A Numerical Investigation of Changes in Energy and Carbon Cycle Balances under Vegetation Transition due to Deforestation in the Asian Tropical Region

Abstract

Temporal progress of forest reduction by deforestation in the Asian tropical region was simulated using a global climate model that included a new land-surface ecosystem model. The horizontal resolution of the model was 1.875°. Two experimental areas were defined: the Indochina peninsula (ICP) area, and the Maritime Continent (MTC) area. With a control simulation under the actual vegetation condition, a grassland experiment (C4 experiment) and a bare-soil experiment (BS experiment) were carried out. Forest vegetation in the experimental areas was gradually changed (at the latest actual rate) to non-forest type vegetation. The natural growth of C₄ grass was reproduced in the C4 experiment, and the plant growth was deterred in the BS experiment. Each experiment was run for 100 model years. Temporal changes of the energy and the carbon cycle balances under the vegetation transition were examined. Compared with the control, the net radiation (RNE) decreased because of the increase in the land surface albedo. The sensible heat flux decreased because of the decreases in RNE and other particular reasons. The results for latent heat flux (E) in this study differed from those in our previous study. In the C4 experiment, E increased, especially in the ICP area; in the BS experiment, E decreased in both experimental areas. In the MTC area, the surface temperature in the C4 experiment increased because of the large influence of decreased precipitation. Decreases of the soil wetness in the C4 experiment were more significant in the MTC area, due to increased transpiration and the decreased precipitation. The change from forest vegetation to C₄ grass vegetation induced the reduction of carbon absorption by the land surface. Continuous deforestation in the Asian tropical region certainly induces the elevations of the global atmospheric carbon dioxide concentrations, even if the deforested area is not replaced by bare soil surface condition.