Restoration success of the Santa Cruz river heritage project: a remote sensing analysis of recycled urban water impacts, Tucson, Arizona

Abstract

Arid rivers around the world are undergoing rapid hydrological and ecological change due to urbanization, groundwater depletion, and climate pressures. In response to these pressures, the Santa Cruz River Heritage Project (SCRHP) in Tucson, Arizona, reintroduced recycled urban water to restore base streamflow and promote ecological recovery. My study evaluated whether measurable ecological change, specifically in land cover and vegetation, occurred between 2018 and 2023 along the downstream reach influenced by the SCRHP. Using remote sensing tools in QGIS, National Land Cover Database (NLCD) data, confusion matrices, and high-resolution National Agricultural Imagery Program (NAIP) imagery, I compared changes in land cover classification over time for areas around the impacted downstream reach and an upstream control reach of the Santa Cruz River. Losses in vegetation and wetland areas were suggested by NLCD data alone, but high-resolution imagery and error analysis indicated that some of these changes reflected misclassification rather than true ecological change. Although NLCD data detect broad trends, they underestimate fine-scale changes along narrow riparian areas that are critical to evaluate restoration success. These findings highlight the importance of pairing coarse and high-resolution datasets, field validation, and long-term monitoring to more accurately assess restoration outcomes in dynamic arid river systems.