31

Seasonal Variability of Biomass Open Burning Activities in
the Greater Mekong Sub-Region
Sébastien BONNET and Savitri GARIVAIT*The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi,
126 Pracha-Uthit Road, Bangmod, Tungkru, Bangkok 10140, Thailand
Center for Energy Technology and Environment, S&T Postgraduate Education, andResearch Development Office (PERDO), Commission of Higher Education (CHE), Ministry of Education, Thailand*e-mail: savitri_g@jgsee.kmutt.ac.th

Abstract
The seasonal variability of biomass open burning activities in the Greater Mekong Sub-region (GMS)
with focus on carbon monoxide (CO) and total particulate matter or aerosol (TPM) emissions wasinvestigated in order to document the characteristics of this significant source of air pollutants in the region.
This assessment was performed using remote sensing data on fire hotspots detected by ANDES in
combination with ground observations and data on vegetation land-use of the GMS region. We preparedmonthly gridded emissions maps, to identify vegetation types subject to open burning and the corresponding
spatio- temporal distribution. The results obtained showed that the major types of vegetation subject to open
burning in the GMS region are forests and paddy fields. We also found that vegetation fires mostly take place
during the dry season with a peak occurring during January - April. The quantification and spatio-temporal
distribution of emissions from forest fires and rice residue burning could serve as important information to
support decision making on control strategies that should be formulated at the national level to reduce emissions from biomass open burning and thereby to comply with the ASEAN Agreement on TransboundaryHaze.
Key words: biomass open burning, emissions, Greater Mekong Sub-region, seasonality

1. Introduction
Biomass burning is defined as the combustion of theworld’s living and dead vegetation, including grasslands,
forests and agricultural lands following harvest, for land
clearing and land-use change. Biomass burning is not
limited to one area but is a global phenomenon. It has
been recognized as a key driver of global change (Levine
et al., 1995). Biomass burning is recognized to be one of
the major sources of gaseous and particulate emissions to
the atmosphere (Yamasoe et al., 2000). It contributes toglobal environmental change by affecting local, regionaland global air quality as well as by disrupting rainfall
patterns.
In Southeast Asia, interest in biomass open burning
effectively started in 1997/1998 when a severe haze episode occurred as a result of wildfires in Indonesia, whichwere enhanced by the climatology phenomenon known
as the El Niño-Southern Oscillation (ENSO), which
occurred in that year. The resulting haze covered theentire area of Sumatra and Kalimantan, and extended via
long-range transport up to Malaysia, Singapore and theSouthern part of Thailand. The severity of this disaster
Global Environmental Research
15/2011: 31-37
printed in Japanwas recorded by UNEP as one of the most damaging inhistory for the member countries of the Associationof Southeast Asian Nations or ASEAN. The environmental, economic and social impacts resulting from thesefires, and the resulting transboundary haze pollution,
were profound. The total economic losses in terms offorest destruction, health care due to respiratory disease,land and airtransportation disturbances, and impacts on
agricultural production, tourism activities and othereconomic endeavors were estimated at US$9.3 billion(ASEAN Secretariat, 2004).
Transboundary haze pollution, which leads to severe
air quality problems, occurs during the dry season in bothhemispheres (Crutzen & Andreae, 1990; Andreae, 1991).
In the northern hemisphere the peak period is usuallyobserved during January to March in the region covering
Cambodia, Lao PDR, Myanmar, Thailand and Vietnam,
and in the southern hemisphere during August to October,with transport of haze from Indonesia up to the southernpart of Thailand. To remediate this regional air quality
issue, ASEAN approved the establishment of theASEAN Agreement on Transboundary Haze on the basisof voluntary participation and ratification. Once a©2011 AIRIES32

S. BONNET and S. GARIVAIT

member country decides to ratify it, it is expected todevelop and implement a National Master Plan on OpenBurning Control and an Open Burning Control Plan of
Implementation. Although in Asia biomass open burning
particularly concerns China, India, Indonesia andcountries of the Mekong River Basin Sub-Region includeing Thailand, Cambodia, Lao PDR and Vietnam(Streets et al., 2003), there is still a lack of reliable,
up-to-date information concerning biomass open burningemissions in the Asian region. This is particularly thecase for the Greater Mekong River Basin Sub-region(GMS), so regional air quality modeling and monitoring
remain to be developed to better evaluate the impacts of
those emissions on the regional air quality and climate.
To contribute to mitigation of their emissioins inSoutheast Asia of the above issue, information on thespatial and temporal distribution of biomass open burning in the GMS region has been obtained using a
combination of remote sensing data and ground-based
observations, and Geographic Information System (GIS)
vegetation land cover map. Monthly 12 km × 12 km
gridded emission maps have been produced focusing on
CO and total particulate matter (TPM) to characterize thespatio-temporal distributions of vegetation fires and related quantitative emissions.

part of Vietnam along the border with China and in thesouthern part of Vietnam. In the case of Lao PDR, themain vegetation of the country is forest, while land dedicated to rice cultivation is still limited and spreadthroughout the country. A summary of the land area of
each type of vegetation is reported in Table 1.
From the above information, one can see that
Thailand, with 170,157 km2, has the largest area of forest,
followed by Lao PDR, Cambodia and Vietnam. However,with regard to the ratio of forest land to total land area,
Cambodia and Lao PDR, are largely ahead in the region
with about 60% of the country covered with forest. As forpaddy fields, Thailand and Vietnam possess the highest
coverage with 15%-20% of their national land dedicated

2. Methodology
2.1 Vegetation land cover
A Geographic Information System (GIS) map wasdeveloped for the GMS incorporating a database of digital land use maps for each of the countries of the region.
The map is displayed in Fig. 1. The geographic data andcorresponding attributes were collected for the base Yearof 2000 from governmental agencies responsible for landdevelopment, land use and national statistics. Basedon the information collected, land cover maps werecreated for Thailand, Cambodia, Lao PDR, Vietnam andMyanmar at a 1,250,000 scale. These maps were used asa base GIS layer to classify emissions from biomass open
burning. Three major types of vegetaion were reported on
the maps which include: forests, paddy fields and bushes.
From Fig. 1, it can be observed that paddy fields aremostly located in the central part of Cambodia, in thecentral and northeastern part of Thailand, in the northern

Fig. 1 GMS vegetation map (2000).

Table 1 Land surface of forest and paddy fields in the GMS region.
Type
Forestkm2
Mha(% NL)
Paddy
km2
Mha
(% NL)
National areakm2
Mha

ThailandCambodia

Lao PDR

Vietnam

Total in GMS

170,157
17.02
(33%)

108,990
10.90
(61%)

142,602
14.26
(60%)

58,6135.86(18%)

480,36248.04

105,754
10.58
(21%)

17,024
1.70
(9%)

2,556
0.26
(1%)

48,6114.86(15%)

173,94517.39

514,36151.44

181,035
18.10

236,8023.68

331,03333.10

1,263,229
126.32

Seasonal Variability of Biomass Open Burning Activities in the Greater Mekong Sub-Region

to rice cultivation, which indicates their position as major
world producers of rice.
2.2 Biomass open burning activities
2.2.1 Assessment of biomass burning activities
using satellite data
Biomass burning activities in the GMS region were
investigated using remote sensing data. This method
provides information about the geographic position ofand temporal changes in biomass burning activities. In
this study, information on fire hotspots was retrieved
from a satellite launched under the Asia-Pacific Network
for Disaster mitigation using Earth observation Satellite(ANDES) research program. The Defense Meteorological Satellite Program-Operational Linescan System(DMSP-OLS) sensor enables the detection of areas
where temperatures higher than a threshold, qualified as
the reference temperature of open burning (>150°C), areobserved and identified as hotspots. The resolution of thesatellite sensor is 2.7 km × 2.7 km, which is considered acoarse resolution but is sufficiently fine to indicate thelocation of fires and enable estimation of the area burnt
and related emissions. Based on the sensor resolution, it
was assumed that the size of any fire hotspot was equal to
2.7 km × 2.7 km and therefore that the correspondingarea was subject to burning. The ANDES hotspot data
were collected for the Year 2002, since during that year
there was no major interruption in satellite data record;
and therefore hotspots were collected for the whole year
to enable assessment of temporal changes in open burning activities in the GMS region.
The daily data of fire hotspots were first processed
into monthly data in the form of a GIS map, in order toinvestigate the seasonal variability over a year. An
example of a monthly hotspot map is given in Fig. 2.
Each hotspot was classified according to the type ofvegetation where it was located, by overlaying themonthly hotspot map with the land cover map illustrated
in Fig. 1. This overlay of information enabled thequalitative and quantitative assessment of the type ofbiomass subject to open burning and estimation of related
emissions. In order to systematically geo-reference theposition of the hotspots, a grid map with a resolution of
12 km × 12 km was developed, supporting the development of a systematic emissions map, easy to use formonitoring or modeling biomass burning emissions. The
emissions calculation equation was incorporated into the
GIS to compute the emissions for each 12 km × 12 km
grid based on land cover type. Monthly emissions mapsof CO and TPM from forest fires and paddy field burning
were then obtained, enabling us to investigate the areas
and time periods of biomass open burning activities.
2.2.2 Assessment of areas burnt and related emissions
Properties of smoke emissions from biomass open
burning vary highly under the control of two main
parameters: (1) fuel characteristics and (2) combustion
conditions. These parameters are dependent on thefollowing: density of biomass fuel, fraction of biomass

33

burnt, moisture content, biomass type, combustion phase(ignition, flaming or smoldering), completeness of combustion, wind conditions, etc. (Garivait, 1995; Reid et al.,2005). Taking smoke properties into account, the emission of a compound from biomass burning can be determined based on a series of equations originally developed by Seiler and Crutzen (1980) which represents therelationship between the combustion process and its
emissions, as follows:E x = M biomass × EFx(Eq.1),

where Ex is the emission of compound x (g), Mbiomass
is the mass of biomass subject to burning and expressedon a dry mass basis (kg), and EFx represents the emission
factor of compound x (g/kg biomass).
For forest fires, the mass of biomass, Mbiomass, can be
estimated as follows:

Mbiomass = A × L × FB

(Eq. 2),where A is the area burnt (ha), L is the biomass load or
dry matter density (kg/ha), and FB is the fraction of biomass burnt (burning efficiency).
Currently, data on the area burnt, A, are obtained
either from observations at ground level, by aircraft or byremote sensing; while data on L and FB are generally
from surveys and/or field experiments.
In the case of crop residue burning, the amount of biomass burnt can be determined using a modified version of
the expression given in the IPCC revised guidelines(1996) and also similar to that used by Hao and Liu(1994) or Streets et al., (2003), as follows:

Mbiomass = A × P × N × D × F × FB

(Eq. 3),

Where A is the area of rice cultivation (ha), P is thecrop yield (kg/ha), N is the crop-to-residue ratio (no unit),
D is the fraction of dry matter (no unit), F is the fractionof dry matter crop residue left unused in the field and FB
is the fraction of biomass burnt (burning efficiency). Data
related to A and P can be obtained from national statistics
and those to N, D, F and FB from surveys.
In order to characterize emissions from biomass open
burning with an emphasis on forest fires and rice residue
burning in the GMS region, data related to the parameters
identified in Equations 2 and 3 were collected from several sources, as detailed in Table 2. These parameters, in
combination with information on areas of vegetation
Table 2 Estimates of tropical forest biomass and crop residues
burnt in Asia.
Biomass load range (kg/m2)
Tropical
ForestCrops

10

Residue-to-crop
ratio
1.76c

Rice
a

a

b

Burning efficiency
0.2b

Dry
matterfraction
0.85d,e,f

Dry matterburnt in
Burning efficiency
field
25%d,e89%eIPPC (1996); Levine (2000); cKoopmans and Koppejan (1997), dHao and
Liu (1994); eStreets et al., (2003); fOEP (1990)

34

S. BONNET and S. GARIVAIT

subject to open burning as detected in the form of fire
hotspots by ANDES (see Fig. 2), were used to quantify
the amount of biomass burnt and related emissions overtime and space.
For the calculations of emissions, a review study byAndreae and Merlet (2001) provides a compilation ofpollutant-specific emission factors for various types ofvegetation subject to burning including tropical forestsand crop residues. Those emissions factors were sourced
from a critical review of research works performed overthe past few decades on emission factor measurements
worldwide. In this study, the focus is on emissions of CO
and TPM. The EF for CO was retrieved from Andreae
and Merlet (2001), but that of total particulate matter(TPM) was collected from Levine (2000), since in that
research work the studied emissions were obtained fromexperiments representative of burning conditions in Asia
(Table 3).

Fig. 2 Monthly fire hotspots map (2002).
Table 3 Emission factors of CO and TPM vs. biomass type(g/kg of dry matter).
Biomass type

TropicalforestAgriculturalresidue

ReferenceCO

104 ± 2092 ± 84

Andreae and Merlet(2001)

TPM

20

10

Levine (2000)

3. Results and Discussion
3.1 Biomass open burning activities
The biomass open burning activities observed by
ANDES satellite for Thailand, Cambodia, Lao PDR and
Vietnam, are reported in Fig. 3, in terms of fire counts.
Results from Fig. 3 indicate that the peak season offorest fires in the GMS region occurs during the dry
season running from October to April. In Thailand,
Cambodia and Vietnam, the peak value is found in February, while for Lao PDR this is observed in April. The
highest record is from Thailand, where more than 2,600
fires were counted in February 2002.
Regarding paddy field burning, the peak season isobserved during the period of January – April in Thailand,
Lao PDR and Cambodia. In Vietnam, however, a different pattern is observed with frequent burning activities
occurring throughout the year. In addition, based on theintensity of paddy field burning, Thailand and Vietnam
are far ahead. The particular seasonal pattern of paddy
field burning observed for Vietnam seems to confirm anagro-intensification of rice production in this country.
Based on the fire count data retrieved from ANDES
with satellite sensor resolution of 2.7 km × 2.7 km, thecorresponding area of vegetation burnt (forest and paddy
field) was quantified. The results are reported in Table 4.
Those results show that among the investigatedcountries, Thailand has the highest area of vegetation
burnt with regard to forest and rice residues. In Vietnam,
the total surface of paddy fields burnt is comparable tothat of forests. These results indicate that slash-and-burnis a common practice in Vietnam and Thailand and bothcountries are experiencing an intensification of ricecultivation with an increased number of crops harvested
per year, e.g., 2-3 crops per year in the case of Thailand,in particular in the central part of the country and where
irrigation is available.
3.2 CO and TPM emissions
Following the assessment of areas of forest and paddy
field burnt in each country of the GMS, the corresponding amounts of biomass burnt were estimated using Eq. 2
and Eq. 3 and data from Table 2. On the basis of thisinformation, emissions of CO and TPM were estimatedusing Eq. 1 and the emissions factors reported in Table 3.
The results obtained at the level of the GMS region, wererepresented in the form of monthly gridded emissions
maps of CO and TPM as shown in Figs. 4 and 5, respectively. These two figures seem identical since they arederived from the same hotspots map (see example illustrated in Fig. 2). The gridded emission maps help tovisualize the locations where the numbers of fire counts,
and hence the emissions intensities are high.
From Figs. 4 and 5, and based on the vegetation land
use map, it is observed that for Thailand and Cambodia,
forest fires largely contribute to emissions of pollutants
during March and April, while open burning of paddy
fields is particularly active during the period ofJanuary-February, particularly in the central and theSeasonal Variability of Biomass Open Burning Activities in the Greater Mekong Sub-Region

ThailandCambodia

VietnamLao PDR

35

Fig. 3 Monthly fire counts related to forest fires and paddy field burning in the GMS region for the year 2002.
Table 4 Area burnt per type of biomass and country in 2002.
Area of forest burnt(km2)
Area of rice burnt(km2)

ThailandCambodia

VietnamLao PDR

29,431

13,752

6,360

10,174

11,568

1,153

5,414

175

northeastern regions of Thailand and in the central part ofCambodia around the Mekong delta.
In the case of Lao PDR, as paddy fields and forest
coexist, and the land area where rice is cultivated is very
limited, the burning is observed spread throughout thecountry with very low intensity or frequency. Finally, forVietnam, only rice fields in the south along the borderwith Cambodia are affected by burning and are characterized by a similar intensity throughout the four months
studied, confirming a possible intensification of rice
farming in this region.
The first two months of the year (January and February) is the period corresponding to a dry wintery season
in the GMS region, and therefore to a period where highpressure and cold air masses from China cover thenorthern and northeastern part of Thailand, and thenorthern part of Cambodia, Lao PDR and Vietnam. This
weather condition contributes to a poor dispersion of thepollutants that are emitted in the atmosphere, and therefore to a higher ambient concentration of pollutants. This
is notably the case for particulate matter, the ambientconcentration of which can exceed national standards.

Dry weather conditions also favor fast propagation ofvegetation fires. Hence, it would be particularly necessary to control field burning of rice residues during
January - March, notably in Thailand and Vietnam, thetop two rice producers in the GMS region.

4. Conclusion
Seasonal changes related to biomass open burning in
the GMS region have been observed via the fire hotspots
detected by ANDES-DMSP-OLS and processed togenerate emissions maps. The corresponding GIS database developed as part of these investigations has served
to identify the types of vegetation subject to open burningand spatio- temporal distribution in the GMS region for
the Year 2002.
The results obtained show that Thailand andCambodia are the two countries where forest fires occur
most frequently. On the other hand, paddy field burning
occurs mainly in Thailand and Vietnam, the two top riceproducers in the region. The peak period of such burning
activities runs from January to April, with a peak during

36

S. BONNET and S. GARIVAIT

Fig. 4 Monthly gridded CO emissions maps during January -April (2002).

Fig. 5 Monthly gridded TPM emissions maps during January - April (2002).

January and February for paddy field burning, and Marchand April for forest fires. As this period corresponds to atime of atmospheric stability, it is necessary to discouragesuch open burning activities. In particular, slash and burnagricultural practices are of concern and should be controlled, notably in Thailand and Vietnam where there isan intensification of rice cultivation. This would enable
the reduction of impacts on air quality and support theASEAN Agreement on Transboundary Haze.

Environment, Asia-Pacific Network (APN), andSoutheast Asia Regional Committee for START(SARCS). We would like to express our sincere
appreciation to Land Development Department for the
support on land cover map data. Finally, we also thankSuwajchai Paoprayoon, Agapol Junpen, Orachorn
Kamnoed, and Kanittha Kanokkanjana for their help in
preparing the inputs to this manuscript.

Acknowledgements

References

The authors would like to thank the Joint Graduate
School of Energy and Environment (JGSEE) and thePERDO Center for Energy Technology and Environment
for providing technical facilities and equipments toundertake this work. Special thanks are extended to different national and international funding agencies for thefinancial support to our research on Aerosols from
Biomass Burning to the Atmosphere, including National
Research Council of Thailand, Pollution Control
Department-Thai Ministry of Natural Resources andAndreae, M.O. (1991) Biomass burning: Its history, use, anddistribution and its impact on environmental quality and global
climate. In: Global Biomass Burning: Atmospheric, Climatic,
and Biospheric Implications, p. 3, MIT Press, Cambridge, MA.
Andreae, M.O. and P. Merlet (2001) Emission of trace gases andaerosols from biomass burning, Global Biogeochemical Cycles,
15, (4): 955-966.
ASEAN Secretariat (2004) Guidelines for the Implementation ofControlled Burning Practices, ISBN: 979 - 3496 - 07 - X.
Crutzen, P.J. and M.O. Andreae (1990) Biomass burning in thetropics: Impacts on atmospheric chemistry and biogeochemical
cycles, Science, 250: 1678-1679.

Seasonal Variability of Biomass Open Burning Activities in the Greater Mekong Sub-Region
Garivait, S. (1995) Study of compounds emitted by savannah
burning using a physical chemistry approach – Development ofa dynamic model based on thermo-chemical equilibrium laws
(in French), PhD Thesis, University of Paris 7.
Hao, W.M. and M. Liu (1994) Spatial and temporal distribution oftropical biomass burning. Global Biogeochemical Cycles, 8:495-503.
Intergovernmental Panel on Climate Change (1996) Revised 1996
IPCC Guidelines for National Greenhouse Gas Inventories.
<www.ipcc-nggip.iges.or.jp>
Koopmans, A. and J. Koppejan (1997) Agricultural and forest
fires: Generation, utilization and availability, paper presented at
Regional Consultation on Modern Applications of Biomass
Energy, Food and Agriculture Organization, Kuala Lumpur,
Malaysia.
Levine, J.S., W.R. Cofer, D.R. Cahoon and E.L. Winstead (1995)
Biomass burning: A driver for global change. Environmental
Science and Technology, 29: 120A-125A.
Levine, J.S. (2000) Global biomass burning: A case study of thegaseous and particulate emissions released to the atmosphere
during the 1997 Fires in Kalimantan and Sumatra, Indonesia. In:
J.L. Innes, M. Beniston and M.M. Verstraete, eds., Biomass
Burning and its Inter-relationships with the Climate System, 3,
15-31, Kluwer Academic Publishers, Netherlands.
Office of Natural Resources and Environmental Policy Planning(OEPP) (1990) Inventory 1990: Field Burning of Agriculture
Residue Sector. <www.onep.go.th>
Reid, J.S., R. Koppmann, T.F. Eck and D.P. Eleuterio (2005) A
review of biomass burning emissions part II: intensive physicalproperties of biomass burning particles. Atmospheric Chemical
Physics 5: 799-825.
Seiler, W. and P.J. Crutzen (1980) Estimates of gross and net fluxesof carbon between the biosphere and the atmosphere from biomass burning, Climatic Change, 2: 207-247.
Streets, D.G., K.F. Yarber, J-H. Woo and G.R. Carmichael (2003)
Biomass burning in Asia: Annual and seasonal estimates andatmospheric emissions. Global Biogeochemical Cycles, 17(4):101-119.
Yamasoe, M.A., P. Artaxo, A.H. Miguel and A.G. Allen (2000)
Chemical composition of aerosol particles from direct emissionsof vegetation fires in the Amazon Basin: water soluble species
and trace elements. Atmospheric Environment, 34: 1641-1653.

37

Sébastien BONNET
Dr Sébastien BONNET is a lecturer at the Joint
Graduate School of Energy and Environment(JGSEE) in Thailand where he has been working
for almost a decade. His research interests are
related to sustainability assessment of biomass
resources utilisation and environmental impacts
related to climate change. Dr Sébastien is teaching several courses
including risk assessment and has coordinated the organization of several
international conferences, workshops and seminars in the area of energy
and environment. He is also Assistant Managing Editor of the Journal for
Sustainable Energy and Environment (JSEE).

Savitri GARIVAIT
Savitri GARIVAIT is an Associate Professor ofEnvironmental Technology and Science at the
Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology
Thonburi. She has a Master’s degree in Physical
Chemistry, and PhD in Atmospheric Chemistry
and Physics of the Environment from University of Paris 7, France. Her
research focuses on emissions of aerosols from biomass burning into theatmosphere, with emphasis on their properties related to radiative forcing
and climate change. Her research interests cover various aspects ofatmospheric chemistry and climate change, especially emissions andmitigation options of radiative forcing agents including greenhouse gases
and aerosols from biomass production (agriculture and forestry) andcombustion (agricultural field burning and forest fires) in Southeast Asia.

(Received 1 June 2011, Accepted 22 November 2011)