Assessing the feasibility of an irrigation daminvestment and optimizing expected returnsrequire detailed ex-ante appraisal.• Due to the inherently complex and uncertainconsequences of irrigation dam investmentsand often severe data scarcity, traditional costbenefitassessment methods face limitations.• Stochastic Impact Evaluation (SIE; Luedelingand Shepherd 2016) attempts to overcome theparticular challenges of evaluating investmentsin such contexts.