Wetlands International warns for massive land subsidence in Rajang river delta, East Malaysia
Agricultural production in vast regions of South East Asia will be lost in the coming decades as a result of flooding of extensive lowland landscapes due to unsustainable development and management of peat soils.
According to Dutch-based organisation Wetlands International about 82 percent of the Rajang river delta in Sarawak, East Malaysia, will be irreversibly flooded within 100 years and substantial areas are already experiencing drainage problems.
Wetlands International commissioned a study on the subsidance of oil palm plantations in the Rajang delta peatland. The study has been executed by research institute Deltares.Study area of the Rajang river delta in Sarawak, East Malaysia.
Conservation and sustainable management of peatlands
The study suggests that extensive drainage of peatlands for oil palm cultivation in the Rajang river delta results in such massive land subsidence that this will lead to extensive and devastating flooding incidents in the coming decades.
The drainage problems will increasingly impact local communities, the economy and biodiversity and will develop over time into disastrous proportions unless land-use on the region’s peatlands is radically changed.
Therefore Wetlands International calls for conservation and sustainable management of peatlands in South East Asia.
Permanent flooded in hundred years
The study analysed an area of 850,000 hectares of coastal peatlands in Sarawak, and produced a model which demonstrates that the nature of flooding will become more serious and permanent, and in 100 years 82 percent of the peatlands will be affected.
Such extensive flooding is due to massive conversion of peat swamp forests to agriculture, mainly oil palm plantations: currently only 16 percent of Sarawak’s natural peat forests remain. These valuable crops require drainage in order to be profitable.Models show that drainage-based activities will lead to subsidence with large areas to flood at high tides (dark blue) and areas that cannot be drained freely anymore (light blue) by 2109.
Adversely impact of drainage-based activities
"The results of the model clearly shows the need for a radical change in peatland landuse not only in Sarawak but in all peat landscapes in the region", said Lee Shin Shin, senior technical officer of Wetlands International in Malaysia.
"Current trends whereby vast areas of peatlands are opened up for drainage-based activities will render these areas unproductive and useless and this will adversely impact communities, industries and biodiversity that rely on such areas for their very survival and existence", warns Shin Shin.
Peat soils are made up of only 10 percent accumulated organic material (carbon). The remaining 90 percent is water. When water is drained from the peat soil, the carbon in the peat soil is turned into CO2 and emitted into the atmosphere causing climate change.
This carbon loss reduces the peat volume and thus causes the peat soil to subside. This process continues as long as drainage is continued and until the soil surface reaches sea or river levels constraining the outflow of water and thus leading to flooding.
Same pattern in Indonesia
"The study results are very relevant to Indonesia as well, where we observe the same patterns of peat swamp forest conversion, drainage and expansion of oil palm and Acacia for pulp wood plantations", said Nyoman Suryadiputra, director of Wetlands International in Indonesia.
"Thousands of square kilometres in Sumatra and Kalimantan may become flooded in the same way as the Rajang delta, affecting millions of people who depend on these areas for their livelihoods”, adds Suryadiputra.Six villages flooded in the Matu-Daro district in January 2011 after heavy downpour.
No measures to stop subsidence
"Highly developed countries or regions in temperate areas, such as the Netherlands, cope with soil subsidence by building dykes and pump-operated drainage systems, but this is impossible in Malaysia or Indonesia”, explained Marcel Silvius, programme head for climate smart land use at Wetlands International.
Silvius: "The predominantly rural economy along thousands of kilometres of coastline and rivers, combined with the intense tropical rainfall makes it economically and practically impossible to implement such costly water management measures in the Southeast Asian region".
According to Wetlands International, governments and industry should therefore immediately stop the conversion of remaining peat forests to agricultural or other use, and actively promote peatland conservation and restoration. The organisation believes there are many crops that can be cultivated on peatlands without drainage.
This news item was originally published on the website of Wetlands International.
Download the full report by Deltares (as a pdf-file): Flooding projections from elevation and subsidence models for oil palm plantations in the Rajang Delta peatlands, Sarawak, Malaysia
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