Abstract: Cloud model offers a quantitative representation of the randomness and fuzziness associated with reference crop evapotranspiration (ET₀). To provide valuable insights for agricultural irrigation, flood, and drought studies in Yunnan Province, we employed cloud model to analyze the spatiotemporal distribution of ET₀ in the region based on daily meteorological data from 31 meteorological stations in Yunnan spanning the period from 1958 to 2013. ET₀ was calculated and examined using linear trend, partial correlation analysis, and the M-K methods. Results revealed a lack of consistency in the homogeneity of the temporal-spatial distribution of ET₀ in Yunnan. The temporal variation exhibited lower homogeneity and stability compared to the spatial distribution. Over the 56 years, no significant increasing trend in ET₀ was observed. However, after the year 2000, a significant upward trend in ET₀ became evident, accompanied by a decrease in homogeneity and stability. Seasonally, spring exhibited the highest ET₀, while winter displayed the lowest values. Notably, ET₀ distribution in winter and spring appeared uneven and unstable. Spatially, the middle and south region exhibited higher ET₀ values than the eastern and western and northern areas. Further analysis highlighted an increasing trend in ET₀ in western Yunnan, while the middle and eastern regions experienced a decrease. The high-value areas in central Yunnan exhibited uneven and unstable variations in ET₀. Additionally, our analysis identified humidity, sunshine duration, and wind speed as the primary influencing factors on ET₀.

Key words: evapotranspiration, reference crop, influencing factors, spatial and temporal variations, cloud model, Yunnan Province