Rapid subsidence in the Kathmandu Valley recorded using Sentinel-1 InSAR

Urban subsidence poses significant challenges for rapidly developing cities. Published InSAR data reveal Kathmandu as a prime example, demonstrating an alarming rate of subsidence during rapid urban expansion. To monitor the spatiotemporal evolution of recent subsidence, we use Sentinel-1 Synthetic Aperture Radar (SAR) data and the LiCSBAS open-source processing package. Vertical surface motion maps from 2015 to present reveal many localized zones with high subsidence rates (>100 mm year−1), while the mountains that surround the valley have experienced slight surface uplift of ~5 mm year−1. The highest subsidence rate is ~200 mm year−1 and occurs in the centre of the Kathmandu metropolitan area. The distribution of subsidence in the valley matches with areas of the Pliocene to recent sediment up to 500 m thick. The deep aquifer compaction is likely to be the main driver of subsidence in the Kathmandu Valley. Time-series data show a dominant linear subsidence signal with weak sinusoidal signal peaks associated with groundwater recharge of shallow aquifers during the monsoon season. Subsidence rates decrease in proximity to the main river channels, likely driven by the seasonal recharge into the distal floodplain. The distribution of subsidence in the Kathmandu Valley has significant implications for future flood risk and infrastructure in the city.