Control of non-linear vertical land motion on future sea-level projections across the eastern Indian Ocean

Sea-level change has garnered significant interest, particularly in recent decades, and is becoming of undeniable concern for numerous stakeholders and communities globally. Vertical land motion contributes to local sea-level change but its causes and rates vary widely. Whilst long term, large scale isostatic adjustment is predictable, short term, local non-linear changes (e.g., subsidence via groundwater extraction, or active tectonics) remain unaccounted for in current sea-level projections. In the eastern Indian Ocean, large uncertainties in VLM remain, which we consider an effect of non-linear behaviour and we assess to improve predictability. Owing to a lack of long term VLM data in the region, we test approaches combining tide gauges and satellite altimetry to derive 30-year VLM time series. We validate the approach using 20 TGs co-located with GNSS measurements of VLM. We separate the signal into linear and non-linear components and demonstrate, for example locations, the effect of propagating non-linear VLM into local sea-level projections.