Decoupling of ENSO and fires in insular Southeast Asia from 2001-2010

Eight-day active fire time series (2001-May 2010) in western, insular Southeast Asia were analyzed to evaluate whether the relationship between the El Niño Southern Oscillation (ENSO) and fires has changed through time consistent with the hypothesis that fires and climate forcings are becoming decoupled as deforestation has continued in the region. The study period was marked by three major fire peaks in 2002, 2006 and 2009-2010 coinciding with three El Niño events. Maximum cross correlation coefficients (MCC) between lagged ENSO sea-surface temperature indices and fire counts (raw and seasonally detrended) were modest (≤ 0.50) and showed a general decrease for most land cover types from 2001-2006 to 2007-May 2010. A notable exception was peat swamp forest where the MCC increased slightly between the two periods for all indices except Niño3. A measure of annual seasonality also revealed that fires in peat swamp forest, lowland forest and secondary formations from 2007-May 2010 were more seasonal than fires during 2001-2006. Overall, the evidence suggests that fires and ENSO are becoming decoupled in the region and that forest types such as peat swamp and lowland forest may be experiencing more seasonal fires. We hypothesize that the decoupling occurs because of a stabilization in land use and establishment of permanent crops. We thus expect that fires will diminish in these areas as permanent plantations (primarily oil palm) are established and incentives to protect valuable crops outweigh incentives to convert land for cultivation.