Informal green space contribution to city’s recreational green open space need of a densely populated old city: A case of Patna, India

India’s population increase has affected the Urban Green open space (UGOS). This population explosion has resulted in insufficient outdoor recreational spaces in many cities, especially in the old cities with higher population densities. The study focuses on identifying the potential recreational open spaces or Informal Green Open Spaces (IGOS) and analyzing their contribution to the city’s recreational needs in Patna city. The study used the quantitative comparison of urban green open spaces with and without informal or potential urban green open spaces at ward and city levels. Also, the prediction model, Geographically Weighted Regression (GWR), using the Arc Map tool, is used to compare the observed value of total urban green open spaces and the predicted value of formal urban green open spaces. The analysis is done based on quantity and accessibility as parameters. The result shows improvement in cities per capita and serving population of open space within the city. With the inclusion of Informal Green open spaces, a 3.1 m² per capita URDPFI standard for recreational open spaces at the community and district level is achieved for the 2030 population. Also, the catchment area as per 400m range from open space has increased to 82%, and the serving population of open space has increased to 87%, from 63.7% and 69%, respectively. The IGOS has an overall contribution of 29% in the total UGOS, including IGOS. The contribution of IGOS to the Total Open space of the city is significant and helps in filling the lacuna and achieving the quantitative standard of the open space in the city. And helps in contributing to the SDG goal 11 and helps in contributing to the smart city initiative.