Study region: The upper and middle reaches of the Wei River basin (U&M-WR) in Loess Plateau of China. Study focus: This research applies the modified Patch-generating Land Use Simulation (PLUS) model to simulate urbanization dynamics, particularly the conversion from Agricultural Land (AGRL) to High-density Urban Residential Land (URHD), and the Soil and Water Assessment Tool (SWAT) to investigate multi-dimensional hydrological impacts of urban expansion in river valley regions, focusing on quantifying urbanization-induced runoff depth changes and identifying the geospatial drivers, assessing shifts in streamflow quantiles and extreme streamflow, and examining impacts on streamflow components and generation mechanisms. New hydrological insights for the region: Urbanization increases the watershed's multi-year average runoff depth. The change in runoff depth caused by per-unit URHD increase (RDC_PU) decreases with higher regional topographic relief, average slope, and maximum elevation. Shifting from discrete to intensive urban expansion increases RDC_PU. Urbanization increases daily/monthly streamflow below the 60 %/65 % quantile but decreases them above those thresholds. It also exacerbates extreme events, with maximum urbanization boosting 100-year floods by 46 % and reducing 95 % dry flows by 26 %. Higher surface flow, alongside reduced lateral flow and groundwater flow, shifts runoff generation toward over-infiltration. These findings emphasize geomorphology's role in shaping hydrological responses to urbanization and offer vital insights for water management, flood and drought disaster mitigation, and urban land use planning in global river valley regions.