A GIS-based approach to assessing the capacity of rainwater harvesting for addressing outdoor irrigation

The increased demand for water along with limited water supply and climate change has brought about water access challenges globally. Novel and sustainable water management systems are needed for addressing the imbalance between the increasing water demand and limited water resources. Rainwater as a renewable resource presents great potential to help achieve this goal. This study focuses on an important sustainable water management strategy, rainwater harvesting (RWH), and proposes a Geographic Information System (GIS) based method to assess the capability of RWH to meet outdoor irrigation demand at the city scale. High-resolution LiDAR data and orthophotos are used to delineate RWH catchment areas and identify outdoor vegetated sites. Both active and passive RWH are considered in the rainwater supply estimation. Factors including vegetation height, species, density and microclimate variables are incorporated in the outdoor irrigation demand estimation. The approach is applied to study the capacity of RWH in Tucson, Arizona, a semi-arid water stressed city in the Southwestern United States. Results show that the outdoor irrigation in 32% of the Tucson township sections can be met by RWH for more than 8 months of a wet year. The proposed RWH system deployment can lead to an overall savings of 13.8 million U.S. dollars and provides important insights into urban water management and sustainable water planning.