Densification to deluge: a city-region approach to investigate blue-green infrastructure transformations and urban flooding in the Indian context

Indian cities are becoming highly susceptible to urban flooding due to intensifying climate extremes and accelerated urban expansion. However, flood management strategies are predominantly limited by administrative boundaries, overlooking the ecological systems that transcend these limits. This study applies a city-region approach to analyse the temporal dynamics of urban densification, blue-green infrastructure (BGI), and precipitation, for two Indian metropolitan regions: Pune and Bangalore. A spatio-temporal analysis has been conducted using three spatial indices: the normalized difference built-up index (NDBI), the enhanced vegetation index (EVI), and the modified normalized difference water index (MNDWI). The analysis aimed to identify patterns of built-up change, BGI transformations, rainfall trends and co-occurrence with locations of flooding. The results indicate that the flooding locations in Pune and Bangalore exhibit low NDBI, EVI, and MNDWI values. This suggests that the flooding locations are spatially co-occurring with areas with low BGI and less built-up density areas. The study also presents comparative insights into the spatial distribution across the two city-regions and reflects on the limitations, challenges, and way forward for urban flooding studies in the Indian context.