The growing energy demand in developing countries necessitates sustainable electricity generation solutions that address both climate mitigation and water security challenges. Floating photovoltaics (FPV) on reservoir surfaces offer a dual-benefit approach by generating clean energy while reducing water evaporation-critical in water-stressed semi-arid regions. This study presents a comprehensive feasibility assessment of large-scale FPV deployment across dam reservoirs in Razavi Khorasan Province, Iran, using an integrated remote sensing, GIS, and multi-criteria decision-making (MCDM) framework. Based on 20-year (2001-2020) Landsat 5/8 NDWI time-series analysis, 12 dams were selected from 69 candidates for detailed evaluation. Fifteen technical, climatic, and socioeconomic criteria-including solar irradiance, sunshine duration, installable FPV area, temperature, evaporation, precipitation, cloudiness, dust/hail frequency, wind speed, proximity to power grids/roads/settlements, land use, and population density-were integrated using the Best-Worst Method (BWM) for criteria weighting (consistency ratio = 0.061) and the Evaluation based on Distance from Average Solution (EDAS) for site prioritization. Expert judgments from 14 professionals yielded robust weights validated through Monte Carlo sensitivity analysis (coefficient of variation <12%, rank preservation probability >92% under +/- 20% perturbations). Results identified Dosti Dam as the top-ranked site (EDAS score = 0.997), followed by Kardeh, Chahchahe, and Toroq. The cumulative installed capacity across all 12 sites totals 2668.38 +/- 266.84 MWp, with an estimated annual energy generation of 3948.59 +/- 394.86 GWh-sufficient to meet approximately 15% of the province's current electricity demand. Economic analysis revealed a levelized cost of energy (LCOE) of 0.084/kWh (range: 0.076-0.092), approaching grid parity and expected to achieve full competitiveness within 2-3 years under current feed-in tariff escalation trends. The findings demonstrate that FPV on reservoirs represents a technically feasible, economically viable, and environmentally beneficial strategy for enhancing energy security and water resilience in semi-arid developing regions.