The impact of vertical land motion and its cascading risks in western Selangor and western Sabah

Abstract

Vertical Land Motion (VLM) can be observed due to natural and anthropogenic drivers. For a downward VLM or subsidence, it can cause an increase in the relative sea level, without actual sea level rises, and its cascading impacts includes coastal inundation, erosion, and saline intrusion. However, understanding the impact of this motion on coastal areas is elusive. This study focused on the distribution of vertical land motion in western Selangor and western Sabah to assess the impact of subsidence and inundation patterns. The study assessed temporal shoreline change their implications, and recommended measures to build long-term measures. Vertical land motion was analysed using two main time-series techniques; Small Baseline Subset (SBAS) and Stanford Method for Persistent Scatterers (StaMPS), which covered the period between 2015 and 2023. The D-InSAR approach was also integrated for short-term changes, such as the 4th June 2015 and 8th March 2018 earthquake events. Temporal shoreline change was determined using Endpoint Rate (EPR) and Linear Regression (LRR) analysis for the duration between 1973 and 2023 for shoreline change. Susceptibility modelling was conducted using the weighted overlay technique to delineate areas at risks of subsidence and flood inundation and identify measures to build resilience. The investigation revealed that Western Selangor had an average of 13.3 mm/yr of subsidence, while western Sabah showed a 22.5 mm/yr change, whereas the D-InSAR approach showed minor subsidence development around the epicenters. The shoreline analysis revealed an average of -8.56 m/yr of erosion rate for Western Selangor and a significantly lower rate of -1.91 m/yr for western Sabah. Similarly, the accretion rate was estimated to be around 6.86 m/yr for the former, while the latter showed an average of 4.32 m/yr. However, western Sabah has higher adverse implications in comparison to Western Selangor. The susceptibility modelling shows, for western Sabah, the Kota Kinabalu district covers a total area exposed to flood at 6,849 ha, whereas the subsidence exceeds 50% of the built areas. In the Western Selangor comprises two districts. The Klang district was the most affected with an estimated coverage of 24,220 ha and 15,172 ha exposed to flooding and subsidence. The Kuala Selangor district was the least affected, with flood and subsidence estimated at around 7,768 ha and 4,448 ha respectively. This study proposes detailed risk assessment within susceptible areas, including implementation of measures such as early warning systems and community preparedness programs. Collaborative effort between stakeholders is necessary to build resilience and maintain sustainable economic growth.