Assessment of Groundwater Level Variations in Different Land-Uses Using GRACE Satellite Data (Case Study: Zayanderud Basin, Iran)

Reduced rainfall, groundwater resource limitations, and undesirable use of it are the main limiting factors of the development of different uses in arid and semi-arid areas. Changes in surface factors have an effective role in groundwater level because some factors such as vegetation and land use cause changes in groundwater balance. In this study, data from the GRACE satellite and the stations were used to estimate the monthly groundwater level changes in the Zayanderud Basin, Iran from 2002 to 2018. In addition, the annual and seasonal storage of groundwater in this basin was estimated and verified using the GRACE data and this trend was compared with the data from previous rainfall. Our results indicate that terrestrial water storage variations from GRACE and GLDAS are in general consistent with one another. These data show that the current groundwater level depends on the amount of rainfall in the past years. When rainfall is on a downtrend, underground water storage fluctuations are more effective than rainfall. In addition to time trend, vegetation pattern in rangelands, woodlands, and agricultural lands depends on the amount of groundwater storage variations in the Zayanderud basin. The lowest amount of that in 2016 coincided with the lowest amount of underground water storage and recharge (27.36 cm). The statistical correlation analysis of the GRACE satellite data and the observed data of wells indicated that RMSE was equal to 2.23 cm on the seasonal scale. Further, GRACE captures characteristics of groundwater drought that occur as a result of complex human activities and natural changes, thus presenting a framework to assess groundwater drought characteristics.