## 4 Results
### Comparison with Water Surface Area of Eber Lake  
Study [37] claims that the surface area of Lake Eber grew by 2.30% between 1990-2016. However, it has recently been reported by several newspapers that the lake has almost dried up as of October 2018 [47; 48]. Understanding groundwater-surface water relation is a difficult problem and has received much attention in the literature. Several recent studies are focused on this issue. Researchers of [49] studied interactions between lakes/reservoirs/wetlands with groundwater while [50] presented a comprehensive survey of groundwater and surface-water relation, [51] reported the detailed case study about the correlation between groundwater and the surface-water level of Lake Nasser. Nevertheless, it is claimed by [52] that Eber Lake does not directly interact with groundwater and groundwater level changes do not affect the water level. The lake is thought by [35] to be mainly fed by rainfall and spring water coming from the Akarcay and Sultan Mountains. However, it is suggested by [50] that precipitation is also one of the main sources of groundwater level. Thus, both Eber Lake water surface and groundwater level are affected by climate and precipitation. The water surface area of Eber Lake varies over the years due to different amounts of precipitation, evaporation, irrigation, pumping and surface flow [35; 36; 37]. All meteorological information in Turkey, including rainfall data, is collected by The Turkish State Meteorological Service (TSMS). The monthly average precipitation data for the province of Afyon, which was calculated using the data obtained in period 1929-2018, was published on the TSMS website [53]. On the other hand, the Lake of Eber is one of the 5000 lakes on the Earth which is constantly monitored by the Bluedot Observatory. The water surface area of the lake is analyzed using multispectral Sentinel-2 optical data between July 2015 and November 2018 [54]. The percentage of water surface area relative to normal lake boundaries is  
Figure 7: Relationship between geological units in the Bolvadin region and (**a**) Vertical deformation velocity, (**b**) Horizontal (E-W) deformation velocity. The mean (red dots), standard deviation (blue line), minimum and maximum (bold gray) values of deformation velocity are shown for each geological unit. calculated for each Sentinel-2 data. The monthly average rainfall data (mm) and monthly average water surface area (%) of Eber Lake are shown together in Figure 8a. There is quite a good correlation between monthly rainfall data and water surface area of the lake, which shows that precipitation is one of the main sources of Eber Lake. Both rainfall data and water surface area reach to a maximum value in spring and decreases to the minimum level at the end of summer period. Precipitation is one of the main reasons affecting the water surface area of Eber Lake, but another possible reason might be irrigation. One of the water sources of agricultural areas is definitely Eber Lake and surrounding rivers that directly feed Eber Lake. Therefore, extensive use of water in agriculture during the summer period is another important factor in reducing the water surface area to a minimum level. InSAR LOS displacement time series measurements of the point P1 for both datasets are compared with water surface area of Lake Eber obtained from Bluedot Observatory in Figure 8b,c. The long-term linear subsidence trend is subtracted from the LOS time series and then a polynomial (15 th order) model is fit to each time series. There are deficiencies in surface water surface area data, especially in winter seasons due to lack of cloudless optical data. Therefore, missing parts are filled again with a polynomial approximation. It can be observed that the water surface area of the lake falls to its lowest level at the end of the summer period and reaches its highest level in spring. When the water level is minimal, the surface area of the lake falls below 10% of the natural lake boundaries and even close to zero in 2016.