## 5 Discussion  
Within the scope of this study, land subsidence due to groundwater over-pumping in the Karapinar region was determined by the InSAR time series using 25 COSMO-SkyMed images acquired between 2016-2017 and 87 Sentinel-1A images acquired between 2014-2018. The results reveal that the Karapinar region experienced significant land subsidence, reaching 60 mm/year from 2014 to 2018. A similar study conducted by [35] indicated that land subsidence rates in Karapinar during the years 2002-2010, as determined by Envisat data, was approximately 15 mm/yr. The increasing subsidence rate in recent years, compared to a decade ago, indicates an acceleration in the rate of subsidence, which we attribute to the increasing extraction of groundwater in the area. The main reason for this higher groundwater extraction is the gradual conversion of farming practices from non-irrigated agriculture in the region two decades ago to irrigated agriculture since 2010. This study relies on two datasets, X-band COSMO-SkyMed and C-band Sentinel-1A, which detected similar rates and spatial patterns of subsidence (Figure 4). However, there are three main differences between subsidence maps calculated from the two datasets. First, the subsidence detected by the Sentinel-1A dataset covers a significantly larger area than COSMO-SkyMed, because the swath of the Sentinel-1 scene is 250 km wide, whereas the swath of COSMO-SkyMed is only 40 km. Second, the coverage of the Sentinel-1A dataset within the same frame as COSMO-SkyMed is more continuous, reflecting a better coherence of the C-band Sentinel-1A compared to the X-band COSMO-SkyMed data. The improved coherence of the Sentinel-1 data reflects the use of longer radar wavelength, but also the improved repeat orbits of the Sentinel-1 mission, which are constrained within the 150 m envelope compared to the >1000 m envelope of the COSMO-SkyMed mission (see perpendicular baselines in Figure 3). Third, the COSMO-SkyMed dataset had a slightly higher subsidence velocity value than those produced from Sentinel-1 data. The higher rate of the COSMO-SkyMed data was calculated from an only 19-month period, in which groundwater level drop was very rapid due to the excessive usage (Figure 7). Consequently, the subsidence velocity during the fast-dropping water level period (COSMO-SkyMed) is higher than the mean velocity during the longer period (Sentinel-1), which includes periods of fast and slow rates of water level drop. The temporal subsidence pattern obtained from the GNSS, COSMO-SkyMed, and Sentinel-1 observations revealed a continuous subsidence with a significant seasonal com  
Figure 8: Cross-Correlation histogram between groundwater level and land subsidence derived from GNSS, COSMO-SkyMed, and Sentinel-1. ponent (Figure 7). The amplitude of the seasonal component was in the range of 10-30 mm, which varies from one year to another. The seasonal component was also noticeable in the COSMO-SkyMed interferogram time series showing a lower subsidence rate during the winter and spring months compared to a faster rate during the summer months (Figures 5 and 6). The seasonal subsidence signal follows with a minimal lag in the observed seasonal component of groundwater level (Figure 7), suggesting a time-independent surface deformation response to seasonal water level changes. Similar seasonal subsidence behavior was observed in many locations, including Las Vegas [4; 52], California [53], and Beijing [54]. The seasonal subsidence component reflects poroelastic deformation of the aquifer system in response to stresses induced by seasonal hydraulic head changes [55]. The Karapmar region is subjected to both land subsidence and sinkhole activity. Our InSAR time series analysis revealed that land subsidence occurred non-homogenously in patches of variable sizes ranging from hundreds of meters to several km in width (Figures 4 and 9).