Tropical forest fire is becoming an important environmental issue in
the Southeast Asia region. This is because the recurrent haze in the region
has been attributed to the gas emissions (Radojevic, 2003) and addition
of particulates to the atmosphere by periodic forest fire occurring in
the region (Heil and Goldammer, 2001; Abbas et al., 2004) and also
an increased in respiratory diseases such as asthma (Emmanuel, 2000; Kunii
et al., 2002; Mott et al., 2005) during the haze episode.
Most of these hazes were from forest fires in Sumatra and transported
to Singapore and Kuala Lumpur by prevailing southeasterly wind (Koe et
al., 2001). It also has an impact on the regions economy such as the
tourism industry in the region (Shahwahid and Jamal, 1998).
In order to mitigate these effects there is a need to forecast the potential
of fire and this can be done using fire danger indices such as MacArthur
Fire Meter (McArthur, 1963), Canadian Fire Weather Index (CFWI) and also
Keetch Byram Drought Index (KBDI). Many studies have attempted to use
KBDI and relate with forest fire risk (Heim, 2002; Dolling et al.,
2005) and map KBDI of many stations (Janis et al., 2002) to facilitate
fire potential monitoring.
Keetch Byram Drought Index (KBDI) is basically a mathematical system
for relating current and recent weather conditions to a potential or expected
fire behavior. It is a number representing the net effect of evapotranspiration
and precipitation in producing cumulative moisture deficiency in deep
duff and upper soil layers (Keetch and Byram, 1968). This Index expresses
drought as an index on a scale from 0 to 2000, based on the moisture content
of the soil. Zero is the point of no moisture deficiency and 2000 is the
maximum drought level possible (Buchholz and Weidemann, 2000).
In Malaysia, no study on Keetch Byram Drought Index (KBDI) and its application
has been conducted. This study will derive KBDI and analyse the temporal
trends of the selected stations.
MATERIALS AND METHODS
Four stations, Kota Bharu (Kelantan), Kuching (Sarawak), Sandakan (Sabah)
and Subang (Selangor) were chosen for this study (Table
1). The stations were selected since they represent different climatic
variations of the country. Also occurrence of forest fires have been reported
in the vicinity of these stations. Maximum daily air temperature and total
daily rainfall from 1st January 1990 to 31st December 1995 were used to
derive the KBDI.
||Location of the 4 selected stations
||Levels of Keetch Byram Drought Index (KBDI)
The KBDI was determined using method developed by Keetch and Byram (1968)
and the calculation was automated using a software developed by Ainuddin
and Saidy (2001).
The KBDI is calculated by adding the change in the dryness index on each
day to the KBDI from the previous day. On each day, a value for the soil
water depletion in mm is computed as the KBDI from the previous day minus
the net rainfall (mm) on the current day. The net precipitation (mm) is
calculated as the recorded precipitation (mm) minus 5.08 mm, which
corresponds to the rainfall in inches minus 0.2 inch that was used
by Keetch and Byram (1968). The soil moisture depletion is calculated
as 203.2 mm minus Q (mm), which corresponds to 800 (hundredths of
inches) minus Q (hundredths of inches) (Snyder et al., 2006).
Daily maximum temperature and daily total precipitation of each stations
were used to derive daily KBDI to give a total of 2191 daily KBDI. Daily
KBDI were analysed using frequency analysis and descriptive statistics.
In translating KBDI values into operational practicality, Keetch and
Byram (1968) categorized KBDI into three levels (Table 2);
low fire danger, moderate fire danger and high fire danger. Low fire danger
means that soil and fuel moisture is high. Most fuels will not readily
ignite or burn. At moderate fire danger, fires more readily burn and will
carry across an area with no gaps. Heavier fuels will still not readily
ignite or burn. At high fire danger fires will readily burn in all directions
exposing minerals soils and large fuels may burn or smolders for several
days creating possible smoke and control problems (Keetch and Byram, 1968).
Table 3 shows the descriptive statistics of daily Keetch
Byram Drought Index (KBDI) value for 4 stations.
||Mean, maximum, minimum and standard deviation of daily
KBDI values of selected stations
||Monthly mean KBDI for the four stations (1990 to 1995)
The Kota Bharu stations
KBDI values for mean, maximum and minimum were 1191 units, 1982 units
and 53 units respectively. As for the Kuching station, the KBDI value
for mean, maximum and minimum were 728 units, 1769 units and 36 units
respectively. Meanwhile at the Sandakan station, the daily KBDI value
for mean, maximum and minimum were recorded 993 units, 1868 units and
43 units respectively. Lastly, the KBDI values for mean, maximum and minimum
at Subang station each recorded 1055 units, 1896 units and 41 units.
The highest mean KBDI was recorded in Kota Bharu station with the value
of 1191 units while the lowest KBDI value for mean was recorded in Kuching
station with the value of 728 units.
Kota Bharu highest monthly mean KBDI value was recorded in February with the
value of 1550 in 6 year period, while the lowest was in November with the value
of 380. Beginning from May, the KBDI value decreases until December and from
January to March, the KBDI value increases constantly and then dropped in April.
Highest monthly mean KBDI value for Kuching during the study period was
1120 in July; meanwhile the lowest was recorded 240 in January. The KBDI
value increases from February to September, but the value dropped from
the month of October to December.
From the Fig. 1, the highest monthly mean KBDI value
for Sandakan was recorded 1355 in April in six-year period, while the
lowest was 380 in December. From January to June, the KBDI value increased
constantly and then dropped from July to December.
The highest KBDI value for Subang was 1370 in July; meanwhile the lowest
KBDI value recorded 680 in December.
||Monthly fire danger severity for 4 stations (1990 to
||Frequency analysis of KBDI during the study period (1990-1995)
From January to February, the KBDI
value increase constantly, then dropped from March to May. Beginning from
July, the KBDI value decreases until December.
Figure 2 shows monthly variations of three categories
of KBDI according to stations. Each station shows different monthly patterns
with Kota Bharu exhibits 9 months of moderate and high fire danger categories.
Kuching shows only two months of moderate fire danger while the rest falls
under low fire danger.
In Table 4, Kota Baru has the highest number of days
in the high fire danger with 734 days fall into that category. KBDI level
showed that the areas within the Kuching station faces low fire danger
as 1497 days the KBDI falls under low fire danger while high fire danger
occur 120 days. This is also true for Sandakan station which 1056 days
falls under low fire danger. However, for 424 days the KBDI falls into
high fire danger category. Areas within the Subang station face moderate
fire risk with 926 days recorded in moderate fire danger and 366 days
of KBDI recorded in high fire danger category.
Monthly mean KBDI variations among the stations show different patterns.
Monthly mean KBDI for Kota Bharu station is lowest during December while
highest during March. For the Kuching monthly mean KBDI, the pattern shows
more irregularity but has lowest KBDI value in December with high KBDI
values in March and June. KBDI monthly mean variation for Sandakan shows
low value during December with high KBDI during March to June. KBDI trend
for Subang is following the trend of other stations with KBDI value lowest
during December. The KBDI value increases in March and peaked in June.
Figure 2 visually expressed monthly fire danger severity
(Hall and Gwamela, 1985) for the four stations. Among the stations Kota
Bahru has two months of high fire risk and eight months of moderate fire
risk. In fact among the stations studied, only Kota Bahru has months of
high fire risk. Subang station has seven months of moderate fire risk
while Sandakan has continuous five months of moderate fire risk. Kuching
has the lowest risk which has only two months of moderate risk. The pattern
in which months occurred is different at each station. This is due to
the geographical location of each station that influenced the different
rainfall pattern each station.
The daily KBDI in each station shows temporal trend and can be used for
forest fire management. Hall and Gwamela (1985) analysis of fire danger
indices at Tanzania shows that this information can be used to develop
fire control activity time table. Period of days when KBDI`s are in high
fire danger category can be determined and this information can be used
to plan for presuppression activities such putting the forest fire management
team on alert and be ready to fight the fire. Period when the KBDI`s are
low, the forest fire management team can use this occasion for training
and maintenance of the equipment. Understanding the period of high and
low of KBDI can be used to relate with total areas burnt (Dolling et
al., 2005) and also help to plan allocation of resources (Chan et
al., 2000) for forest fire management and planning.
The highest monthly mean KBDI value was Kota Bharu station during the
month of January, meanwhile the lowest KBDI was Kuching station also in
January. In terms of forest fire management perspectives, the Kota Bahru
station faces higher risk in January compared to the other stations in
the same month. On the other hand, areas within the Kuching station faces
the lowest risk of fire in January compared to the other stations in the
same months. The information from the daily KBDI can be used for forest
fire management purposes.
We would like to express my appreciation to the Malaysian Meteorological
Department for supplying the meteorological data used in this study.