Imaging land surface subsidence hazard across Iran using Earth Observation data

Groundwater constitutes 99% of Earth’s liquid freshwater, providing half the volume of water withdrawn for domestic use. In Iran, groundwater provides 90% of the country’s agricultural sector water needs. However, modernisation of Iran’s groundwater management approaches has resulted in groundwater overdrafts and salinisation. One consequence of groundwater depletion is land surface subsidence, the lowering of the land surface over time due to sediment consolidation.

Spaceborne monitoring is the most common technique for monitoring land subsidence. In this thesis, I use Sentinel-1 InSAR to identify 106 land subsidence regions totalling 31,400 km2 across Iran. I generate vertical and East-West surface velocity fields for these regions at ~100 m resolution using ascending and descending velocities and GNSS. I demonstrate the application of surface velocity gradients in providing evidence for geological controls on subsidence patterns for seven Iranian cities. I use Independent Component Analysis to isolate an inelastic component of subsidence for all 106 regions, demonstrating all subsiding regions in Iran are permanently losing aquifer groundwater storage capacity.

I difference satellite LiDAR returns and Digital Elevation Models to retrieve land subsidence magnitudes in south-west Tehran, 2012-2024. South-west Tehran is a noise rich environment for testing topographic differencing potential, including dense urban areas, agriculture, and quarries. Calculated land subsidence magnitudes are within +/-20-30 cm of those estimated using InSAR, an error magnitude similar to that reported in previous work investigating satellite altimetry accuracy.

Finally, I investigate UK researchers’ perceptions of researching geohazards using satellite data, and the ethics related to communicating and sharing this research. I compare these perceptions to guidelines and expectations of these researchers which are established in the Sendai Framework for Disaster Risk Reduction 2015 and Geoethics principles. My findings have the potential to inform future ethics education, outreach, and guidelines in relation to researching geohazard using satellite data.