1997–1998 ENSO-related drought event, Indonesian peat fires
released an estimated 0.8–2.6 Pg C [40], and during 2000–2006,
the average fire emissions from this region increased to 128 ± 51
(1r) Tg C year1 [56]. The already strong relationship between fire
emissions and drought is likely to strengthen due to positive feedback,
because increased greenhouse gas concentrations may lead
to more frequent or severe drought events [23].
Forest fires increase atmospheric aerosol concentrations, leading
to regional and global impacts on the solar heating of the surface
and atmosphere as well as the hydrological cycle [5].
Emissions of aerosols could lead to either warming or cooling on
a regional scale, which are depending on factors such as aerosol
composition, the albedos of both the Earth’s surface and clouds,
and so on. Although considerable uncertainty remains, the risk of
Amazonian drought may increase due to decreasing aerosol pollution
and increased greenhouse gases [18]. A strong relationship
between dry-season aerosol optical depth (AOD) and dry-season
precipitation also suggests a positive feedback mechanism
between aerosols and drought, this may contribute to intensified
drought under climate change [5]. Climate modeling studies suggest
that these aerosols may lengthen or intensify periods of
drought in the Amazon [55] and in Indonesia [18]. Drought may
also produce aerosols directly, such as the dust aerosols dramatically
increased during drought years in the Sahel [35].
The interactions between drought, fire, aerosols and greenhouse
gases are quite complex. Whereas greenhouse gases release the
emission of thermal radiation to space, thus warming the surface,
aerosols should reflect and absorb solar radiation (the aerosol
direct effect) and modify cloud properties (indirect effect), thereby
cooling the surface. These disturbances on the radiation balance
are very different and need different research approaches [29].