Is Rainfall Collection Efficiency Higher in Urban vs Rural Areas?

Impervious Surface Ratios and Rainfall Collection

Rural areas tend to have lower impervious surface ratios, which means more of the rainfall is absorbed by the ground rather than being diverted into storm drains and sewage systems. For example, a study in the United States found that urban areas have an average impervious surface ratio of 20-30%, whereas rural areas have an average ratio of 5-10%. This significant difference in impervious surface ratios directly impacts the efficiency of rainfall collection systems.

Cistern Sizing and Urban vs Rural Considerations

When sizing a cistern for rainfall collection, urban and rural areas require different considerations. In urban areas, the cistern should be sized to account for the higher rainfall runoff rates, which can vary significantly depending on the size of the catchment area. A good rule of thumb is to use the 1:10 to 1:5 rainfall runoff ratio for urban areas, whereas rural areas can typically use the 1:5 to 1:2 ratio. This difference in rainfall runoff ratios is crucial for accurate cistern sizing to avoid overflow and ensure efficient water collection.