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    Observations of Albedo and Radiation Balance over Postforest Land Surfaces in the Eastern Amazon Basin

    Source: Journal of Climate:;1997:;volume( 010 ):;issue: 005::page 919
    Author:
    Giambelluca, Thomas W.
    ,
    Hölscher, Dirk
    ,
    Bastos, Therezinha X.
    ,
    Frazão, Reginaldo R.
    ,
    Nullet, Michael A.
    ,
    Ziegler, Alan D.
    DOI: 10.1175/1520-0442(1997)010<0919:OOAARB>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: Regional climatic change, including significant reductions in Amazon Basin evaporation and precipitation, has been predicted by numerical simulations of total tropical forest removal. These results have been shown to be very sensitive to the prescription of the albedo shift associated with conversion from forest to a replacement land cover. Modelers have so far chosen to use an ?impoverished grassland? scenario to represent the postforest land surface. This choice maximizes the shifts in land surface parameters, especially albedo (fraction of incident shortwave radiation reflected by the surface). Recent surveys show secondary vegetation to be the dominant land cover for some deforested areas of the Amazon. The characteristics of secondary vegetation as well as agricultural land covers other than pasture have received little attention from field scientists in the region. This paper presents the results of field measurements of radiation flux over various deforested surfaces on a small farm in the eastern Amazonian state of Pará. The albedo of fields in active use was as high as 0.176, slightly less than the 0.180 recently determined for Amazonian pasture and substantially less than the 0.19 commonly used in GCM simulations of deforestation. For 10-yr-old secondary vegetation, albedo was 0.135, practically indistinguishable from the recently published mean primary forest albedo of 0.134. Measurements of surface temperature and net radiation show that, despite similarity in albedo, secondary vegetation differs from primary forest in energy and mass exchange. The elevation of midday surface temperature above air temperature was found to be greatest for actively and recently farmed land, declining with time since abandonment. Net radiation was correspondingly lower for fields in active or recent use. Using land cover analyses of the region surrounding the study area for 1984, 1988, and 1991, the pace of change in regional-mean albedo is estimated to have declined and appears to be leveling at a value less than 0.03 above that of the original forest cover.
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      Observations of Albedo and Radiation Balance over Postforest Land Surfaces in the Eastern Amazon Basin

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    contributor authorGiambelluca, Thomas W.
    contributor authorHölscher, Dirk
    contributor authorBastos, Therezinha X.
    contributor authorFrazão, Reginaldo R.
    contributor authorNullet, Michael A.
    contributor authorZiegler, Alan D.
    date accessioned2017-06-09T15:34:44Z
    date available2017-06-09T15:34:44Z
    date copyright1997/05/01
    date issued1997
    identifier issn0894-8755
    identifier otherams-4763.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4186878
    description abstractRegional climatic change, including significant reductions in Amazon Basin evaporation and precipitation, has been predicted by numerical simulations of total tropical forest removal. These results have been shown to be very sensitive to the prescription of the albedo shift associated with conversion from forest to a replacement land cover. Modelers have so far chosen to use an ?impoverished grassland? scenario to represent the postforest land surface. This choice maximizes the shifts in land surface parameters, especially albedo (fraction of incident shortwave radiation reflected by the surface). Recent surveys show secondary vegetation to be the dominant land cover for some deforested areas of the Amazon. The characteristics of secondary vegetation as well as agricultural land covers other than pasture have received little attention from field scientists in the region. This paper presents the results of field measurements of radiation flux over various deforested surfaces on a small farm in the eastern Amazonian state of Pará. The albedo of fields in active use was as high as 0.176, slightly less than the 0.180 recently determined for Amazonian pasture and substantially less than the 0.19 commonly used in GCM simulations of deforestation. For 10-yr-old secondary vegetation, albedo was 0.135, practically indistinguishable from the recently published mean primary forest albedo of 0.134. Measurements of surface temperature and net radiation show that, despite similarity in albedo, secondary vegetation differs from primary forest in energy and mass exchange. The elevation of midday surface temperature above air temperature was found to be greatest for actively and recently farmed land, declining with time since abandonment. Net radiation was correspondingly lower for fields in active or recent use. Using land cover analyses of the region surrounding the study area for 1984, 1988, and 1991, the pace of change in regional-mean albedo is estimated to have declined and appears to be leveling at a value less than 0.03 above that of the original forest cover.
    publisherAmerican Meteorological Society
    titleObservations of Albedo and Radiation Balance over Postforest Land Surfaces in the Eastern Amazon Basin
    typeJournal Paper
    journal volume10
    journal issue5
    journal titleJournal of Climate
    identifier doi10.1175/1520-0442(1997)010<0919:OOAARB>2.0.CO;2
    journal fristpage919
    journal lastpage928
    treeJournal of Climate:;1997:;volume( 010 ):;issue: 005
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
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