This study assessed climate change impacts on hydrological regimes in the Budhi Gandaki River Basin (BRB) in central Nepal, covering 3881.16 km2 with an altitudinal range of 315-8163 masl. The Glacio-Hydrological Degree-Day Model (GDM) was employed using historical data (2000- 2023) and CMIP6 projections under SSP2-4.5 and SSP5-8.5 scenarios (2024-2100). Analysis of historical data revealed that BRB receives approximately 1530 mm annual precipitation, with 74% occurring during monsoon (June-September). Temperature data from Dhunibesi station showed a warming trend, with July and August being the hottest months (26°C) and January the coolest (13°C). Discharge at Arughat station exhibited an increasing trend, particularly after 2016. CMIP6 projections indicate little to no precipitation increase in the near-future (2024-2049), with gradual increases in mid- and far-future periods. Temperature projections show a gradual increase under SSP2-4.5 and an alarming rise under SSP5-8.5, reaching around 17°C annually by 2075-2100. The study utilized reclassified LULC maps from 2000 and 2024, incorporating eight classes including debris-covered glaciers. These maps were crucial for calibrating the GDM and simulating future discharge. GDM simulations project decreasing discharge trends compared to the baseline (157.60 m3/s), with reductions of approximately 25% under SSP2-4.5 and 20% under SSP5-8.5 for 2024-2100. Water balance analysis reveals baseflow as the largest contributor (~51%), followed by rainfall (~34%), snowmelt (~10%), and ice melt (~4%). Seasonal analysis shows increased discharge in winter, pre-monsoon, and post-monsoon seasons, but decreased monsoon discharge compared to baseline. The study highlights high spatiotemporal variability in climate change impacts and underscores the need for incorporating glaciers into large-scale hydrological models for improved climate change assessments. This research provides valuable insights for water resource management and adaptation strategies in glacierized Himalayan River basins under changing climatic conditions.