Estimation of groundwater storage change and recharge using grace and gldas data, Firat basin, Turkey case

Groundwater plays an important role in the hydrologic cycle and it is one of sources of drinking water for about half the world's population. Groundwater is one of the main sources of water supply used for irrigation in agriculture and human consumption in Fırat basin. The groundwater water storage in Fırat Basin is mostly influenced by soil moisture, groundwater, snow water equivalent and plant surface water. In this research, the GRACE and GLDAS data sets are used, for 11 year period to estimate Terrestrial water storage and change over the Fırat basin on the Turkish side. Subsequently, the estimates are used to derive groundwater storage and to further estimate the groundwater recharge on the entire basin. The groundwater storage anomaly is obtained by subtracting the sum of the state variables of GLDAS from the Terrestrial water storage anomaly of GRACE. The groundwater recharge is estimated from time series of groundwater storage using water table fluctuation method. According to the estimated groundwater storage, the time series shows decreases in the groundwater at rate of -12.40 mm year-1 in the entire basin. The averaged annual groundwater recharge in 11 year period over the entire Fırat basin was 279.26 mm year-1. The annual recharge varies from 174 to 351 mm/year and 33 % can be explained by the variability in precipitation. And the correlation coefficient of annual recharge and precipitation is 0.33. Understanding the groundwater storage changes and groundwater recharge estimation are important in hydrological fields because this can lead to sustainable use of groundwater resources. Keywords: GRACE, GLDAS, groundwater storage, water table fluctuation, groundwater recharge, Fırat Basin