Application of Spatial Model the Contribution of Land Subsidence Caused by Palm Oil Plantations Land Clearing to the Escalating Flood Risk in the Trumon Area, South Aceh Regency, Indonesia

Abstract

The Trumon watershed one of critical watershed in Aceh Province had an increase in historical flood episodes during the past 25 years. This is consistent with the expansion of oil palm plantations within the 53,653 Ha watershed basin dominated by peatlands. According to earlier research, changes in land use in peatland regions may cause subsidence. This research looks at the connection between flood events and the subsidence of ground caused by oil palm plantation land clearing. The satellite imagery interpretation reveals a remarkable land use change of previously 5091.25 Ha peatland forest observed in 1995, to become a 13,753.43 Ha palm oil plantation in 2021. From DEMs analysis, those changes are associated with a subsiding land elevation up to 1.23 m. Despite being less than 20% of the watershed area, the land subsidence effect striking change in the watershed boundary, i.e., from only 53,653 Ha to 786,675 Ha which led to an increase in flood inundation from 3,443.04 Ha to 47,924.92 Ha. and flood depth from 0.5 – 1.0 m, to up to 4.0 m. This current situation has made the Trumon area subjected to frequent floods, i.e., from a five-year return period to become an annual event.