Insights on urban expansion control around the urban waterbodies of developed and developing countries using remote sensing

Urban lakes are vital ecological assets that support biodiversity, groundwater recharge, and urban flood regulation but face growing threats from rapid urbanization and the expansion of impervious or “grey” surfaces worldwide. This global trend leads to the degradation of blue (water) and green (vegetation) ecosystems, particularly in developing regions where urban growth outpaces planning and regulation. Despite extensive research on blue–green infrastructure, few studies provide comparative, quantitative assessments of long-term blue-green–grey dynamics across contrasting urban contexts. This study addresses that gap by analysing multi-decadal (1990–2024) Landsat imagery to assess land cover transitions around five lakes—three in Charlotte, USA, and two in Gurgaon, India. It develops novel landscape interaction indicators (Green-to-Blue, Blue-to-Green, Green-to-Grey, and Blue-to-Grey ratios) to quantify ecosystem shifts and forecast ecological tipping points. Results show that Charlotte’s lakes maintain relatively stable blue-green–grey ratios due to effective planning and buffer enforcement, with annual grey surface expansion rates of 1.9–5% and projected ecological sustainability beyond 57 years. In contrast, Gurgaon’s lakes experience rapid grey growth (5.8–6% annually), sharp declines in blue and green areas, and critical ecological lifespans of only 26 years for Badshapur Lake and 34 years for Najafgarh Lake. The study introduces the blue-green–grey ratio as a novel metric to assess ecological resilience and guide sustainable urban development. By demonstrating how planned growth sustains lake ecosystems, this research emphasizes the urgent need for nature-based solutions, buffer zoning, and land-use control policies in developing cities to prevent irreversible urban lake degradation.

The study conducts a 34-year spatio-temporal analysis of blue-green-grey surfaces around five lakes in Charlotte (USA) and Gurgaon (India), revealing long-term ecological transitions driven by urbanization.