Remote sensing insights into water allocation and evaporation challenges in the Hirmand River Basin, after the operation of Kamal Khan Dam

The Hirmand River Basin is a vital transboundary river system, that originates in Afghanistan’s Hindu Kush Mountains and flows into the Sistan Depression, and encompassing the Chah Nimeh Reservoirs in Iran and the Godzareh Depression in Afghanistan. The Kamal Khan Dam, constructed on the Hirmand River in Afghanistan, has significantly altered the downstream water direction and distribution between the Chah Nimeh Reservoirs and Godzareh Depression. Utilizing remote sensing techniques, particularly Landsat 8 satellite imagery and the FAO 56 PM as a evaporation retrieval method, the research focuses on evaluating changes in water allocation and evaporation rates in these regions over the past decade. The findings reveal that after operation of the Kamal Khan Dam, water allocation to the Chah Nimeh Reservoirs has drastically decreased, leading to a 54 % reduction in their average area from 2020–2023 compared to the previous years. Conversely, the Godzareh Depression, now receiving the redirected water, has experienced significantly higher evaporation rates, contributing to substantial water losses. These changes underscore the critical need for effective water management strategies to address the escalating water scarcity and hydrological imbalances in this arid region. • Remote sensing study of transboundary water. • Kamal Khan Dam reshapes Helmand River flows. • Water shifts worsen Iran- Afghanistan water stress. • Higher evaporation in Godzareh depression compared to Chah Nimeh. • The entire basin experiences increased evaporation and more water lost post-dam.