OASIS, an irrigation diagnosis model, is applied to the Zhanghe Irrigation System in central China to investigate the contribution of smaller local storages (in �melons on the vine� configuration) as compared with the main reservoir. Results show that local storages are more important in normal-to-wet years, while the main reservoir is critical in dry years, which implies a strong policy correction relevant to many parts of the world. Balanced investment in various storage infrastructures with associated management practices is a cost-effective strategy for irrigation development