Estimation of long-term groundwater storage variation in the Lower
Transboundary Indus Basin using GRACE and WGHM model data
Abstract
In the Lower Transboundary Indus Basin (LTIB), excessive groundwater is
being consumed in combination with surface water to meet the increasing
demand of irrigation, resulting in groundwater depletion that needs to
be quantified. This study used GRACE (Gravity Recovery And Climate
Experiment) satellite terrestrial water storage anomalies (TWSA) and
Global Land Data Assimilation System (GLDAS) model data to produce
monthly groundwater storage anomalies (GWSA) and to evaluate the
depletion of groundwater storage in the LTIB. It is observed that the
variation in GWSA exhibits a downward trend from 2003 to 2016.
Additionally, TWSA and precipitation data depict seasonal
characteristics with peaks in the summer and dips in the winter, which
reflect variation in GWSA, respectively. GRACE TWSA measurements also
detected massive floods that occurred in 2010 and 2015, and they
significantly recharged groundwater in the LTIB. This study also
utilized Empirical Orthogonal Function (EOF) analysis to assess the
variance variability. The results revealed that more than 80% of total
variance variability was explained by the first 2 EOF modes. The
generalized three-cornered hat method (GTCH) was used to estimate the
uncertainty of different GRACE TWSA measurements. The results show that
groundwater storage is being depleted at a rate of 4.16 mm per year
(2.97 km3 per year). Long-term monthly mean GRACE derived GWSA showed
remarkable agreements with PCRaster Global Balance (PCR-GLOBWB) model
75% and WGHM (WaterGap Global Hydrological model) 81%. This study can
be helpful to calculate the socio and agro-economic impact of the
excessive withdrawal of groundwater.