Performance assessment of surface-water distribution systems in irrigation networks, particularly under water shortage and reduced water-supply reliability, requires a framework capable of jointly analyzing performance variations across spatial, scenario-based, and multi-indicator dimensions. However, in many operational assessments, the integration of performance indicators and the identification of critical irrigation units are often carried out with limited attention to spatial heterogeneity and changes in water-shortage severity. This study aims to develop and apply a spatial and scenario-based multi-criteria assessment framework for integrating operational performance indicators in the Jarghuyeh–Mahyar irrigation network. For this purpose, the performance of 675 independent irrigation units was evaluated based on adequacy, dependability, and efficiency indicators under eight operational scenarios, including normal conditions and seven water-shortage levels. After directional harmonization and normalization of the indicators, their weights were calculated using the objective Entropy and Principal Component Analysis methods, and an Integrated Performance Index was determined for each unit and scenario. The results showed that the Entropy method was more sensitive to increasing water shortage; the weight of the adequacy indicator increased from 0.44 under the normal scenario to 0.95 under the unprecedented water-shortage scenario, whereas the PCA weights showed more limited variations. The mean IPI decreased from 62.83 to 8.64 under the Entropy method, while it changed from 61.13 to 54.52 under PCA. Spatial zoning also indicated that, under severe scenarios, the Entropy method represented the expansion of the critical class more explicitly, whereas PCA reflected this expansion in a more moderated manner.