Rainwater harvesting potential and impact on stormwater drainage in an urban environment

Climate change is increasingly affecting society, with a strong impact on both water supply and urban drainage. One of the most visible effects is that of increased variability; consequently, more than before, precipitation amounts can now, in any year, be much less, or much higher than long-term average; causing both more frequent water shortages and more frequent flooding events. As this may severely affect urban communities, urban (water) infrastructure resilience needs to increase. One of the ways to achieve this is by adopting rainwater harvesting (RWH) and use. The effects of the gradual adoption of RWH in the city of Campo Grande-MS, Brazil, were studied, using data on population and residences, and historical precipitation data, complemented with long-term measurements of RWH and use for non-potable purposes in three cistern-equipped households. GIS and AI were used for quantification of harvesting surfaces (rooftops) and permeable surfaces from high-resolution satellite images, to calculate expected effects. RWH was shown to have great potential to reduce both demand for drinking water and stormwater runoff volumes. Additionally, discharge of stored precipitation into surface waters, as treated sewage, will occur with significant delay when compared to a situation without rainwater use, which helps counter the increasing variability of river flows.