Hydrological changes and vertical crustal deformation in south India: Inference from GRACE, GPS and absolute gravity data

Monsoon rainfall over Indian subcontinent causes large hydrological changes that deform the earth on varied time scale. The seasonal hydrological mass changes are in the range of 20–50 cm of equivalent water height over southern India, which causes vertical deformation of 1–2 cm. We compare the deformation computed from GRACE mass signal with that of height changes from continuous GPS data from two locations in south India and find that the amplitude and phases of seasonal vertical deformation derived from both (GPS and GRACE) are consistent, indicating that hydrological effects are major cause of periodic deformation in the region. This supports the earlier deduction that GRACE data can be utilized to remove hydrological effects from GPS data. High precision absolute gravity values measured near the GPS location and groundwater levels measured in the boreholes corroborate the space based observations of hydrological changes and vertical deformation. GPS and GRACE data also indicate inter-annual variation caused due to rainfall variability, signifying that hydrological effects must be removed before deriving any long term vertical deformation trend.