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Title: Vegetation-climate feedbacks in the conversion of tropical savanna to grassland

Abstract

Tropical savannas have been heavily impacted by human activity, with large expanses transformed from a mixture of trees and grasses to open grassland and agriculture. The National Center for Atmospheric Research (NCAR) CCM3 general circulation model, coupled with the NCAR Land Surface Model, was used to simulate the effects of this conversion on regional climate. Conversion of savanna to grassland reduced precipitation by approximately 10% in four of the five savanna regions under study; only the northern African savannas showed no significant decline. Associated with this decline was an increase in the frequency of dry periods within the wet season, a change that could be particularly damaging to shallow-rooted crops. The overall decline in precipitation is almost equally attributable to changes in albedo and roughness length. Conversion to grassland increased mean surface air temperature of all the regions by 0.5 C, primarily because of reductions in surface roughness length. Rooting depth, which decreases dramatically with the conversion of savanna to grassland, contributed little to the overall effect of savanna conversion, but deeper rooting had a small positive effect on latent heat flux with a corresponding reduction in sensible heat flux. The authors propose that the interdependence of climate and vegetationmore » in these regions is manifested as a positive feedback loop in which anthropogenic impacts on savanna vegetation are exacerbated by declines in precipitation.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of Texas, Austin, TX (US)
Sponsoring Org.:
National Science Foundation (NSF); National Institute for Global Environmental Change; USDOE
OSTI Identifier:
20075724
Resource Type:
Journal Article
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 13; Journal Issue: 9; Other Information: PBD: 1 May 2000; Journal ID: ISSN 0894-8755
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; TROPICAL REGIONS; CLIMATES; TERRESTRIAL ECOSYSTEMS; C CODES; N CODES; TREES; GRAMINEAE; ATMOSPHERIC PRECIPITATIONS; ENVIRONMENTAL IMPACTS; AMBIENT TEMPERATURE

Citation Formats

Hoffmann, W.A., and Jackson, R.B. Vegetation-climate feedbacks in the conversion of tropical savanna to grassland. United States: N. p., 2000. Web. doi:10.1175/1520-0442(2000)013<1593:VCFITC>2.0.CO;2.
Hoffmann, W.A., & Jackson, R.B. Vegetation-climate feedbacks in the conversion of tropical savanna to grassland. United States. doi:10.1175/1520-0442(2000)013<1593:VCFITC>2.0.CO;2.
Hoffmann, W.A., and Jackson, R.B. Mon . "Vegetation-climate feedbacks in the conversion of tropical savanna to grassland". United States. doi:10.1175/1520-0442(2000)013<1593:VCFITC>2.0.CO;2.
@article{osti_20075724,
title = {Vegetation-climate feedbacks in the conversion of tropical savanna to grassland},
author = {Hoffmann, W.A. and Jackson, R.B.},
abstractNote = {Tropical savannas have been heavily impacted by human activity, with large expanses transformed from a mixture of trees and grasses to open grassland and agriculture. The National Center for Atmospheric Research (NCAR) CCM3 general circulation model, coupled with the NCAR Land Surface Model, was used to simulate the effects of this conversion on regional climate. Conversion of savanna to grassland reduced precipitation by approximately 10% in four of the five savanna regions under study; only the northern African savannas showed no significant decline. Associated with this decline was an increase in the frequency of dry periods within the wet season, a change that could be particularly damaging to shallow-rooted crops. The overall decline in precipitation is almost equally attributable to changes in albedo and roughness length. Conversion to grassland increased mean surface air temperature of all the regions by 0.5 C, primarily because of reductions in surface roughness length. Rooting depth, which decreases dramatically with the conversion of savanna to grassland, contributed little to the overall effect of savanna conversion, but deeper rooting had a small positive effect on latent heat flux with a corresponding reduction in sensible heat flux. The authors propose that the interdependence of climate and vegetation in these regions is manifested as a positive feedback loop in which anthropogenic impacts on savanna vegetation are exacerbated by declines in precipitation.},
doi = {10.1175/1520-0442(2000)013<1593:VCFITC>2.0.CO;2},
journal = {Journal of Climate},
issn = {0894-8755},
number = 9,
volume = 13,
place = {United States},
year = {2000},
month = {5}
}