key word is peatlands. Peat is an accumulation of decayed vegetation accumulated in the swamp forests of Sumatra and Borneo. In the last ten years the land-rush for oil palm and pulp wood plantations targeted the peat-forests, that has been logged, drained and converted into plantations. But the nature is taking it revenge: once drained, peat oxidizes, and while releasing huge amounts of carbon in the atmosphere, it simply disappears. The soil level drops down, a phenomena that is called o “soil subsidence”. As a result, extensive regions of South East Asia will be irreversibly flooded by fresh or even by salty water.

The loss of agricultural production in such large areas of land will have severe socio-economic consequences, and radical changes to land use policies on peatlands in the region are needed in order to avoid this. The solution lies in protecting remaining natural peat swamp forests and restoring degraded areas. This can only be done through cooperation with local communities and industry and in combination with sustainable economic development.

Subsidence is the lowering of the soil surface as the result of compaction, consolidation and loss of volume due to deforestation, drainage, oxidation and erosion. Peat soils are made up of 10% accumulated organic material (carbon) and 90% water. When the water is removed by drainage, the carbon in the peat soil is exposed to the air, turns into CO2 and is emitted into the atmosphere. The process continues as long as drainage continues and until all peat above the drainage level is lost.
 
A new study commissioned by Wetlands International and carried out by Deltares shows that under current trends vast areas in Indonesia and Malaysia will be frequently flooded by the middle of this century. The study analysed an area of 850,000 hectares located along the Rajang delta on the coast of Sarawak, a Malaysian state in Borneo.

From 2000 to 2014, the cover of industrial oil palm plantations increased from 6% to 47%, while the area of swamp forest decreased from 56% to less than 16%. The remaining area is also mostly drained, meaning that the entire area is now subsiding. The model suggests that in 25 years 42% of oil palm plantations in the area will be at risk of flooding. In 50 years that percentage increases to 56% and in 100 years to 82%. You can download the report and watch the flood simulation here. 

In Sumatra alone, subsidence will affect thousands of kilometres of coastline, or millions of hectares of lowlands along the eastern coast, comparable to over 5 times the size of the Netherlands or almost twice the size of Java. In the Borneo provinces of Indonesia, Kalimantan, millions of hectares will similarly experience increased and prolonged flooding if peatlands continue to be drained for oil palm and Acacia (for pulp wood) plantations.