Resilience is the ability of a system to withstand stressors while preserving its structure and functions. Various performance- and attribute-based resilience assessment frameworks have been developed to understand the behaviour and properties of individual water systems. However, in integrated water systems, the increased complexity presents new challenges in the application of these frameworks. This study first reviews the key elements in both frameworks, including system indicators, thresholds, and resilience metrics, across urban water supply, drainage, groundwater, and river systems. Challenges are identified in deriving consistent indicators from siloed subsystem models, robust threshold selection, and resilience metrics synthesis as well as their usefulness for management. Based on the insights, a bottom-up resilience assessment framework for integrated water systems is developed. A water system integration model (WSIMOD) is employed to derive indicators for subsystems. Four performance-based resilience metrics are designed and applied to the indicators to facilitate intercomparison between subsystems. The application of the metrics crosses from event-level assessments for understanding system behaviour to annual-level evaluations of long-term performance, which are ultimately synthesised at the system level for multi-stakeholder decision-making. The efficacy of this framework is demonstrated through a case study in Luton, UK. The findings highlight river water quality as the least resilient subsystem that needs prioritised management. Sensitivity analysis is conducted to examine the impacts of thresholds on resilience results, with subsequent interpretation linking these metrics to specific decision variables for enhanced management. This framework can be extended through stakeholder engagement to improve system performance under deep uncertainties.

Urban-rural nature-based solutions (NBS) have co-benefits for water availability, water quality, and flood management. Searching for optimal integrated urban-rural NBS planning to maximise these co-benefits is important for catchment scale water management. This study develops an integrated urban-rural NBS planning optimisation framework. In this framework, the CatchWat-SD model is developed to simulate a multi-catchment integrated water cycle in the Norfolk region, UK. Three rural (runoff attenuation features, regenerative farming, floodplain) and two urban (urban green space, constructed wastewater wetlands) NBS interventions are integrated into the model at a range of implementation scales. A many-objective optimization problem with seven water management objectives to account for flow, quality and cost indicators is formulated, and the NSGAII algorithm is adopted to search for optimal NBS portfolios. Results show that rural NBS have more significant impacts across the catchment, which increase with the scale of implementation. Integrated urban-rural NBS planning can improve water availability, water quality, and flood management simultaneously, though trade-offs exist between different objectives. Runoff attenuation features and floodplains provide the greatest benefits for water availability. While regenerative farming is most effective for water quality and flood management, though it decreases water availability by up to 15% because it retains more water in the soil. Phosphorus levls are best reduced by expansion of urban green space to decrease loading on combined sewer systems, though this trades off against water availability, flood, nitrogen and suspended solids. The proposed framework enables spatial prioritisation of NBS, which may ultimately guide multi-stakeholder decision-making.