Blue-green infrastructure solutions for resilient cities

Urban development in all forms impacts the natural landscape, changing vegetation cover, infiltration rates and hydrological (surface and sub-surface) flows. With increasing urbanization urban areas lose a host of natural infrastructure and ecosystem services as ecosystems are modified, degraded and/ or shrunk. Benefits such as flood control, aquifer replenishment, microclimate control, improved air quality are diminished, increasing the risks faced by urban dwellers.

For the Indian context there has been limited study of the interlinked impacts of urbanization on natural infrastructure. In this new report ‘Urban Blue-Green Conundrum’ by WRI India the authors trace the changes to the built footprint (built-up area) and impacts on blue cover (surface water), green cover changes (vegetation) and the groundwater recharge potential.

For the 10 most populated cities in India they analyse satellite imagery to study the core city (0-20 km) and peripheral city (20-50 km) regions and the changes between 2000 and 2015. In addition, the impact on groundwater recharge is estimated from the conversion of natural spaces with higher recharge potential to concretized surfaces with lower recharge potential. Groundwater recharge potential is estimated using the method described in the report titled “The Impact of Climate Change on Groundwater Availability” (Mvandaba et al. 2019).

The potential is derived from the NDVI (Chen 1996) and slope of the land surface (taken from the digital elevation model [DEM]). The method used in this study is limited to the use of satellite imagery and other open-source remote sensing information. It does not use soil maps with detailed infiltration coefficients or evapotranspiration rates derived from on-ground studies.

The cities studied are Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Jaipur, Kolkata, Mumbai, Pune, and Surat. Satellite imagery enables the actual spatial extents of urban areas vis-à-vis built-up areas, blue cover, and green cover change trend to be studied.

The study uses existing spatial assessment and analysis methods to estimate the spatial extents of various built and natural features in 10 Indian cities. It examines changes in extent beyond administrative boundaries, as urbanization processes are not bounded by these jurisdictions. The study considers a 50 km region around each study city to estimate the …


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