Annual variations in Indonesia's climate are largely determined by the El Niño/Southern Oscillation (ENSO) system. However, extreme drought can also result from the cooling of sea surface temperatures near Sumatra caused by a similar ocean-atmosphere phenomenon--the Indian Ocean Dipole (IOD). These two systems and their past and present relationship to the Asian monsoon are examined in a recent study by Abram et al., reported in Nature. The scientists' findings reveal that drought frequency and duration in Indonesia can be expected to increase with global warming.
Corals Reveal Past Temperature, Precipitation Variability
Utilizing geochemical records from fossil Indonesian corals, the authors were able to reconstruct regional temperature and precipitation variability since the middle Holocene epoch (about 6,500 years ago). Their analysis demonstrated that IOD events in the middle Holocene (and, consequently, cooler and drier conditions in Indonesia) lasted longer than those of today.
Data from computer climate model simulations corroborate these results and suggest that IOD intensification in the middle Holocene was largely due to a strengthened Asian monsoon system during this time. This climatic relationship (between the monsoon and IOD) apparently can have a greater influence over the climate of this region than ENSO, which was weaker in the mid-Holocene.
Future Implications
Most scientists agree that as greenhouse gas (GHG) emissions increase and global temperature rises, the Asian monsoon, which has been decreasing in strength since the middle Holocene, is likely to intensify. A number of uncertainties prevail, however, including the impact of a changing ENSO and the influence of human-produced aerosols.
Still, if the relationships between these climate systems hold, more droughts in Indonesia and possibly throughout the Australasian region, could have substantial socio-economic impacts, including:
- Increased number of forest fires
- Loss of forest habitats
- Increased air pollution
- Negative impacts on agricultural growth seasons
- Reduced hydropower generation
All of these likely physical effects will present greater challenges to Indonesia, which has already lost large tracts of forest to deforestation and illegal logging practices and has a national poverty rate of around 27% (1999 data). Achieving reductions in poverty and furthering sustainable development initiatives are therefore all the more critical.
RELATED LINKS:
News and Views: "Lessons from a distant monsoon" by Overpeck and Cole
