Spatiotemporal evolution model and driving mechanisms of groundwater hydrochemistry in the people’s victory canal irrigation area, 1987–2022

Under the combined influence of climate change and human activities, groundwater hydrochemical evolution has become increasingly complex. Traditional patterns of groundwater hydrochemical evolution have shifted significantly and now show a trend toward diversification. This study analyzes groundwater hydrochemical data (1987–2022) from the People’s Victory Canal Irrigation Area in the middle and lower reaches of the Yellow River. Methods including GIS-based spatial analysis, isotope techniques, UMAP dimensionality reduction, and HDBSCAN clustering were employed to explore the impacts of precipitation, Yellow River diversion irrigation, groundwater flow, and industrial-agricultural pollution on hydrochemical evolution. Results indicate that hydrochemical evolution exhibits distinct regional and phasic characteristics. In the Northwest Zone, high ion concentrations are controlled by geomorphology; the early stage was characterized by evaporation-concentration, while the later stage was driven by the mixing of different types of recharge waters. In other zones, Yellow River diversion irrigation dominated groundwater hydrochemistry during the earlier period; however, as diversion volumes declined, its influence remained significant only near the Canal Head Zone. In the Central Zone, strong runoff caused large fluctuations in ion concentrations, whereas the Northeast Zone, characterized by weak runoff, maintained relatively stable concentrations. Based on a comprehensive analysis of hydrochemical characteristics, internal evolutionary processes, and external drivers, the groundwater evolution is categorized into four patterns: the Palaeo-Yellow River Backswamp–Evaporation Concentration–Mixing Model, the Palaeo-Yellow River Floodplain–Yellow River Irrigation Recharge Model, the Palaeo-Yellow River Floodplain–Yellow River Irrigation Recharge–Runoff Model, and the Palaeo-Yellow River Floodplain–Yellow River Irrigation Recharge–Weak Runoff Model.