This study investigates the potential impacts of regional climate change on hydrological cycles using eight years of observations on snowmelt runoff from a small forested watershed (Kurahone watershed) in Nagano Prefecture, Japan. We compared discharge in winter and spring (January–May) in 1991, 1997, 1998, 2003, 2004, 2006, 2012 and 2013. Early years (1991, 1997, 1998 and 2003) were characterized by concentrated-type hydrographs, with concentrated discharge in the beginning of April due to overlaps in snowmelt and rainfall. Later years (2004, 2006, 2012 and 2013) were characterized by sporadic-type hydrographs, with several discharge peaks in midwinter due to rainfall and relatively low ratios of discharge in April to discharge during January to May. Tank-model calculations of discharge rate and snow water equivalent (SWE) over the last 21 years suggest that sporadic-type hydrographs have occurred more frequently in recent years, whereas average air temperature, precipitation amounts and SWE have no increasing or decreasing trends. Discharge in April increased with high maximum SWE and heavy rainfall in April, but decreased with increase of ratios of rainfall to total precipitation in winter. Regional climate change may drive increased midwinter rainfall and the absence of overlaps in snowmelt and rainfall in recent years.