Document: RUT-3-18-1

Effects of coarse scale land use change on primary production and climate.

DEFRIES, R.S.* ^1,2

Department of Geography, University of Maryland College Park ¹
Earth Systems Science Interdisciplinary Center, University of Maryland College Park ²

Abstract:
Land cover conversion from human activity potentially affects a number of biophysical and biogeochemical processes. Here we investigate the effects on primary production of the biosphere, climate, and linkages between the two. Using a satellite-derived global map of current land cover and a map approximating global land cover in the absence of human modification of the landscape, we investigate the effects of land cover conversion using two models: the Carnegie-Ames Stanford Approach (CASA) terrestrial carbon model and a land surface model linked to a General Circulation Model (SiB2-CSU GCM). The results from CASA indicate that high-input temperate agriculture has a higher net primary production than the vegetation that would exist in the absence of human activity. On the other hand, land cover conversion in the tropics and subtropics has reduced net primary production, in some locations up to 90 percent. Results using the same land cover maps in the linked SiB2-CSU GCM suggest that the changes in physiological activity from land cover conversion affect climate as well. In temperate latitudes, land cover conversion acts to cool air surface temperatures up to .7 degrees C in summer and 1.32 degrees in winter. This cooling results from both 1) morphological changes in vegetation which increase albedo and 2) physiological changes which increase summertime latent heat fluxes due to increased stomatal conductance. Conversely in the tropics and subtropics where vegetation is less physiologically active than the undisturbed vegetation, conversion acts to warm air surface temperature by .9 degrees C in both summer and winter. The overall effect of land cover conversion is to offset some of the warming from the enhanced greenhouse effect in temperate latitudes and to exacerbate it in the tropics. The results from the two models highlight the linkages between physiologic processes of the vegetation and biophysical processes affecting climate. The results also suggest that effects of land cover conversion on productivity of the biosphere and on climate vary from region to region.

Keywords: land use change, climate change

This abstract is being presented at: 1:30 PM in session:
Symposium # 17: Land Use and Land Cover Change: The Last Century and Prospects for the 21st Century.