Assessment of land use and climate change effects on land subsidence using a hydrological model and radar technique

The impact of land use and climate change (LUCC) on the pattern of groundwater and land subsidence at the Marand Plain was investigated in this study. Earth deformation was derived from ENVISAT ASAR (2003.12.17-2006.03.01) and Sentinel-1 (2015.05.03-2015.10.18) satellite data via the Synthetic Aperture Radar Interferometry (InSAR) small baseline subset (SBAS) time series analysis method. Time series analysis results showed the maximum deformation rate of 24 and 39 cm/yr extracted from ENVISAT ASAR and Sentinel-1, respectively. About 3141 ha of the plain area have been affected by the subsidence phenomenon, which has caused severe damage to constructions. Observed groundwater level (GWL) observed data, indicate a reduction of five meters on average for the period of 1997-2015. Linear regression was derived between GWL abatement and subsidence with average correlation coefficient of 0.73 and the rate of subsidence was about 2.6-8 cm for a one meter drop in the GWL. Owing to the obtained relations between GWL reduction and subsidence, the effects of LUCC on groundwater storage (GWS) variability, and consequently the plain subsidence was studied using the Soil and Water Assessment Tool (SWAT). Climate change scenarios were represented by the delta change approach based on the trend for the past three (1985-2014) and last decade (2005-2014), respectively by low delta change (LDC) and high delta change (HDC), where the trend of the most recent decade yield a higher delta change when extrapolating into 2030. After calibration and validation of the SWAT model using the monthly flow data, baseline (Sb) and five different LUCC scenarios (S1-S5) were simulated and their effects on the GWS variability were compared with together. The simulated results of Sb vs. S4 and S5, which represent plausible scenarios show that LUCC may decrease GWS about 52-99% and 85-100% under LDC and HDC, respectively. The results of the scenarios show the significant value of climate change (CC), under HDC, compared to land use change (LUC) in the diminishing of the GWS and as a result, the severe occurrence of the subsidence in the region.