Sustainability of water use in urban green spaces: a multi-city analysis in developing countries

Urban growth is one of the main drivers of global change, with urban population expected to grow from 56% of the world total (2020) to 70% by 2050, mainly in less developed regions. Over the past two decades, more than 80 major metropolises have faced extreme drought and water shortages, with future projections outlining an increasing risk of water crises. In this context, the sustainable management of urban water resources emerges as a critical challenge.  While studies on water scarcity have traditionally focused on agriculture, given its significant impact, urban systems—despite being resource-intensive—receive comparatively less attention. Moreover, most intra-urban studies are limited to specific case studies, lacking a comprehensive and scalable framework for cross-city comparisons.

This work aims to fill this gap, integrating a socio-economic framework with an engineering one to explore the sustainability of water use in urban green spaces. We perform the analysis on 20 cities with populations exceeding one million, located in developing countries, characterized by socio-economic disparities and different climatic conditions (aridity, temperatures, rainfall). Using the "Degree of Urbanization" approach, we define urban system boundaries to ensure comparability across cities. Within these boundaries, we map urban green spaces, using the Normalized Difference Vegetation Index (NDVI) to assess their extent and condition and quantify their green and blue water demand. We combine these data with those relating to water demand for domestic use and assess their overall impact on urban water scarcity. Our domestic water demand data is derived from a global raster dataset (50 km resolution) for the period 2015–2019. We apply a statistical downscaling technique to achieve a finer 2 km resolution, enabling intra-urban analyses. The downscaling process models the relationship between domestic water demand and city-specific indicators, such as population density, relative wealth indices, and monthly climate parameters.

The ultimate goal is to develop an adaptable model to assess the spatial distribution of water sustainability in urban environments. By integrating socio-economic and environmental factors, this research provides new insights into the role of urban green spaces in shaping water demand and urban water scarcity. In a context where climate change and urbanization are intensifying pressures on water resources, this research contributes to a more informed and equitable management of urban water systems.