Ecological drought and its impact assessment on the water yield ecosystem service of the Hamoun triple lakes in Southeast Iran

Ecological drought threatens arid endorheic basins, yet its assessment often relies on indirect indices that fail to capture functional ecosystem collapse. This study proposes a consequence-based framework to directly evaluate ecological drought in the transboundary Hirmand-Hamoun basin. Integrating a 40-year meteorological analysis (SPI, 1985–2024) with land cover change detection and InVEST hydrological modeling, we quantified the collapse of the water yield ecosystem service and established it as a direct metric for drought severity. Results reveal that prolonged droughts triggered a 95% loss of the Hamoun wetlands’ open water area. This landscape degradation caused a catastrophic 85% decline in the basin’s endogenous water yield, which fell from ~77 million cubic meters (MCM) in a wet year (1986) to just ~10.8 MCM during a severe drought (2016). The study’s primary contribution is operationalizing this quantified service collapse as a direct metric of lost ecosystem resilience. This outcome-based approach offers a significant advantage over traditional indices by translating climatic stress into a clear measure of functional failure, providing critical insights for managing fragile transboundary basins.