/Rn, in the two years of the study, whereas on an annual basis, the major portion of Rn was consumed in H and lE in the dry and normal years, respectively. The total annual evapotranspiration (E) and its daily maximum were 316 mmand 2.8 mmper day, respectively, for the dry year, and 481mmand 4.5 mmper day for the normal year. After the senescence of the C3 species, the warm-season perennial C4 grass, Cynodon dactylon L., played a preponderant role in maintaining substantial E rates contributing to soil water depletion. In this study, we assessed the effects of the most relevant biophysical factors on surface conductance (gs) and E.We found that the Priestley–Taylor coefficient and gs were substantially reduced when the average volumetric soil moisture content in the top 15 cm of the soil profile dropped below 14%. With abundant soil moisture and leaf area index (LAI) greater than 1, the evaporative fractions (lE/Rn) were linearly related to LAI (R2 = 0.73). The decoupling coefficient (V) ranged from a maximum of about 0.7, under non-limiting soil moisture conditions, to a minimumof about 0.1, under soil moisture deficit. This suggests that E was strongly controlled by the vapour pressure deficit of the air and gs during the periods with limiting soil moisture.ElsevierRepositório da Universidade de LisboaAires, L.M.Pio, C.A.Pereira, J.S.2013-10-10T10:52:03Z20082008-01-01T00:00:00Zinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/articleapplication/pdfhttp://hdl.handle.net/10400.5/6000eng"Agricultural and Forest Meteorology". ISSN 0168-1923. 148 (2008) 565-5790168-1923info:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2023-03-06T14:36:52ZPortal AgregadorONG |
dc.title.none.fl_str_mv |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
title |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
spellingShingle |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal Aires, L.M. Mediterranean grassland Eddy covariance energy partitioning evapotranspiration drought surface conductance decoupling coefficient |
title_short |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
title_full |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
title_fullStr |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
title_full_unstemmed |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
title_sort |
The effect of drought on energy and water vapour exchange above a mediterranean C3/C4 grassland in Southern Portugal |
author |
Aires, L.M. |
author_facet |
Aires, L.M. Pio, C.A. Pereira, J.S. |
author_role |
author |
author2 |
Pio, C.A. Pereira, J.S. |
author2_role |
author author |
dc.contributor.none.fl_str_mv |
Repositório da Universidade de Lisboa |
dc.contributor.author.fl_str_mv |
Aires, L.M. Pio, C.A. Pereira, J.S. |
dc.subject.por.fl_str_mv |
Mediterranean grassland Eddy covariance energy partitioning evapotranspiration drought surface conductance decoupling coefficient |
topic |
Mediterranean grassland Eddy covariance energy partitioning evapotranspiration drought surface conductance decoupling coefficient |
description |
We studied the seasonal and interannual variation in surface energy fluxes – net radiation (Rn), soil heat (G), sensible heat (H) and latent heat (lE) fluxes – and water vapour exchange above a Mediterranean C3/C4 grassland in Portugal, during two hydrological years, i.e., the period from 1 October to 30 September of the next year, of contrasting rainfall. The first year, 2004–2005, was dry, with total precipitation 45% below the long-term mean (669 mm), whereas the following, 2005–2006, was normal, with total precipitation only 12% above the long-term mean. Soil water availability and plant canopy growth were the most important factors in determining the seasonal and interannual variation in energy partitioning. During autumn, winter and early spring the ratio lE/Rn dominated over H/Rn, in the two years of the study, whereas on an annual basis, the major portion of Rn was consumed in H and lE in the dry and normal years, respectively. The total annual evapotranspiration (E) and its daily maximum were 316 mmand 2.8 mmper day, respectively, for the dry year, and 481mmand 4.5 mmper day for the normal year. After the senescence of the C3 species, the warm-season perennial C4 grass, Cynodon dactylon L., played a preponderant role in maintaining substantial E rates contributing to soil water depletion. In this study, we assessed the effects of the most relevant biophysical factors on surface conductance (gs) and E.We found that the Priestley–Taylor coefficient and gs were substantially reduced when the average volumetric soil moisture content in the top 15 cm of the soil profile dropped below 14%. With abundant soil moisture and leaf area index (LAI) greater than 1, the evaporative fractions (lE/Rn) were linearly related to LAI (R2 = 0.73). The decoupling coefficient (V) ranged from a maximum of about 0.7, under non-limiting soil moisture conditions, to a minimumof about 0.1, under soil moisture deficit. This suggests that E was strongly controlled by the vapour pressure deficit of the air and gs during the periods with limiting soil moisture. |
publishDate |
2008 |
dc.date.none.fl_str_mv |
2008 2008-01-01T00:00:00Z 2013-10-10T10:52:03Z |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/article |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://hdl.handle.net/10400.5/6000 |
url |
http://hdl.handle.net/10400.5/6000 |
dc.language.iso.fl_str_mv |
eng |
language |
eng |
dc.relation.none.fl_str_mv |
"Agricultural and Forest Meteorology". ISSN 0168-1923. 148 (2008) 565-579 0168-1923 |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
application/pdf |
dc.publisher.none.fl_str_mv |
Elsevier |
publisher.none.fl_str_mv |
Elsevier |
dc.source.none.fl_str_mv |
reponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação instacron:RCAAP |
instname_str |
Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação |
instacron_str |
RCAAP |
institution |
RCAAP |
reponame_str |
Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
collection |
Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) |
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1777302101705097216 |