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Intercomparison of grace-based groundwater level change and in-situ measurements over Central Anatolia basins, Turkey

Karasu, İpek Gül
The purpose of this study is to validate the satellite- (GRACE) and hydrological model- (GLDAS) based groundwater storage (GWS) change information using in-situ groundwater level observations and investigate the accuracy of Gravity Recovery and Climate Experiment (GRACE) retrievals over Central Anatolia. In this study, GRACE-derived GWS changes from January 2003 to December 2015 are compared with in-situ groundwater level observations from five basins comprising Central Anatolia Basin. The basin areas range between 7,605 km2 and 233,929 km2 which are relatively small according to the footprint of GRACE. It is expected that as the basin area increases the accuracy of GRACE-based GWS variations increase. Also, GRACE is skillful to monitor the large mass changes. The highest correlation between GRACE-based GWS and in-situ observations are found between 0.48 and 0.66 and widely ascribed to the seasonal component. Although Akarçay Basin has the lowest surface area, it has a correlation value about 0.53 which is higher than the correlation value of Central Anatolia Basin (r ≈ 0.45). Especially, in Konya Closed Basin, where groundwater levels are significantly decreasing, the correlation coefficient becomes 0.44. This implies that Global Land Data Assimilation System (GLDAS) estimates and GRACE signals do not represent the ground conditions precisely. Despite these results, GRACE-derived terrestrial water storage variations agreed well with the droughts occurred over Turkey in between 2007-2009 and 2014.