Mangrove Loss and Growing Coastal Flood Exposure in East Malaysia: A Multi-Decadal Analysis with Sea Level Rise Projections

Mangrove forests provide critical coastal flood protection, yet their ongoing loss in combination with sea level rise creates a compounding exposure dynamic that remains poorly quantified at sub-national scale across Southeast Asia. This study presents the first systematic, multi-decadal analysis of mangrove loss and coastal flood exposure change for the 10 km coastal buffer of East Malaysia (Sabah and Sarawak), covering 1996 to 2020 and projecting forward to 2050 under a structured scenario matrix. Drawing on five openly available global datasets — the Global Mangrove Watch v3.0, Copernicus GLO-30 digital elevation model, WorldPop 2020 population grid, GADM v4.1 administrative boundaries, and IPCC AR6 sea level projections — and a reproducible Python-based workflow, the study quantifies mangrove extent change, hydrologically-connected inundation zones at five elevation thresholds, flood exposure attributable to historical loss, and population exposure under six combined mangrove loss and sea level rise scenarios. Net mangrove loss of 46.34 km² (−1.14%) was recorded over the study period, masking a gross loss of 114.06 km². Four spatial hotspots were identified: the Rajang Delta, SW Sarawak coast, Menumbok Forest Reserve and Kinabatangan coast. Historical mangrove loss exposed an additional 43.79 to 52.14 km² of coastline to inundation, affecting approximately 10,200 to 12,730 people. Scenario projections to 2050 demonstrate that mangrove management trajectory exerts a substantially greater influence on future flood exposure than the choice of emissions scenario, with the spread across mangrove loss scenarios (~31 km², ~13,400 people) exceeding the SSP2-4.5 to SSP5-8.5 spread by more than an order of magnitude. These findings underscore the value of mangrove conservation as a near-term, nature-based coastal adaptation measure in the Indo-Pacific region.Keywords: Mangrove loss; coastal flood exposure; sea level rise; East Malaysia; nature-based adaptation; inundation modelling; blue carbonArticle highlights: Net mangrove loss of 46.34 km² recorded in East Malaysia's coastal buffer, 1996–2020 Four loss hotspots identified including the Rajang Delta and Menumbok Forest Reserve Historical loss exposed 43.79–52.14 km² of additional coastline to inundation risk Mangrove management trajectory dominates over SLR scenario choice at 2050 horizon Reproducible open-source workflow transferable to other Indo-Pacific mangrove coastlines