Can't comment on the specific contents of the linked research paper, but just a note that space-based measurements of subsidence have become a lot more routine

Can't comment on the specific contents of the linked research paper, but just a note that space-based measurements of subsidence have become a lot more routine with the development of Interferometric SAR (InSAR). You can get spatial maps of subsidence using the ~monthly/weekly overpasses of the radar, to ~several cm accuracy. It works better over some terrains than others. People aren't wired to notice subsidence, which has meant that large changes due to groundwater pumping and oil/gas extraction have gone "under the radar", and that's changing ;-). Large subsidence can cause problems including seawater infiltration into the water table, permanent loss of groundwater storage capacity, and disturbance to infrastructure like roads and pipelines. Subsidence is also one of the few ways we have to get insight into large-scale groundwater withdrawals (land goes down -> water being taken out and not replaced). Here's a summary with a nice motivational picture showing meters of subsidence over multiple years in the California central valley: https://www.watereducation.org/aquapedia/land-subsidence https://www.watereducation.org/aquapedia/land-subsidence