Five Source Copies

2664 VOLUME 15 J O U R N A L O F C L I M A T E

q 2002 American Meteorological Society

Stable Isotopes as Validation Tools for Global Climate Model Predictions of the Impact

Environment, Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales, Australia

Department of Applied Physics, University of Technology, Sydney, Broadway, New South Wales, Australia

Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia

(Manuscript received 7 May 2001, in final form 12 November 2001)

This paper examines changes in isotopic abundances for 18 O and deuterium in precipitation over the Amazon

basin based on data in the Global Network on Isotopes in Precipitation (GNIP) database from the International

Atomic Energy Agency (IAEA)/WMO. The analysis is conducted in the context of recent changes (and anticipated

future changes) to the land surface hydrology as a result of tropical deforestation. Statistically significant temporal

changes (1965–90) in selected stable isotopic signatures in the Amazon have been compared with global climate

model (GCM) predictions revealing notable differences. For example, the wet season deuterium excess differences

between Belem and Manaus, Brazil, are consistent with recent GCM simulations only if there has been a relative

increase in evaporation from nonfractionating water

. . .
n the early 1960s and about 12 percent (3.45 million hectares) in 1998.[2] Very low grain yields, which rose from some 0.6 metric tons per hectare (t/ha) in 1961 to some 0.8 t/ha in 1998, were supported by manure from livestock grazing on arable land not currently used for farming--the much larger area farther from the homesteads. In Niemeijer and Mazzucato's bar graph of soil fertility in the farmed and homestead soils (compound fields) versus other land such as bush fields, it appears that there is a considerable ongoing transfer of plant nutrients from the grazed areas to the farmed and homestead fields.[3] The effect is particularly clear for potassium, which is concentrated near the homestead through livestock excreta (because livestock are gathered in the evening near the homestead). The slow increase in yields over the last few decades--less than 2 percent per year-is probably due to a gradual intensification of crop management, as posited by Niemeijer and Mazzucato. This intensification includes more careful plant nutrient transfer to farmed land through livestock, somewhat better weeding, varietal selection, and a change in fertilizer use on grain crops from zero in the early 1960s to some 1.5 kilograms per hectare (kg/h
. . .

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Approximate Word count = 2064
Approximate Pages = 8 (250 words per page)

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