Determination of Groundwater Storage Variation, Deficit and Abstraction using GRACE Data in Afghanistan and the Evolution of Vadose Zone in Kabul City using Sentinel-1 Data

Abstract

Groundwater is the main water supply resource in Afghanistan. The country is facing a mismanagement surface water system. To make the groundwater crisis visible, the monthly groundwater storage variation (△GWS) has been calculated in (mm) with a trend value in (mm/month) in the time interval April 2002 to October 2021 by using the GRACE dataset for five major river basins of Afghanistan. The seasonal groundwater storage anomaly reveals a comparatively high negative trend in the Amu-Darya basin (-0.56 mm/month) and a low trend for the Northern basin (-0.13 mm/month). For Helmand, Hari Rud, and Kabul basins the trends are -0.50 mm/month, -0.42 mm/month, and -0.26 mm/month, respectively. The Standardized Precipitation Index (SPI) from the CHIRPS dataset is compared with seasonal △GWS over the five river basins. The comparison revealed a maximum negative SPI value (-1 to -2) in 2004, 2008, 2018, and 2021 indicating extremely to severe drought all over the basins, however, a normal to wet period was experienced from 2013 to 2017. A maximum and a minimum deseasonalized △GWS occurred for Amu-Darya (246 mm to -253 mm) and Hari Rud (89 mm to -102 mm), respectively. The long-term △GWS trend in flux (mm/year) and trend in mass (km3/year) has been calculated for all basins; Kabul (-2.464 mm/year & -0.172 km3/year), Amu-Darya (-4.799 mm/year & -0.426 km3/year), Northern (-0.682 mm/year & 0.053 km3/year), Hari Rud (-4.347 mm/year & -0.432 km3/year) and Helmand (-5.422 mm/year & -1.583 km3/year). The Groundwater Storage Deficit (GWSD) and GWSD Index (GWSDI) calculated, and a negative GWSDI value signified the groundwater drought. The highest negative GWSDI is determined for Kabul and Amu-Darya basins after 2018, whereas the rest of the basins is experiencing drought from 2011 to 2021 consistently. The Groundwater Storage Abstraction (GWSabs) has been analyzed for the whole of Afghanistan region. The estimated GWSabs trend in flux (2003-2021) geving a maximum value of 12.60 mm/year in the Northeast and Southwest parts of the country. The GWSabs trend in mass (2003-2021) calculated from the trend in flux with a maximum value (0.008 km3/year). A Spatio-temporal analysis was done which showed the maximum GWSabs variation up to 20.28 mm during 2005 and again in 2021. The land deformation in Kabul City (2015-2020) has been determined using Sentinel-1 data, and the time-series analysis shows two-phase of deformation. In phase I (2015-2017) there is a low negative trend (-20.66 mm/year in UKBL and -18.54 mm/year in LKBL), but in Phase II (2018-2020) there is showing a high negative trend (-151.34 mm/year in UKBL and -145.32 mm/year in LKBL). The maximum deformation of -395 mm showed up in 2020 for the Upper Kabul.