Where the City Meets the Lake: Urban Encroachment into the Catchment of the Upper Lake (Bhoj Wetland), Bhopal

Bhopal's Upper Lake (Bhojtal), the core of the Ramsar-listed Bhoj Wetland, has been the focus of conservation since 1989: buffer planting from that year, a catchment-protection project financed by the Japan Bank for International Cooperation from 1995 to 2004, and Ramsar designation in August 2002, midway through that project. This paper asks two separate questions: whether the lake's water surface has shrunk, and whether building growth on the land around its shore slowed as protection took hold. The lake's catchment (367.4 km²) was traced from the Bhadbhada dam using MERIT Hydro flow directions, and the land around the lake was divided into four shoreline distance bands (0–50 m, 50–300 m, 300 m–1 km and 1–3 km). Building growth in each band was measured from the Global Human Settlement Layer (1975–2020) and checked against Google's Open Buildings temporal data (2016–2023), calibrated against 102,937 building footprints from 50 cm imagery. Identical bands around eleven reservoirs within 40 km that lack comparable protection form the comparison set for a difference-in-differences test before and after 2000, and the lake's water extent was tracked with the JRC Global Surface Water record for 1990–2021. Building growth within 3 km of the Upper Lake slowed after 2000, from 0.197 to 0.127 percentage points a year, while growth around the pooled comparison reservoirs slowed only slightly. The slowdown is concentrated between 50 m and 1 km from the shore and fades by 1–3 km. A placebo test ranks the Upper Lake second of twelve sites; the one reservoir that slowed more, Hathaikheda, had largely run out of room to build. The lake's water surface shows no long-term decline. The pattern fits the sustained physical catchment works more closely than the Ramsar label itself.

Bhoj Wetland, urban growth, difference-in-differences, Global Human Settlement Layer, Ramsar site

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