In snowy regions, the seasonal runoff pattern is greatly influenced by winter season temperature and precipitation. Our objective is to forecast the change in seasonal and monthly runoff volumes resulting from regional climate change scenarios, especially concerning spring snowmelt runoff. Snowmelt Runoff Model (SRM) was applied to Takiya River (19.45 km²) to simulate daily runoff over the period 2000–2007. Snow accumulation and melt was simulated for each of three elevation zones using air temperature data at high and low elevations to estimate the lapse rate. Key model parameters were determined by analysis of the basin monthly water balance, in addition to model calibration using snowpack snow water equivalent and river discharge. Simulation of the IPCC Scenario A2 (high impact) for Niigata region showed that runoff would be 2–3 times greater in winter (Dec–Feb), and decrease by half in spring (Apr–May). Even with warming restricted to +2.0°C, major changes in monthly runoff volumes occur because of large shifts in the proportions of snow versus rain. In Niigata, and other regions that receive heavy snowfall at temperatures close to 0°C, a small rise in temperature causes large changes in the size of the seasonal snowpack and the seasonal distribution of runoff.