20th August 2015, a one day workshop was held at the Merdeka Palace Hotel and Suites, Kuching, Sarawak.
Peatlands encompasses 7.45% of the total land area in Malaysia. Only 20% of these peat soil areas remain under forest (peat swamp forest with >70% canopy cover), but these are under serious threat from extensive logging, burning and drainage. Increasing concerns including the loss of biodiversity and CO2 emissions, have been raised over the last decade. Another important environmental impact is peatland subsidence that has received little attention so far in SE Asia, even though this issue is well known in other peatland regions of the world since the 19th century. Unless conservation action and management measurements are taken, our peatlands and the services provided by healthy peat swamp forest like freshwater storage and supply and climate regulation will be lost forever.
We believe that the issue of peatland subsidence and related flood risks will only be taken seriously if policy makers and land-use planners have access to appropriate science-based information and knowledge. Therefore, Wetlands International Malaysia along with Institute of Biodiversity and Environmental Conservation co-organised a stakeholder workshop with the aim of sharing the information and experiences concerning the subsidence and flooding issues occurring based on scientific information gathered and to provide a much broader understanding of the impacts of drainage-based agriculture development on peatland.
Wetlands International commissioned Deltares, a scientific institute with international experience on hydrological management of peatlands, to carry out a case study to provide a scientific assessment of future subsidence and flood risks at the Rajang Delta peatlands in Sarawak; an area that has seen rapid expansion of drainage-based agriculture in recent years. This study report can be found here.
From the study done, it was projected that under three scenarios with an assumed peat soil subsidence rate of 2 cm yr-1, 3.5 cm yr-1 or 5 cm yr-1 respectively, approximately 46%, 69%, and 86% of peatlands in Rajang Delta will likely be subjected to severe flooding in 2059. The study confirms earlier assessments by the Department of Irrigation and Drainage Sarawak (2001). They reported that after the initial two years of drainage under a regulated drainage depth of 0.6m an average subsidence rate of 5 cm yr-1 will occur in Sarawak. Subsidence rates reported for a Johor oil palm plantation were 4.6 cm yr-1 between 14 to 28 years after drainage (Wösten et. al., 1997), and 3.7 cm yr-1 at 11 other locations (DID Malaysia, 1996). Another local study by Mohammed et. al. (2009) showed that on the basis of field monitoring in oil palm plantations on peat with 3 to 4 m in thickness, a subsidence rate stabilises at 4.3 cm yr-1 after 15 years under best management practice with average water depths of 0.4m. Therefore, the subsidence rates applied in the flooding projections in this study are close to most literature values found in local and foreign studies. In addition, in 1982 the Sarawak Department of Agriculture published a map showing the ‘agriculture capability’ stating that all peatland areas are “Land comprising organic soils with such severe limitations that agriculture is not feasible”.
Presentation slides during the workshop and report (Rapid Field Investigation of Flooding in Rajang Delta, Sarawak) are available here.