chapter - Atmospheric and Oceanic Science

Considering the non-linear interaction between the atmosphere and vegetation
through the sensible, latent and momentum transfer, radiation and that, in the long
time scales, climate exerts the main control on vegetation and that the biome type
influences climate, it is possible to conceive the existence of multiple equilibrium
of the climate/vegetation system. Oyama and Nobre (2003) coupled a dynamical
biome model to the global climate model of Center for Weather Forecasting and
Climate Research in Brazil in order to study the equilibrium solutions. They have
shown the possibility of two stable solutions for the particular case of the biomes
of South America: the first stable solution provides a biome distribution similar to
the observed in the present; the second solution is characterized the savannah in the
eastern Amazon and semi-desert in the Northeast region of Brazil and the Atlantic
Forest domain extended to the Central region of Brazil (Nobre et al. Oyama, 2004).
Nevertheless, it is still unclear the influence of land surface variations in
explaining the slightly positive rainfall trends documented in southern Amazonia
since the middle 1970's (Marengo 2004) and the significant positive trends detected
in rainfall and streamflow over the subtropical portion of the La Plata Basin
(Liebmann et al. 2002). Strong correlation with the SST anomalies in the Pacific
and Atlantic oceans is usually detected and therefore a direct signal between deforestation
and precipitation changes in the long term is not evident. More recent
results have suggested different trajectories of the precipitation reduction as a function
of deforestations (Avissar et al. 2002). Figure 10.1 (an adaptation of Figure 1
of Avissar et al., 2002) suggests three different patterns, among many possible speculated
options. One option suggests an increase in precipitation as a result of partial
deforestation maybe due to the mesoscale circulations triggered by the deforestation
as in Silva Dias et al. (2002).
Precipitation
Background on other regional aspects: Land use change, aerosols and trace gases
Deforestation
134
Fig. 10.1.
Conceptual impact of
deforestation in
precipitation. The lines
indicate results of three
different models among
many possible.