Background: The Qazvin Plain is one of Iran’s largest and most important agricultural regions. It is situated on the Qazvin aquifer. Understanding the relationship between surface features such as topography, land use, and soil type with the quantitative and qualitative characteristics of the aquifer is crucial for this region. Methods: In this study, the Soil and Water Assessment Tool (SWAT) model was used to delineate the hydrological response units (HRUs) of the plain. These units were calculated based on common characteristics, including land use, topography, and soil type. Additionally, the MODFLOW model was used to simulate groundwater levels based on the hydraulic conductivity (K) map, well pumping tests, and other parameters. This model served as a quantitative indicator of groundwater resources. Furthermore, the spatial distribution map of electrical conductivity (EC) values was used as a qualitative indicator of groundwater resources. In the Qazvin aquifer, EC is the most important limiting factor for water quality. The relationship between these factors was then analyzed using geographically weighted regression (GWR). Results: The values of EC with a statistic of R2 = 0.66 and groundwater level with a statistic of R² = 0.79 were controlled by surface characteristics, indicating a strong relationship between these variables and surface features. Conclusion: This research can highly assist water and environmental resource managers and decision-makers in managing the quantity and quality of water in this region.
