ASSESSMENT OF ROOF CATCHMENT CHARACTERISTICS, RAINWATER QUALITY AND RAINWATER HARVESTING POTENTIAL IN HO CHI MINH CITY

Abstract

Rainwater harvesting and reuse (RWH) is increasingly considered a green infrastructure option to supplement non-potable water supply, reduce roof runoff and support urban flood adaptation. This study assesses roof catchment characteristics and roof-drainage conditions in Ho Chi Minh city based on a household/building survey of 270 sites across five urban zones, combined with remote-sensing–based roof area estimation and event-based monitoring of roof runoff quality (100 samples). Results indicate that metal-sheet roofs dominate (81.9% of surveyed roofs); 74.8% of buildings have functional gutters, while 19.6% lack gutters. The theoretical harvestable volume is about 216.5 million m³/year, with residential land accounting for 86.8%. First-flush runoff exhibits substantially higher TDS and EC than the stable phase (by 54 - 81%), highlighting the need for first-flush diversion and coarse filtration. Increasing trends in heavy-rain days (R30 mm) at multiple stations (1.5 - 2.8 days/decade) suggest that storage sizing and seasonal operation should be updated. Based on these findings, an RWH framework integrated with distributed detention/retention areas is proposed to mitigate peak runoff and alleviate pressure on the urban drainage system. Roof catchment area was mapped using remote sensing and GIS on the Google Earth Engine platform (Open Buildings V3 building footprints).