Abstract: To understand the temporal and spatial variations of reference crop evapotranspiration (ET₀) in Nenjiang River Basin, and clarify the effects of climatic factors on ET₀, we calculated the daily ET₀ of each station in Nenjiang River Basin from 1970 to 2019 by Penman-Monteith formula, analyzed the temporal variation trend and spatial distribution pattern of ET₀. We further quantitatively examined the sensitivity of ET₀ to meteorological factors by sensitivity analysis, and explored the contribution of meteorological factors to ET₀ changes. The results showed that ET₀ generally showed an insignificant decreasing trend during the study period in the Nenjiang River Basin. ET₀ decreased in spring, summer, and autumn, but increased in winter, and decreased from southeast to northwest. ET₀ had the highest sensitivity to relative humidity at both temporal and spatial scales. The sensitivity coefficients of mean temperature, relative humidity and wind speed increased gradually, while that of sunshine hours decreased gradually. ET₀ was sensitive to mean temperature in northern Greater Khingan Mountains and Lesser Khingan Mountains, while to wind speed in southern Greater Khingan Mountains and Songnen Plain. Wind speed was the main factor affecting the change of ET₀ in the whole year, spring, autumn, and winter. Sunshine hours was the main affecting factor in summer. The mean temperature and relative humidity had the greatest contribution to ET₀ in the north of Greater Khingan Mountains and Lesser Khingan Mountains, and it was the wind speed in Songnen Plain.

Key words: reference crop evapotranspiration, spatio-temporal variation, sensitivity analysis, contribution rate, climatic cause, Nenjiang River Basin