Fire – ENSO Relations in the S.E. Asia. / A Remote Sensing Perspective
Although the Niño 3 anomaly presented different temporal trends among the five studied El Niño events (1982-83, 1986-87, 1991-92, 94 and 1997-98), the fire activity occurred constantly during August-October and February-April of the El Niño Year 0 and Year 1 respectively. However, the overall strength of each El Niño event related closely to the corresponding fire magnitude (Figure 4).
Results from the cross correlation analysis not indicate clearly any precise and consistent lag time of ENSO-fire association (Figure 6). Various lag times were observed between the five different El Niño events when cross correlation was applied to the 24-month ENSO-fire series. Calculated lags varies between zero and seven months.  Figure 7. Sum of the 16-months fire counts against the coincident sum of Niño 3 anomaly from January to May of El Niño Year 0 and Year 1 respectively. However, a more clear ENSO-fire relationship was revealed when various time composites of Niño 3 anomaly and fire counts were evaluated. The strongest ENSO-fire association was observed when the total 16-months sum of ENSO index (Niño 3 anomaly), from January of Year 0 to April of Year 1, compared against the total fire activity of the same time period (Figure 7). The stepwise linear regression for the five ENSO-fire pairs resulted in an r-square equal to 0.97 (n = 5, p = 0.002) highly significant within 99% confidence level. Consequently, the 97 per cent of the 16-months fire activity in the whole Borneo during the five studied El Niño periods could be explained by the 16-months ENSO strength as measured by the SSTA in the Niño 3 region of the Pacific Ocean. However, as was mentioned previously, these first sixteen months of each 24-months studied fire event included the majority of the entire detected fire events, representing 81% of the total 10-years fire activity in Borneo. Therefore, if this observed ENSO-fire relation remains consistent in future El -Niño events, it may be possible to predict in advance the all-Borneo fire activity based on predictions of Niño 3 anomaly. Then the accuracy of the derived fire activity would depend primarily on the forecast precision of the Niño 3 anomaly by statistical and/or dynamical-coupled models. Conclusion The spatially low resolution NOAA AVHRR GAC satellite data demonstrated an acceptable performance for documenting and quantitatively measuring fire activity in Borneo during El Niño events. Active fire counts on GAC imagery were derived by applying a developed multispectral fire detection method to the totally 10-years GAC dataset, which corresponds to five El Niño events from 1982 to 1998. The derived fire counts were further adjusted from different cloud coverage and observation time of each GAC image. The majority of fire activity occurred between August-October of the first calendar year (Year 0), and between February-April of the following year (Year 1) in each El Niño event. A strong ENSO-fire relationship was found when the total 16-months sum of ENSO index anomaly in the Niño 3 region of the Pacific Ocean, from January of Year 0 to April of Year 1, plotted against the total fire activity of the same time period (r2 = 0.97, n = 5, p = 0.002). These 16 months counted 80.61% of the total 10-years El Niño related fire activity in Borneo. Acknowledgments Thanks to Luis Giglio from Goddard Space Flight Center, NASA for providing the TRMM-VIRS fire diurnal data for Borneo. The former author supported with a PhD studentship by the State Scholarships Foundation (IKY) of Greece, and travel grants by: University of London Central Research Fund, Remote Sensing and Photogrammetry Society, King’s College London Sargeaunt Travel Fund and Small Grants Scheme. References
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