The international legal principle of ‘no-harm’, as a customary international law, lies at the heart of numerous international transboundary water conventions, rules, and agreements. The current study identifies and examines the three most common categories of harm, namely health, environmental, and economic, in an integrated framework. Exploitation of the Kamal Khan dam over the Hirmand/Helmand Transboundary River internationally shared between Iran and Afghanistan has been selected as a case study. For this aim, an integrated modeling approach that links Soil and Water Assessment Tool (SWAT), Indicators of Hydrologic Alteration (IHA), dust storm events (DST) and crop production is developed to simulate the indicators and their parameters under historical conditions and future exploitation of the dam. Effects on the three types of harm are classified as being low, moderate or high. The results showed that the effects of the dam diversion for economic harm would be high. For instance, it could reduce the wheat production of the Iranian side of Sistan plain up to 70%. The hydrological alteration of the river is also significant, up to 80% during the winter and spring months. This can result in health and environmental harms. The region’s health and environment are already in a critical situation mainly due to the drying of Hamoun wetlands, which rely on the inflows of the Helmand River and are the major sources of dust storms. Notably, these issues would affect the entire plain in both Iran and Afghanistan. The scope of this study was the principle of ‘no-harm’ but the methodology with some additional modifications could be considered for other principles like “equitable and reasonable utilization” in transboundary river basins.
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