THE Permanent Court of Arbitration’s supplemental award on Islamabad’s decade-old petition challenging the design specifications of two Indian hydropower projects on rivers allocated to Pakistan under the Indus Waters Treaty is a definitive affirmation of the supremacy of international law over unilateral state actions.

It places India in an increasingly untenable position — legally, diplomatically, and perhaps important, morally. The ruling removes whatever ambiguity India has been trying to exploit. By reaffirming that the IWT remains binding on both parties and that neither can unilaterally suspend it, the decision closes the door on India’s irrational position that it can arbitrarily hold the treaty “in abeyance”.

More significantly, the tribunal has constrained India’s........

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