Reference evapotranspiration (ET0) is critical for understanding hydrological cycles and optimizing agricultural water management. This study analyzed spatiotemporal trends in ET0 and its driving meteorological variables including air temperature (T), relative humidity (RH), net radiation (RN), wind speed (U), across the Yellow River Basin from 1970 to 2024, utilizing data from 309 stations. The methodologies employed included Mann-Kendall tests, multifractal detrended fluctuation analysis (MFDFA), sensitivity analysis, and contribution analysis. Annual ET0 showed a nonsignificant decreasing trend, with high values concentrated in the midstream regions (e.g., Loess Plateau) and low values in the downstream and upstream areas. The MFDFA analysis revealed that T and ET0 exhibit the widest range of scaling exponents (Delta h(q)), thereby confirming their significant multifractal characteristics. Sensitivity analysis identified RH as the primary driver, but contribution analysis revealed U as dominant factor due to its substantial variability. The decline in ET0 was attributed to reduced U and RN, illustrating the "evaporation paradox", where high-sensitivity factors may contribute less than variables with greater trend magnitude. The framework of integrating trend, multifractal, and attribution analyses offers transferable insights for ET0 modeling in other arid/semi-arid basins globally.