Satellite-based agricultural water consumption assessment in the ungauged and transboundary Helmand Basin between Iran and Afghanistan

Abstract

Hamun Lake, the greatest (>8500 km2) freshwater in the Iran plateau, has almost entirely dried over the last 20 years. The flow of the Hirmand (or Helmand) River, the most important feeding river, has decreased from 4.0 to 1.9 km3 in the border of Iran-Afghanistan. In this river basin, the annual water consumption for irrigation is over 90% of the total consumed water. This study aims to calculate the increase in agricultural water consumption in the last two decades. Due to the lack of in-situ data across Afghanistan (including ∼80% of the studied area), this research utilizes remote-sensing. Using Google Earth Engine, land use maps for the years 2002, 2008, 2013, 2017, and 2021 were developed by a supervised classification scheme. Since 2002, it was found that the cropland area has increased from 2008 to 5475 km2. Most cropland has been developed around the Kajaki dam. Based on the Penman-Monteith-Leuning Evapotranspiration version 2 (PML V2) actual evapotranspiration (AET) data (our model assumes the irrigation efficiency equal to 0.3), the annual consumed water has increased from 2 to over 6 km3 in the last two decades. The presented framework in this study can be recommended for other ungauged basins.