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This is a copy of paper submitted to Ecosystems. Please do not quote, copy, share,

print, multiply or distribute, except within the STRP group on Wetlands and

Climate Change.

Current and future CO2 emissions from drained peatlands in

Southeast Asia

Shortened title (<45 characters):

CO2 emissions from drained peat in Southeast Asia

Authors:

Aljosja Hooijer (WL | Delft Hydraulics, PO Box 177, 2600 MH Delft, The Netherlands;

[email protected], Tel +31 15 2858770)

Henk Wösten (Alterra, Wageningen University and Research Centre, PO Box 47, 6700 AA

Wageningen, The Netherlands)

Marcel Silvius (Wetlands International, PO Box 471, 6700 AL Wageningen, The Netherlands)

Susan Page (Department of Geography, University of Leicester, University Road, Leicester, LE1 7RH,

United Kingdom)

Jaap Kwadijk (WL | Delft Hydraulics, PO Box 177, 2600 MH Delft, The Netherlands)

Josep G. Canadell (Global Carbon Project, CSIRO Marine and Atmospheric Research, GPO Box 3023,

Canberra, ACT 2601, Australia)

Abstract (250 words max)


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Forested tropical peatlands in Southeast Asia store at least 42,000 Million metric tonnes of soil carbon.

Human activity and climate change threatens the stability of this large pool which has been rapidly

decreasing over the last few decades due to deforestation, drainage and fire. In this paper we investigate

the emission due to drainage for agricultural and silvicultural development which has dominated, and is

expected to dominate, the perturbation of the carbon balance in this part of the world. Present and

future emissions from drained peatlands were quantified using data on peat extent and depth, present

and projected land use, water management practice and decomposition rates. Of the 27.1 million

hectares of peatland in Southeast Asia, 12.9 million hectares are currently deforested and mostly

drained; this area is rapidly increasing. Current carbon dioxide (CO2) emissions caused by

decomposition of drained peatlands alone, not including the effect of peatland fires, are 632 Mt y-1

(range: 355-855 Mt y-1

). Based on a ‘business as usual’ scenario of land use change, the magnitude of

emissions may peak at 745 Mt y-1

in coming decades unless land management practices and peatland

development plans are significantly changed, and will continue throughout the 21st century. Peatland

drainage in Southeast Asia is a globally significant source of CO2 emissions and a major obstacle to

meeting the aim of stabilizing global greenhouse gas emissions. It is therefore recommended that

international action is taken to help Southeast Asian countries to better conserve their peat resources

through both forest conservation and water management improvements aiming to restore high water

tables.

Key words

peatlands, peat decomposition, water management, drainage, subsidence, CO2 emission, climate change

INTRODUCTION

Peat deposits consist of plant remains (some 10% by weight) and water, accumulated in permanently

waterlogged and acidic conditions. Peatlands are, more than any other ecosystem, the result of a fine

balance between hydrology, ecology and landscape morphology (Page and others 1999). A change in

one of these three system components will inevitably lead to a change in the other components and in

peat accumulation rate. It follows that human intervention will have a major impact on the peatland

hydrological system, and that water management must be carefully adapted to minimize this impact

(Hooijer 2005a; Wösten and others 2006a).


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Peatlands cover 27.1 Million hectares in Southeast Asia according to the data used in this study

(Wetlands International 2003, 2004; FAO 2004). Over 22.5 Million hectares (83%) of this are in

Indonesia, where peatlands make up 12% of the land area, with a further 2 Million hectares in Malaysia

and 2.6 Million hectares in Papua New Guinea. Peat thicknesses range from less than 1 to up to 20

metres (Page and others 2002); a substantial fraction of peatlands is over 4 metres thick (at least 17% in

Indonesia). These numbers yield a total carbon store in Southeast Asian peatlands of at least 42,000

Million tonnes (assuming a carbon content of 60 kg m-3).

Peatlands in Southeast Asia are now rapidly being deforested, drained and burnt for development of

agriculture (including oil palm and timber plantations) and for logging. These developments cause

major changes in the peatland hydrology, and as a result the carbon stored is now being released to the

Earth’s atmosphere through two mechanisms:

• Drainage of peatlands leads to aeration of the peat soil and hence to aerobic decomposition of peat

material that results in a sustained release of CO2 as illustrated in Figure 1.

• Fires in degraded and often drained peatlands result in further and abrupt release of CO2.

(FIGURE 1 NEAR HERE)

We analyzed present and ‘business as usual’ future CO2 emissions in Southeast Asia caused by

peatland drainage, not including the effects of peatland fires. Although the link between peatland

development and CO2 emissions is well-known from a vast body of work in Northern Hemisphere

peatlands, and research has been published into CO2 emissions due to deforestation in tropical areas

(Santilli and others 2005) and from fires in Southeast Asian peatlands specifically (Page and others

2002), little is known on the significance of sustained atmospheric C sources due to drainage in the

deep tropical peatlands.

From national and regional perspectives, policy makers are insufficiently aware of the global

implications of peatland drainage. This makes it difficult to establish fundamental connections between


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the agendas of development and climate change that would support actions consistent with long term

sustainable development (Gullison and others 2007).

In this paper we provide a comprehensive regional analysis of CO2 emissions from drained peatlands in

Southeast Asia pertaining to lowland peatlands in Indonesia, Malaysia, Papua New Guinea and Brunei.

The goal of the study is twofold: to improve understanding of the global spatial attribution of sources

of atmospheric carbon by providing estimates of carbon emissions from Southeast Asia’s peatlands,

and to provide information to national and regional policy makers and local peatland managers working

towards a better integration of the development and climate change agendas.

DATA AND CALCULATION METHODS

In order to estimate current and future CO2 emissions from drained peatlands, the following

information was obtained: (A) where and how thick the peatlands are, (B) where and how they are

drained, (C) what further drainage developments can be expected, (D) how much CO2 emission is

caused by drainage to a certain depth, and (E) how much peat carbon is available for oxidation i.e. how

long emission will continue before the peat carbon stock is depleted. The required information is

addressed in the following steps (for further details on methodologies and data sources see Hooijer and

others 2006).

(A) Peatland distribution and thickness. A peatland distribution map (Figure 2) was derived from

data provided by Wetlands International for the Indonesian islands of Sumatra and Kalimantan

(Wetlands International 2003, 2004). For the remaining areas, the Digital Soil Map of the World from

the Food and Agriculture Organization (2004) was used to determine peat percentage in soil classes.

Peat thickness data for Sumatra, Kalimantan and Papua (Indonesia) were obtained from Wetlands

International. Average peat thicknesses for Malaysia, Brunei and Papua New Guinea were

conservatively estimated on the basis of thicknesses in Indonesia (Figure 3). For the purpose of this

study, we excluded smaller peatland areas found in other Southeast Asian countries which are less

studied and represent only a small fraction of the total area and carbon volume. Peatlands over 300m

above sea level were also excluded for the same reasons.


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(FIGURE 2, 3 NEAR HERE)

(B) Distribution of drained peatlands in the year 2000. A drained area map for the year 2000 was

derived from a global land cover map, GLC 2000 (Bartholomé and Belward 2005). This dataset has a

1km resolution and is based on a classification of SPOT VEGETATION satellite images for the year

2000. The 16 land cover categories of GLC 2000 were divided into four drainage classes: ‘certainly

drained if peatland’ (cropland), ‘probably drained’ (mosaics of cropland and other land uses), ‘possibly

drained’ (shrubland and burnt areas) and ‘probably not drained’ (natural vegetation). Cells were

accordingly assigned to drained area classes (by fraction of area) as shown in Table 2. Drainage depths

for different land uses were estimated from field measurements (Table 2).

Areas of peatland within each drainage class were determined by the following geographic analysis

units using the Arc-GIS package: Provinces (in Indonesia), States and Countries (outside Indonesia).

The results were then organized by these geographic units and further calculations were performed

using this information (Table 1 provides a summary),

(TABLE 1, 2 NEAR HERE)

(C) Historical and future trends in peatland drainage. Historical trends of land use, and therefore of

drained area, were derived from changes in forest area between 1985 (FWI/GFW 2002) and 2000

(GLC 2000 data), as shown in Table 1. Overall deforestation rate in peatlands over this period was

found to be 1.3%/yr. An independent analysis of forest cover change between 2000 and 2006 for most

of Southeast Asia (reported in Hooijer and others 2006) shows that deforestation in peatlands continues

at an unchanged rate since 2000. In a ‘business as usual’ scenario, estimates of drained peatland area in

2006 and in future decades are therefore based on unchanged projection of trends over 1985-2000, by

Province (in Indonesia), State and Country (outside Indonesia). Rates of land use change within the

deforested area, as the deforested area increases, were determined using relations derived from relative

areas on peatland of ‘cropland’, ‘mosaic cropland + shrubland’ and ‘shrubland’ within deforested areas

in Indonesian Provinces in the year 2000 (Figure 4).


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(D) Relation between drainage depth and CO2 emissions. The relation between drainage depth and

CO2 emissions was based on findings by Wösten and Ritzema (2001), who propose that drainage in

agricultural peatlands in Malaysia results in a subsidence rate of 1 cm y-1

and CO2 emissions of 13

tonnes ha y-1

for every 10 cm of water table drawdown, on the basis of data on subsidence and soil

characteristics in drained peatlands. After comparison with findings of a number of gas flux studies in

drained peatlands in Southeast Asia (e.g., Ali and others 2006; Hadi and others 2006; Jauhiainen and

others 2005), it was estimated that every 10 cm water table drawdown results in 9.1 t CO2 ha y-1

(Hooijer and others 2006). This relation needs further development, as in reality it is non-linear and

dependent on land cover as well as drainage depth, but it is considered the best estimate now available

for drainage depths between 0.5 m and 1m, which is the most common drainage depth range in the

study region. It should be noted that CO2 emissions from drained peatlands, on a unit area basis and at

the same drainage depth, are far higher in the tropics than in temperate and boreal areas, because the

rate of aerobic decomposition is strongly influenced by temperature (Wösten and others 1997).

(E) Carbon content. Carbon content of Southeast Asian peat was assumed to be 60 kg m-3

(Wösten

and Ritzema 2001). This figure was applied to all areas.

RESULTS

Using the data and relations described above, the CO2 emission from all geographic units was

calculated as follows:

CO2 emission = LU_Area * D_Area * D_Depth * CO2_1m [t/y]

Where:

LU_Area = peatland area with specific land use [ha]

D_Area = drained area within peatland area with specific land use [fraction]

D_Depth = drainage depth in peatland area with specific land use [m]


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CO2_1m = CO2 emission at a drainage depth of 1m = 91 [t/ha/y]

It follows that a peatland area drained fully to 0.95 m on average (considered ‘most likely’ in

plantations and other large-scale ‘cropland’ areas; Table 2) will emit 86 t CO2 ha y-1

. A peatland area

drained to 0.6 m depth (typical in small-scale agricultural areas, i.e. ‘mosaic cropland and shrubland’)

for most of its area (88%, Table 2) will emit 48 t CO2 ha y-1

. An area drained to 0.33 m for half its area

(considered likely for ‘shrubland’, i.e., recently deforested areas, and burnt and degraded agricultural

areas; see Table 2) will emit 15 t CO2 ha y-1. Following this calculation method, ‘minimum’, ‘most

likely’ and ‘maximum’ emission rates for 3 land use types (‘cropland’, ‘mosaic cropland and

shrubland’, and ‘shrubland’) were calculated by varying drained area and drainage depth in each land

use type (Table 2). The overall range of emissions calculated was between 6 and 100 t CO2 ha y-1

.

Values in this range are also reported for several gas flux studies in experimental plots (Ali and others

2006; Furukawa and others 2006; Hadi and others 2006; Jauhiainen and others 2006).

Projections based on land cover data for 1985 and 2000 indicate that about 47% of peatlands in

Southeast Asia, or 12.9 Million hectares, were deforested by 2006. Projected rates of land use change

within deforested areas in Southeast Asia over the same period suggest that 17% of this land is now

affected by intensive drainage for large-scale agriculture (GLC 2000 class ‘cropland’), 67% is affected

by moderately intensive drainage for small-scale agriculture (‘mosaic cropland and shrubland’), and

16% is affected by unmanaged drainage in degraded non-agricultural areas (‘shrubland’). This results

in an estimated total drained peatland area of 11.1 Million hectares (range: 9.5 - 12.7).

By multiplying CO2 emissions per hectare of each land use type with the total area in that land use

class, we estimated that present CO2 emissions from drained peatlands are 632 Mt y-1

(range: 355 -

855). If current rates and practices of peatland development and degradation continue, CO2 emissions

will peak at 745 Mt y-1

in 2015, followed by a steady decline over many decades when increasingly

thicker peat deposits become depleted (Figure 5). In the maximum drainage scenario, projected

emissions peak at 936 Mt y-1

by 2010. After reaching a maximum, CO2 emissions will steadily decline

while ever deeper peat deposits are depleted, but they will be significant throughout this century. By


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2030, total projected emissions are 514 Mt y-1

if peatland drainage continues unmitigated; by 2070 they

would still be 236 Mt y-1

Cumulative CO2 emissions from all peatlands in Southeast Asia were calculated at 9,700 Mt (range:

5,300-13,700) by 2006, 25,900 Mt (range: 17,200-31,000) by 2030 and 37,300 Mt (range: 28,900-

39,900) by 2070. Indonesia with its vast peat resources is the single largest CO2 emitter from drained

peatlands, responsible for 82% of Southeast Asian emissions in 2006, with Sumatra being the largest

emitter closely followed by Kalimantan.


DISCUSSION

Current CO2 emissions from drained peatlands in Southeast Asia (excluding emissions from fires) are

estimated to be 632 Mt y-1 year (range: 355 – 855). This is equivalent to 2.4% of the 26.4 Billion metric

tonnes of CO2 y-1

of global emissions from fossil fuel combustion during the period 2000-2005 (IPCC

2007). In a ‘business as usual’ scenario that extends current drainage trends into the future, emissions

from drainage will further increase in coming decades before starting to decrease due to depletion of

shallower peat resources. Emissions from the deeper peatlands will continue throughout this century.

Further CO2 emissions from degraded and drained peatlands are associated with peatland fires, which

during non- ENSO (El Niño-Southern Oscillation) years can be of similar magnitude to those from

decomposition and several times larger during ENSO years. Page and others (2002) estimated that

emissions from peatland fires in Indonesia during the 1997 ENSO were 3000 Mt CO2 (range: 1800 –

8800), equivalent to 14% of global emissions from fossil fuel combustion. An assessment on the basis

of this figure and of annual ‘fire hotspot’ counts in Borneo over the period 1997-2006 estimated an

average emission of 1400 Mt CO2 y-1

from peatland fires in Southeast Asia (Hooijer and others 2006).

This brings the total CO2 emissions to about 2000 Mt y-1

or equivalent to 7.6% of current global CO2

emissions from the combustion of fossil fuel.


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One final component needs to be computed to understand the full impact of drainage and loss of forest

in peatlands on the net carbon balance of tropical swamp forests: the loss of carbon sink capacity.

Peatlands in their natural state store carbon at an average rate in the order of 84 g C m2 y-1 (Page and

others 2004; Rieley and others 1996). Loss of all peatland forest in Southeast Asia means a loss of CO2

uptake capacity of 84 Mt y-1

. The present loss of peatland forest in SE Asia has already reduced global

CO2 uptake capacity by at least 40 Mt y-1

.

The emissions from drained peatlands in Southeast Asia, even without including the effect of fires,

contribute more to atmospheric greenhouse gas emissions than industrialized nations like Germany or

the United Kingdom produce by the combustion of fossil fuels (804 and 558 Mt y-1

respectively, CO2

emission in 2003, CDIAC 2007). Emissions from drained peatlands are produced on what is effectively

only less than 0.1% of the global land area. Deforested and drained peatlands in Southeast Asia are

major Earth system hotspots for carbon emissions rivalled by few, if any, CO2 emission sources in

terms of emission per unit area.

Although deforestation and drainage are the current dominant factors driving carbon emissions from

peatlands, future climate change will add further pressure to peat ecosystems and most likely enhance

carbon emissions. An analysis of climate projections contributing to the IPCC Fourth Assessment show

that 7 out of 11 models predicted that by the end of this century there will be a decrease of rainfall

during the dry seasons in a number of regions of Southeast Asia (Li and others 2007). Moreover, 9 out

of 11 models predict greater interannual variation in dry season rainfall. These changes are strongest

and most consistent across the models for southern Sumatra and Borneo, where most peatland in

Indonesia occurs. Decreased rainfall during the dry season will result in lower water tables exposing

larger carbon stocks to suitable aerobic conditions for decomposition, and hence larger CO2 emissions.

A further potential effect of climate change on CO2 emissions from peatlands is supported by field

studies in southern Sumatra which shows strong positive influence of increased soil temperature on

CO2 emission (Ali and others 2006).

The carbon consequences of recent El Niño years are a good window into the future to understand the

likely positive feedbacks of climate change (lower rainfall and higher air temperatures) and continued


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land use change (deforestation and drainage). Particularly vulnerable are degraded areas where the

natural self-regulating hydrological systems have been lost and no artificial water level control system

has been implemented.

Sustainability of peatland drainage and environmental consequences

Drainage of peatlands in Southeast Asia often does not bring sustainable agricultural or economic

development. Most peatlands are located at or close to the Sea coast, with surface elevations only a few

metres above Sea level and the mineral subsoil often below the gravity drainage base, so continued

subsidence of the drained peat surface (caused by compaction, aerobic decomposition and fires) will

ultimately cause the peat area to become undrainable, often within decades of the initial excavation of

canals (Hooijer 2005b). Inundation frequency will increase and areas below the high-water level will

be affected by salt water intrusion. As the cost involved in non-gravity drainage (i.e. water pumping) is

usually too high to be economical in this region, agricultural productivity will decline. Another cause

of reduced productivity and sometimes abandonment of coastal drained peatland areas is when the

mineral subsoil is aerated and acid sulphate problems develop, as are common along many coastlines in

Southeast Asia.

Furthermore, an array of environmental and socio-economic impacts occurs as a result of deforestation

and drainage. Peat fires cause haze (smoke) problems which affect public health and economy (e.g.

transport, tourism) in much of the Southeast Asian region. Loss and degradation of conservation forest

affects biodiversity and natural timber production in the longer term. Flooding problems are reported,

but not quantified, downstream of drained and burnt peatland areas such as the former Mega Rice

Project in Indonesia (Wösten and others 2006b).

Perspectives for sustainable peatland management

Given the high CO2 emissions, per unit area and in absolute terms, and the relatively small area

involved from a global perspective, it seems that emissions from peatland deforestation and

mismanagement in Southeast Asia are both important enough to require international action and

‘compact’ enough for mitigation policies to be effective. Carbon emissions and other negative effects

resulting from unsustainable peatland management can be reduced, particularly in Indonesia, if


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international support is provided to adopt and implement a land development policy based on the

following three principles:

1. Forest conservation and drainage avoidance in remaining peat swamp forests.

2. Where possible, rehabilitation of degraded peatlands through restoration of natural hydrological

systems and of forest cover.

3. Raised water levels through improved water management in existing plantations in peatlands,

embedded in water management master plans for peatland areas.

Improved water management is the basis of conservation of peat resources in Southeast Asia. Current

management priority in most agricultural areas in peatlands is to prevent high water levels in the wet

season, and in many cases to maintain boat access along canals during the dry season. However the

excessive drainage capacity maintained in such a system, without further mitigative measures, also

leads to a drop in water table depth below the peat surface by more than 1 or often even more than 2

metres during the dry season in many drained peatland areas. Such low water levels can often be

prevented through improved water management which stabilizes water levels by adjusting drainage

capacity to meet seasonal requirements (Wösten and Ritzema 2001, Hooijer 2005b). However such

management is more costly and requires specific technical knowledge that is often not available

locally.

One important issue that was not addressed in the analysis, but which should be taken into account in

peatland water management, is the fact that drainage affects peatlands over large distances, well

beyond the 1km cell resolution used in the analysis. This means that a single road or small plantation in

peatland will cause peat surface subsidence, CO2 emission and enhanced fire risk over much larger

areas. It also implies that exclusion from development of peat deposits over 3 metres thick as is now

the law in Indonesia (although rarely enforced), is of limited practical relevance as in time most peat

deposits will be less than 3 metres thick through progressive subsidence following drainage, and would

become available for development. It seems more practical and realistic to recognize that peat ‘domes’

are self-contained hydrological units that may be kilometres or tens of kilometres accross; interventions

in part of the unit will in the long term affect the entire unit. Single peat domes are therefore best

managed under a single water management regime or at least a water management regime that aims to


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maintain the hydrological integrity of most of the unit. A decision may be made to develop a peat dome

for agriculture/silviculture, or to conserve it as an undrained forest area, but combining development

and conservation can often not be sustainable unless major and costly water management measures are

taken and maintained in buffer zones that are a minimum width of several kilometres.

Finally, an issue which deserves further attention is the fact that development of oil palm (and pulp

wood, for paper production) plantations is a major cause of peatland deforestation and drainage in

Southeast Asia. The global demand for palm oil is growing fast, and according to research by the

Indonesian Ministry of Forestry and the European Union (Sargeant 2001) much of the 300,000 ha

additional oil palm plantation development required annually will take place in Indonesia’s peatlands.

Some 25% of palm oil is already produced on peatlands and this percentage is expected to rise (Hooijer

and others 2006). A major driver of the increasing demand for palm oil is its use as a biofuel in the

European and other markets, with the aim of reducing global CO2 emissions to meet targets under the

Kyoto Protocol. We suggest that the CO2 emission from drained peatlands should be taken into account

when considering use of palm oil as a biofuel.

Future research for reduced uncertainties

In this section we discuss the main uncertainties of this analysis and identify knowledge gaps with the

aim to guide future research priorities.

• The thickness of many peatlands in Indonesia is not very well known. Peat thicknesses tend to be

greatest in the central parts of the inaccessible and often vast dome-shaped peat bodies, often tens

of kilometres across. Many of the measurements on peat thicknesses are nearer to the fringes. For

this study no data was available on thickness of peatlands in Malaysia and Papua New Guinea;

conservative estimates were used. Overall, this is likely to result in underestimation of peat

thickness and the size of the carbon stock. With the data used, the original carbon stock in

Southeast Asia is calculated at 42,000 Mt; this is at the low end of published estimates.

• Data on extent and distribution of peatlands can be improved, especially for areas outside of

Kalimantan and Sumatra.

• Carbon content of Southeast Asian peat was assumed to be 60 kg m-3

(Wösten and Ritzema,

2001), while carbon contents up to 90 kg C m-3 have been reported for various peat deposits (e.g.


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Wetlands International 2003, 2004). Assuming higher carbon content would result in higher total

carbon stocks and higher CO2 emissions from peatland drainage.

• Drainage intensity as derived from the GLC 2000 global land cover classification may not always

be accurate, for example in the case of Papua (Indonesia). Here, areas now classified as ‘mosaic

cropland + shrubland’ are known to actually be a savannah-like landscape created by traditional

land management techniques requiring regular burning (Silvius and Taufik 1990). These areas are

generally not ‘drained’ in the normal sense; agriculture often takes place on elevated islands of dug

up mud (from the submerged swamp soil). This may have lead to an overestimate of CO2

emissions from Southeast Asian peatlands, with a maximum of 16% in the unlikely case that

emissions from Papua would actually be negligible.

• The percentage of peatland drained within land use classes was estimated from field work which

naturally did not cover all peatland regions. The percentage of drained peatland may be much

larger than assessed here, as several interventions in the hydrological system are not taken into

account. These are A) log transport canals in forested areas where legal or illegal logging takes

place, and B) the impacts of plantation and roadside drainage over distances of kilometres in

forested areas. Peatland fires also have a draining effect on the remaining forested peatland as they

create depressions in the peat surface. Over 90% of peat swamp forests in Sumatra was already

affected by human interventions in the early 1990s (Silvius and Giesen 1992), so probably only

few peatlands in Sumatra, Kalimantan and Malaysia are not affected by drainage at present.

• Estimated likely drainage depths may be greater than those recommended in existing

management guidelines, but are shallower than depths often observed by the authors in practice.

Drainage depths between 1 and 2 metres are often observed in oil-palm and pulp wood plantations.

In unsuccessful and abandoned plantations such as the ex-Mega Rice Project in Central

Kalimantan (with over 1 million hectares of derelict drained peatland), drainage depths of up to 3

metres are reportedly common in the dry season. The ‘likely’ average drainage depth of 0.95m, as

assumed for plantations and other cropland areas in this assessment, is considered an

underestimate.

• Values for current (2006) land use were based on GLC 2000 data from 2000, as this is the most

up-to-date published and validated land use dataset available for all of Southeast Asia. More recent

land use data would have yielded more accurate results.


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• The ‘business as usual’ land use projection used is a continuation of past trends, so assuming

there will not be major changes on peatland conservation and management strategies. The

projection method for land uses in deforested peatland area limits the area of intensively drained

‘cropland’, including plantations, to 21% of the total peatland area. In reality, the registered area of

palm oil and timber plantation concessions alone, which require very intensive drainage, is already

23% of the peatland area in Indonesia (Hooijer and others 2006). In addition, many plantations and

other agricultural projects are developed outside this concession system. There are expectations

that most of the annual global increase in oil palm plantations, 300,000 ha y-1

for the next 15 or 20

years, will be developed in Indonesia’s peatlands (Sargeant 2001). It is therefore conceivable that

over 50% of peatlands will be intensively drained in a few decades; this would result in a CO2

emission of at least 20% higher than calculated.

• Projections have not taken into account peatland drainability and future management responses.

If peatlands become less productive because of increased flooding due to subsidence, they may be

abandoned and drainage and CO2 emissions may theoretically be reduced. Part of the carbon stock

in peatlands is below the drainage base and may never be oxidized. On the other hand, the current

experience is that abandoned peatlands continue to be drained (as drain blocking is labour

intensive and reduces access), and frequently experience fires in dry years when drainage is not an

issue. The Ex Mega Rice Project area is an example of this.

• Carbon dioxide emission resulting from a specific drainage depth is a very sensitive parameter

in the calculations. Few long-term studies of subsidence rates in drained peatlands in Southeast

Asia have been published. Short-term studies of CO2 emissions are difficult to interpret because A)

CO2 emissions from root respiration must be separated from emissions caused by decomposition,

B) short-term effects (shortly after drainage) must be separated from long-term effects, C) water

table and soil moisture regime are often insufficiently quantified, and D) an unknown part of the

carbon will not be emitted to the atmosphere but will leave the drained peatland in dissolved form

with the drainage water to end up in the Sea (where much of it will likely be oxidized and add to

atmospheric CO2 concentration after all).

• The only form of carbon emission to the atmosphere considered in this assessment is CO2

emission. Methane (CH4) emissions from both undrained and drained peatlands are found to be

modest in comparison with CO2 (Jauhiainen and others 2005; Takashi and others, this volume), but


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may still be significant from a climate perspective given that CH4 is a much stronger greenhouse

gas (23 times stronger in ‘CO2 equivalents’). CH4 emissions in drained peatlands may originate

especially where peat areas are increasingly flooded for prolonged periods, after fires or after

subsidence due to drainage, and reduced conditions are created in the inundated peat soil, but this

process has not been investigated to date.

• Several studies confirm that peatland fires occur mainly in deforested and degraded areas (Siegert

and others 2001; Page and others 2002; Spessa and others, this volume) and are linked to water

table drawdown through drainage. Although this relation has not yet been quantified, CO2

emission from Southeast Asia due to peatland fires is highly uncertain as shown in the discussion

section but can be as much as double the amount of emissions from peat decomposition. Emissions

from peatland fires are not included in the assessment presented here, which results in a significant

uncertainty in CO2 emissions related to peatland drainage.

It is concluded that most remaining uncertainties in CO2 emissions from drained peatlands in Southeast

Asia are greater to the upside than to the downside. This implies that CO2 emissions caused by drainage

in Southeast Asian peatlands are more likely to be above the middle estimate (most likely value, fire

emissions excluded) of 632 Mt y-1

than to be below this value.

It should be noted that most uncertainties pertain to the annual estimates of CO2 emission rather than

the total CO2 emission over the next 50 or 100 years. That is because in the ‘business as usual’ scenario

a lower current emission rate simply means that it will take a few decades longer for the carbon stored

in shallower peat layers to be depleted, but eventually it will still be emitted to the atmosphere.

Further work is required to reduce all the uncertainties listed above. In the short term the greatest

reduction in the overall uncertainty in CO2 emissions from drained peatlands in Southeast Asia may be

achieved through more up-to-date and accurate land use maps. In the longer term the greatest reduction

may be achieved through comprehensive field studies of CO2 emissions (and other carbon balance

components) and subsidence rates in relation to hydrological (especially water level and soil moisture)

and biological (especially vegetation cover) parameters under different water and land management

practices.


16

ACKNOWLEDGEMENTS

The work reported here would not have been possible without the data and other inputs provided by a

great number of people and organizations, especially: Rinus Vis, Marcel Ververs, Rolf van Buren,

Marjolijn Haasnoot (Delft Hydraulics), David Hilbert (CSIRO), Faizal Parish (Global Environment

Centre), Fred Stolle (Global Forest Watch), Florian Siegert (Remote Sensing Solutions), Niels

Wielaard (SarVision), Jyrki Jauhiainen (University of Helsinki). This assessment is a contribution to a

synthesis effort on the vulnerabilities of tropical peatlands carried out under the auspices of the Global

Carbon Project. The original assessment was funded from internal Delft Hydraulics R&D sources,

within the PEAT-CO2 (Peatland CO2 Emission Assessment Tool) research programme.

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19


20

Tables

Table 1 Lowland peatland distribution land use and rate of forest cover loss.

Shrubland + burnt Mosaic: crop+shrub Cropland Forest cover 2000 Forest change

GLC 2000 class: 6 8 total 2 9 total 12 1 4 5 total 1985 85-'00

Lo

wla

nd

pea

tlan

d a

rea

(km

2)

Mo

saic

s &

Sh

rub

Co

ver,

sh

rub

co

mp

on

ent

do

min

an

t, m

ain

ly e

verg

reen

Sh

rub

co

ver,

ma

inly

dec

idu

ou

s, (

Dry

or

bu

rnt)

To

tal

shru

bla

nd

+ b

urn

t

Mo

saic

: T

ree

cove

r a

nd C

rop

lan

d (

incl

.ver

y

deg

rad

ed a

nd

op

en t

ree

cove

r)

Mo

saic

s o

f C

ropla

nd

/ O

ther

na

tura

l ve

g.

(shif

tin

g c

ult

iva

tio

n i

n m

ou

nta

ins)

Tota

l m

ix c

rop

lan

d +

sh

rub

(sm

all

-sca

le

agr.

)

Cu

ltiv

ate

d a

nd

ma

na

ged

, n

on

irr

iga

ted

(mix

ed)

Tre

e co

ver,

bro

ad

lea

ved

, ev

erg

reen

, cl

ose

d

and

clo

sed t

o o

pen

Tre

e co

ver,

reg

ula

rly

flo

od

ed,

Ma

ng

rove

Tre

e co

ver,

reg

ula

rly

flo

oded

, S

wa

mp

To

tal

fore

st (

incl

ud

ing

lo

gg

ed) Global

Forest

Watch /

World

Res. Inst.

Annual

change

over the

period

1985 -

2000

% area % area %area % area % area %area % area % area % area % area % area % area %/y

Total Indonesia 225234 4 2 7 3 24 27 5 27 4 30 61 81 -1.3

Kalimantan 58379 15 4 20 2 17 19 3 30 2 27 58 87 -1.9

Central Kalimantan 30951 19 2 22 2 15 18 3 33 1 24 57 90 -2.2

East Kalimantan 6655 22 19 42 0 9 9 5 29 4 11 44 85 -2.8

West Kalimantan 17569 5 1 7 2 17 19 1 28 3 43 74 92 -1.2

South Kalimantan 3204 15 3 18 6 45 51 14 14 0 4 18 41 -1.6

Sumatra 69317 0 1 1 3 34 37 10 14 2 35 52 78 -1.8

D.I. Aceh 2613 0 0 0 4 28 32 8 37 0 22 59 87 -1.8

North Sumatera 3467 0 2 2 3 39 42 20 20 1 16 36 76 -2.6

Riau 38365 0 1 1 2 24 26 7 14 3 49 66 87 -1.4

Jambi 7076 0 1 1 3 38 40 17 9 0 33 42 67 -1.7

South Sumatera 14015 0 1 2 4 57 61 12 11 1 14 26 66 -2.6

West Sumatera 2096 0 5 5 4 42 46 11 24 0 13 38 69 -2.1

Papua 75543 0 1 2 4 20 25 1 36 9 27 72 80 -0.5

Other Indonesia~ 21995 4 2 7 3 24 27 5 27 4 30 61 81 -1.3

Malaysia 20431 2 1 1 7 32 38 7 36 4 15 53 78* -1.8*

Peninsular 5990 0 1 1 4 47 50 13 37 0 0 37 78* -2.8*

Sabah 1718 8 2 10 3 28 31 17 21 21 2 43 86* -2.9*

Sarawak 12723 2 1 2 9 26 35 4 38 3 23 59 76* -1.1*

Brunei 646 3 1 4 1 9 10 2 39 6 39 84 85* -0.2*

Papua N. Guinea 25680 0 1 1 4 32 35 3 38 5 19 61 80* -1.3*

SE ASIA 271991 4 2 5 4 26 29 5 29 4 28 61 81* -1.3*

~ Land use distribution for 'Other Indonesia' assumed equal to Total Indonesia.

* 1985 forest cover outside Indonesia is estimated.

Table 2 CO2 emission calculation steps and main parameters.

minimum likely maximum

Step A: Drained area Large croplands, including plantations % 100 100 100

(within land use class) Mixed cropland / shrubland: small-scale agriculture % 75 88 100

Shrubland; recently cleared & burnt areas % 25 50 75

Step B: Drainage depth Large croplands, including plantations m 0.80 0.95 1.10

(within land use class) Mixed cropland / shrubland; small-scale agriculture m 0.40 0.60 0.80

Shrubland; recently cleared & burnt areas m 0.25 0.33 0.40

Step C: A relation of 0.91 t/ha/y CO2 emission per cm drainage depth in peatland was used in calculations.

Step D: CO2 emissions Large croplands, including plantations t/ha/y 73 86 100

(calculated from A, B, C) Mixed cropland / shrubland: small-scale agriculture t/ha/y 27 48 73

Shrubland; recently cleared & burnt areas t/ha/y 6 15 27


21

Figures

Figure 1 Schematic illustration of CO2 emission from drained peatlands.

Figure 2 Forest cover on peatland in the year 2000. Note that FAO non-histosol soil classes with 20-40% peat are

not shown, hence the peat extent is greater than shown – e.g. Papua New Guinea has significant peatland cover.

PEAT-CO2 / Delft Hydraulics

Sum

atra

Kalimantan

Sarawak

PapuaIndonesia

Malaysia

Papua New Guinea

Tree cover on peatlandsforest on peatland

deforested peatland

Sources: Peat extent: Wetlands International, FAO Forest extent: GLC 2000

0 500 1000 2000

Kilometres

Clay / sand substrate

Peat dome Natural situation:• Water table close to surface• Peat accumulation from vegetation over thousands of years

Str

eam

ch

an

nel

5 to 50 km

1 to 10 m

Drainage:• Water tables lowered• Peat surface subsidence and CO2

emission starts

Continued drainage:• Decomposition of dry peat: CO2 emission• High fire risk in dry peat:

CO2 emission• Peat surface subsidence due to decomposition and shrinkage

End stage:• Most peat carbon above drainage limit released to the atmosphere,• unless conservation / mitigation measures are taken

PEAT-CO2 / Delft Hydraulics


22

0

2000

4000

6000

8000

0.75 1.5 3 6 10

Peat depth class (m)

Ca

rbo

n s

tore

(M

t)

KalimantanSumatraPapuaMalaysia+BruneiPapua NG

Figure 3 Carbon stored in peatlands, by region and by thickness (source: Wetlands International). Average peat

thickness in Malaysia and Papua N.G. was estimated from peat thickness in Kalimantan and Papua (Indonesia)

respectively.

0

50000

100000

150000

200000

250000

1980 2000 2020 2040 2060 2080 2100

La

nd

use o

n p

ea

tlan

d (k

m2)

Total deforested (lowland) peatland

Large cropland areas (inc. plantations)Mixed cropland and shrubland areas

Recently cleared and burnt areas

Figure 4 Trends and projections of land use change in lowland peatland in SE Asia.


23

Figure 5 Historical, current and projected CO2 emissions from peatlands, as a result of drainage (fires

excluded). The increase in emissions is caused by progressive drainage of an increased peatland area.

The following decrease is caused by peat deposits being depleted, starting with the shallowest peat

deposits that represent the largest peatland area (see Figure 3). The stepwise pattern of this decrease

is explained by the discrete peat thickness data available (0.75m, 1.5m, 3m, 6m, 10m).

0

100

200

300

400

500

600

700

800

900

1980 2000 2020 2040 2060 2080 2100

CO

2 e

mis

sio

n (M

t/y

)

Minimum due to peat decomposition

Likely due to peat decomposition

Maximum due to peat decompositionpresent

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