Suppressing Impacts of the Amazonian Deforestation by the Global Circulation Change

Salati and Nobre (1990), in a review of the basinscale water vapor budget of the Amazon Basin analyzed by previous studies, pointed out that evapotranspiration accounts for more than 50% of precipitation. This estimate was later confirmed by Nobre et al. (1991) using the water vapor budget of several studies with various horizontal scales within the Amazon Basin. Note that total evapotranspiration was used for these budget analyses. Actually, only a portion of local evapotranspiration is consumed to maintain local precipitation. The ratio between them is referred to as precipitation recycling, which is an indicator of the importance of land-surface processes in the water balance of the region. With this approach, Eltahir and Bras (1994) showed that about 25%–35% of the rain within the Amazon Basin (over scales of 2500 km) is contributed by evapotranspiration. Using Brubaker et al.’s (1993) simplified rectangular domain, Trenberth (1999) estimated that roughly 34% of the moisture is recycled over the Amazon Basin. Regardless of the precipitation recycling estimated either with total evapotranspiration in the convectional water vapor budget analysis, or with only the portion usable in precipitation recycling as Brubaker et al.’s (1993) argument, all available observational evidence seems to suggest that the Amazonian rainforest is highly effective in recycling precipitation into the atmosphere. It follows that replacing the rainforest by the degraded pasture cover will markedly reduce this highly efficient evapotranspiration. Based on several sources (Instituto Nacional de Pesquisas Espaciais 1989; Fearnside 1987; Fearnside 1990; Skole et al. 1990), Nobre et al. (1991, their Fig. 1) estimated that with the current deforestation rate most of the Amazon rainforest would disappear in less than 100 years. Numerous numerical simulations (e.g., Dickinson and Henderson-Sellers 1988; Shukla et al. 1990; Nobre et al. 1991; Henderson-Sellers et al. 1993; Sud et al. 1996; Lean et al. 1996; and many others) using global climate models predict that when all of the Amazon rainforest is replaced by pasture, there will be Suppressing Impacts of the Amazonian Deforestation by the Global Circulation Change