Abstract Physically, evaporative demand is driven by net radiation ( R n ), vapour pressure ( e a ), wind speed ( u 2 ), and air temperature ( T a ), each of which changes over time. By analyzing temporal variations in reference evapotranspiration (ET 0 ), improved understanding of the impacts of climate change on hydrological processes can be obtained. In this study, variations in ET 0 over 58 years (1950–2007) at 34 stations in the Haihe river basin of China were analyzed. ET 0 was calculated by the FAO Penman–Monteith formula. Calculation of Kendall rank coefficient was done by analyzing the annual and seasonal trends in ET 0 derived from its dependent climate variables. Inverse distance weighting (IDW) was used to analyze the spatial variation in annual and seasonal ET 0 , and in each climate variable. An attribution analysis was performed to quantify the contribution of each input variable to ET 0 variation. The results showed that ET 0 gradually decreased in the whole basin over the 58 years at a rate of −1.0 mm yr −2 , at the same time, R n , u 2 and precipitation also decreased. Changes in ET 0 were attributed to the variations in net radiation (−0.9 mm yr −2 ), vapour pressure (−0.5 mm yr −2 ), wind speed (−1.3 mm yr −2 ) and air temperature (1.7 mm yr −2 ). Looking at all data on a month by month basis, we found that T a had a positive effect on dET 0 /d t (the derivative of reference evapotranspiration to time) and R n and u 2 had negative effects on dET 0 /d t . While changes in air temperature were found to produce a large increase in dET 0 /d t , changes in other key variables each reduced rates, resulting in an overall negative trend in dET 0 /d t .