Leveraging Sustainable Green Water Resources to Mitigate Urban Heat: A Case Study of the Green Riyadh Program

Urban heat intensification in hyper-arid cities is one of the most urgent environmental challenges of our time. As global temperatures climb and urbanization surges, desert megacities contend with low vegetation, high solar radiation, and vast impervious surfaces—factors that enhance the urban heat island (UHI) effect. This study examines the relationship between sustainable “green water” resources—specifically treated wastewater—and expansive afforestation as a climate mitigation strategy. Through the lens of the Green Riyadh Program, we investigate how a 1,350 km irrigation network delivering 2.7 million m³/day of treated water facilitates the planting of 7.5 million trees and expands green space from 1.7 to 28 m² per capita. The program seeks to reduce overall city temperatures by 1.5–2°C, with localized cooling in intensively vegetated corridors reaching 8–15°C. A methodological framework utilizing satellite-based Land Surface Temperature (LST) and the Normalized Difference Vegetation Index (NDVI) is presented to quantify the thermal impacts of greening. Our findings underscore the transformative potential of circular water systems for sustainable urban cooling and provide policy recommendations for replicating this approach in desert megacities.