Impact of artificial precipitation on stream water quality during snowmelt season

This study evaluates the impact of wintertime ground-based cloud seeding on stream water quality using data from the Odaecheon-1 site, located downstream of the Cloud Physics Observation Site (CPOS) in Daegwallyeong, South Korea. Since 2006, CPOS has conducted winter cloud-seeding experiments using silver iodide (AgI) and calcium chloride (CaCl 2 ). March water quality data from the baseline period (1997–2005, before the onset of cloud-seeding operations) and the seeding period (2006–2024, after the onset) were analyzed. Time-series analysis revealed increases in water temperature, electrical conductivity (EC), and nitrate nitrogen (NO₃⁻-N), along with decreasing trends in dissolved oxygen (DO) and biochemical oxygen demand (BOD). Seeding-period data also showed greater variability in EC and slightly declining ammonium nitrogen (NH₄⁺-N), suggesting shifts in nitrogen transformation pathways. Correlation analysis revealed a reorganization of inter-variable relationships after seeding began: classical eutrophication linkages such as water temperature–BOD and BOD–Total Phosphorus weakened or reversed, while associations between EC and nitrogen species (EC–Total Nitrogen, EC–NO₃⁻-N) strengthened. The findings suggest that winter cloud seeding may affect not only individual water quality parameters but also the structural relationships among them, potentially altering ecosystem response mechanisms. These results highlight the need for long-term, structure-based monitoring to assess indirect impacts of weather modification technologies.