Navigating Urban Floods: Spatio-temporal Analysis of Blue-Green Infrastructure and Urban Densification in Indian Cities

Cities face risks and pressures to meet infrastructure needs, often at the cost of natural resources. Blue-Green Infrastructure (BGI), like lakes and green spaces, serves as cities' "innate" immunity, mitigating risks like urban flooding. BGI’s flood-mitigating functions transcend administrative boundaries, requiring a catchment-based approach. Furthermore, due to India’s varied geography, the endogenous (local) and exogenous (regional or external) factors have different influences on the intensity of urban flooding in different city regions. However, current plans and policies, limited by administrative divisions, fragment BGI and weaken its flood mitigation capacity. Therefore, informed decision-making by urban policymakers is crucial for building future-proof cities.

Approach and Study Area: This study views cities as interactive layers, examining built-up intensity, city-level BGI transformations, and urban flooding hotspots. It highlights the interplay between urban densification, urban flooding hotspots, and BGI functioning in the catchment i.e. city-region. The study areas for this research are two urban agglomerations of India, namely, Pune and Bangalore. They’re among India’s 10 largest urban agglomerations. The findings from the case studies will highlight region-specific challenges and opportunities for integrating BGI into localized urban flood management strategies.

Methods and Data: The study will use a quantifiable approach by measuring the annual changes in values of three spatial indices – Normalized Built-up Index (NDBI), Enhanced Vegetation Index (EVI), and Modified Normalized Difference Water Index (MNDWI). The choice of these spatial indices is based on their ability to capture and differentiate the transformations in the complex urban fabric which are often overlooked in traditional spatial analysis. Open-access satellite data at a medium-spatial resolution i.e. 10- 30 m for the period 2000-2025 will be used for calculating the above indices. Simultaneously, the in-situ data on urban flooding will be overlayed to identify areas under high risk. Thereafter resulting in the mapping of patterns of built-up intensification, BGI configurations, and urban flooding.

Key Findings: The findings provide evidence to comment on the nature of the relationship between urban densification and BGI at the city-region scale; and its association with localized urban flooding. Using GIS-based methods and annual datasets for EVI, MNDWI, and NDBI will uncover spatial and temporal BGI trends, addressing how densification impacts BGI’s effectiveness in mitigating urban flooding. This research's findings will contribute to scientifically informed and tailored urban hazard management strategies.

Novelty and Future Relevance: Geo-information Science has emerged as a vital tool for studying spatial transformations and detailed analysis of India's rapidly evolving urban environments. This research extends the limited temporal analyses of changes in BGI and urban densification in Indian cities. Traditional spatial analyses, like land cover change detection, often miss urban complexities. By integrating annual datasets of the chosen spatial indices for the past two decades and in-situ knowledge of urban flooding, the study reveals unexplored trends in India’s urban growth dynamics.