Hydrological Loading Variability Assessment over Java and Kalimantan from GNSS Data

Global climate change has brought about significant shifts in water availability across various regions, Indonesia included. This study employs GNSS CORS (Continuously Operating Station) data to measure vertical displacements in land surface resulting from hydrological loading. The objective is to analyze the influence of terrestrial water storage (TWS) by isolating and eliminating surface loading sources detected in GNSS data while mitigating uncertainties, noise, and outliers. Along with the GPS data, we utilized GRACE and GLDAS NOAH precipitation data to examine both the spatial and temporal changes in vertical displacement, analyze and correlate these changes. In Kalimantan, vertical movements are generally stable but variable in coastal areas due to tidal effects. In Java, significant deformation occurs in the northern region due to extensive groundwater extraction and local tectonic activity. Stable precipitation on the northern and eastern sides of Kalimantan is corroborated by Terrestrial Water Storage (TWS) values, while in Java, high TWS values are observed near watersheds, correlating with vertical GNSS movements. The correlation between GNSS, precipitation, and TWSA substantiates the presence of seasonal hydrological loading. In Kalimantan, fewer stations have long-term temporal data, resulting in lower correlations between GNSS and TWSA. However, stations such as CRAU exhibit a correlation of -0.5083, indicating subsidence during periods of high TWS.