The distribution of fires in time was further
analyzed and compared to the strength of the El
Nino-Southern Oscillation (ENSO) as measured by
the sea surface temperature anomaly (SSTA) in the
Niño 3 region of the Pacific Ocean. The Niño 3
anomaly followed a somewhat different evaluation
in time over the five El Niño events (1982-83, 1986-
87, 1991-92, 94 and 1997-98) (Figure 1b).
350 4
300 +
Cloud & Time
Normalised Fire Counts
200 4
50 4
T T T T
054-203 4 50 7 38 9 1014]
er
21
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
Conversely, the fire activity presented a strong
seasonality occurring constantly in August-October
and February-April of the El Nifio Year 0 and Year
| respectively (Figure 2). However, the overall
strength of each El Nifio event related closely with
the corresponding observed fire magnitude,
revealing the existence of ENSO-fire link in Borneo.
82/83
86/87 -
91/92
93/94
—— 97198
T T T T T T T T T T T
3 14 15 16 17 18 19 20 21 22 23 24 Month
Figure 2 Active Fire Counts from AVHRR GAC data or Borneo for the 24 month period surrounding five
individual ENSO episodes. The strong seasonality of fire activity in Borneo is clearly depicted in all five
ENSO events, with the majority occurring in August-October of Year 0 or Year |, and February-March-
April of Year 1. The strongest and most prolonged El Niño events (i.e. 1982-83/1997-98 and 1991-94
respectively) were accompanied by the most extreme fire occurrence.
Cross correlation analysis did not indicate clearly
any precise lag time of ENSO-fire association which
moreover is inconsistent among the five El Nifio
events (Figure 3). Various lag times were observed
between the five different El Niño events when
cross correlation was applied to the 24-month
ENSO-fire series. However, indeed there is
undoubtedly an ENSO-fire association, which
according to the cross correlation results, seems to
occur somewhere between simultaneously and in
seven months lag time.
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. The stepwise linear regression for
598
the five ENSO-fire pairs resulted a r-square equal to
0.97 (n = 5, p < 0.001) highly significant (Figure
3f). 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, Figure 2 reveals that these first sixteen
months of each 24-months El -Niño represents the
majority (i.e. 80.6196) of the total 10-years fire
activity in Borneo. Therefore, if this strong ENSO-
fire relation found in the current study remains
consistent in the future El -Nifio events, it may be
possible to predict in advance the all-Borneo fire
activity based on predictions of Nifio 3 anomaly.
Then the accuracy of the derived fire activity would
depend primarily on the forecast precision of the
Nifio 3 anomaly by statistical and/or dynamical-
coupled models.
Intern
