This study evaluates the impact of projected climate change on the water requirements of summer squash (Cucurbita pepo L.) cultivated under bare and mulched soil conditions in the Kuyavia region (central Poland). The study is based on long-term meteorological observations and climate projections, combined with the FAO Penman–Monteith method and crop coefficient (Kc) approach. Water requirements were estimated based on reference evapotranspiration (ETo) calculated using the FAO Penman–Monteith method for the reference period (1981–2010) and the forecast period (2021–2050). Rainfall deficits were determined using the Ostromęcki method. The results indicate an increase in water requirements during the forecast period for both cultivation systems, amounting to 27.4 mm (8.2%) for bare soil and 23.8 mm (8.7%) for mulched soil over the growing season. The highest increase is expected in August (approximately 16%), identifying this month as the most critical for irrigation. Mulching significantly reduced water requirements by approximately 18–19% compared to bare soil. Rainfall deficits are projected to increase substantially, particularly in July, and may reach up to 310 mm during very dry years for bare soil conditions. The findings highlight the growing importance of irrigation in Central Poland under changing climatic conditions and demonstrate the effectiveness of mulching as a water-saving practice. The results may support irrigation planning and the design of water storage systems for sustainable crop production.