Quantifying seasonal ground deformation in Taiyuan basin, China, by Sentinel-1 InSAR time series analysis

The presence of seasonal surface deformation in areas that are subsiding/uplifting due to groundwater pumping/ recovery can indicate aquifer recharge. Understanding seasonal surface deformation and the existing relationship between triggering factors and the deformation supports effective groundwater management and subsidence mitigation. Here, we investigated seasonal ground displacement in response to the aquifer compaction and expansion due to groundwater extraction and recharge within the Taiyuan basin, Northern China. We obtained Sentinel-1 InSAR displacement time series data from 2017 to 2020 and quantitatively analyzed relationships between triggering factors (e.g., groundwater level and precipitation) and the associated displacements using wavelet-based methods. The results show that the seasonal deformation is concentrated in the irrigated areas within the central basin, with a 1-year periodicity. The annual peak-to-peak amplitude was up to 2 cm, peaking in March with troughs in August. This seasonality present in the displacement time series is found to be 'in-phase' with respect to groundwater levels and 'anti-phase' in relation to natural precipitation. These results are consistent with the irrigation pumping practices in the basin, with increased groundwater withdrawals to meet irrigation water demand prior to the monsoon precipitation season, resulting in water level decline and land subsidence from mid-March to mid-August. During the non-irrigated season, groundwater extraction decreases, and the aquifer systems are replenished by precipitation, causing water levels to recover and the ground to uplift from late August to mid-March. A geological analysis indicates that the seasonal deformation is controlled by the thickness of Quaternary strata and fault systems, which play a critical role in forming the earth fissures in the basin. The elastic and inelastic deformation was separated; the estimated elastic/inelastic ratio was about 0.6-0.7, indicating that the inelastic component dominates the main aquifer compaction in the central basin. Our analysis is of hydrologic importance which could be used to guide groundwater management and subsidence mitigation, given the inter-basin water diversion projects in this arid basin.