Ecological Flood Resilience Index (EFRI) to Assess the Urban Pluvial Flood Resilience of Blue-Green infrastructure: A case from a southwestern coastal city of India

Abstract

Urban pluvial flood resilience planning must account for the ecological capacity to absorb, adapt, and transform with floods. Research on flood resilience indices highlights resilience as a normative condition, characterized by the return to equilibrium or the recovery time. However, the socio-ecological approach, including adaptive, absorptive, and transformative capacities is often overlooked, and the determinants of these capacities are underexplored. The present study addresses this gap by proposing an impact-based composite index to measure the flood resilience of urban Blue-Green Infrastructure (BGI). An eight-step procedure was used for the composite index construction. Statistical correlation and regression analysis established indicator appropriateness, and Principal Component Analysis (PCA) was used for weighing and aggregation. The Ecological Flood Resilience Index (EFRI) was developed and applied to the city of Kochi, India to assess the ability of existing urban BGI to temporarily store, infiltrate, and delay runoff, indicating the capacity of the system to withstand urban flooding. The index was validated using crowd-based data followed by sensitivity analysis. The EFRI Map outlines that the highly urbanized low resilient central areas, marked by poor vegetation and disrupted natural drainage contribute to flooding in various parts of the city. A comprehensive analysis of the 37 % regions of the city that falls within ‘very low’ to ‘extremely low’ resilience is essential to understand the critical factors in flood resilient spatial planning. The proposed composite index is significant for its novelty and theoretical clarity in resilience evaluations, promoting a shift from risk-based to resilience approaches in urban flood management.