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

Abstract

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.