The Climatic Effects of Deforestation in South and Southeast Asia

Abstract

Deforestation is the removal of the existing natural vegetation cover, especially where the native cover is largely forest. The growth in the world population has increased the clearing of forests to obtain fuel and building material, to grow crops and to raise livestock. Over the past 300 years, 7-11 million km2 of forest has been cleared (Foley et al. 2005). Deforestation can have a devastating impact on biodiversity as about 70% of land dwelling animals and plants are found in forests. Impacts such as land degradation in the absence of forest regrowth, soil erosion and sedimentation in rivers can have a negative impact on the environment. These impacts are discussed in greater detail in the other chapters of the book. Importantly, deforestation can also have strong effects on climate. In the past it was assumed that the local climate determined the vegetation type in a region (Nobre et al. 1991) with the amount of incoming solar radiation, precipitation and soil type determining the vegetation cover of the region. But studies have shown that the atmosphere and the vegetation interact with each other, exchanging energy, moisture and momentum (Zeng et al. 1999) and are in a dynamic equilibrium (Nobre et al., 1991). Therefore any change in vegetation cover can potentially lead to a change in the climate. As deforestation is a pressing problem in most parts of the world it is important to understand the possible consequences of deforestation and the mechanisms by which the change in land cover can alter the climate. The impacts of land cover changes on the atmosphere have been studied extensively using both observations and computer models (Suh and Lee, 2004; Lean and Warrilow, 1989; Kanae et al., 2001; Clark et al., 2001). Previous studies have shown that deforestation can change the surface albedo, surface roughness and the amount of evapotranspiration (evapotranspiration is the combined effect of evaporation from the surface and the transpiration from vegetation) (Gibbard et al., 2005; Oglesby et al., 2010; Hasler et al., 2007) thus, leading to a modification of the surface energy and moisture budgets. In order to determine the full climatic impact of deforestation, it is necessary to understand the behavior of the surface energy and the moisture budgets, as deforestation interacts directly or indirectly with all the components of these budgets. The surface energy budget looks at all the possible sources and sinks of energy at the surface as well as any possible horizontal transport (fluxes) and storage of energy within the seasonally active layer just below the surface. Over land, incoming and reflected solar radiation (shortwave radiation),