Urban stormwater planning increasingly adopts Low Impact Development (LID) to reduce runoff and pollutant loads, yet most evaluations rely on average performance metrics and overlook system sensitivity and vulnerability under changing water-quality pressure. This study develops a risk-informed environmental sustainability indicator to support resilience-oriented prioritization of urban LID systems by integrating event-scale hydrologic-water quality simulation with decision-relevant criticality metrics. Runoff and total suspended solids (TSS) were simulated using the Storm Water Management Model (SWMM) under baseline and alternative LID scenarios in a densely urbanized, semi-arid district of Tehran. Model outputs were transformed into normalized performance indicators and complemented by representative absolute reductions to preserve physical interpretability. System influence was quantified through removal-based sensitivity analysis, while degradation likelihoods were incorporated to derive failure-aware risk metrics. Ranking robustness was evaluated across low, medium, and high TSS scenarios, and results were integrated into an Extended Criticality Index (ECI) combining cost, performance, sensitivity dominance, and risk exposure. The ECI functions as a composite sustainability indicator capturing functional dominance, degradation vulnerability, and pollution response to inform resilient urban drainage decision-making. Results show that bioretention exhibits the highest criticality due to dominant system influence and stable performance across pollution scenarios, whereas permeable pavement demonstrates lower criticality because of limited sensitivity contribution and greater susceptibility to clogging-related degradation. Overall, the framework highlights the value of indicator-based criticality assessment for sustainable stormwater planning under environmental uncertainty.