Problems associated with water scarcity are facing new challenges under the climate change. As one of main consumptions in water cycle on the Earth, evapotranspiration plays a crucial role in regional water budget. In this paper, we employ two methods, i.e. hydrological sensitivity analysis and hydrological model simulation, to investigate the effect of climate variability and climatic change on actual evapotranspiration (E_a) within the Laohahe basin during 1964–2009. Calibrations of the two methods are firstly conducted during the baseline period (1964–1979), then with the two benchmarked models, simulations in climatic change duration (1980–2009) are further conducted and quantitative assessments on climatic change-induced variation of E_a are analysed accordingly. The results show that affected by combined impacts of decreased precipitation and potential evapotranspiration, variation of annual E_a in most sub-catchments suffer a downward trend during 1980–2009, with a higher descending rate in northern catchments. At decadal scale, E_a shows significant oscillation in accordance with precipitation patterns. Northern catchments generally suffer more decadal E_a changes than southern catchments, implying the impact of climatic change on decadal E_a is more intense in semi-arid areas than that in semi-humid regions. For whole changed durations, a general 0–20 mm reduction of E_a is found in most parts of studied region. For this water-limited region, E_a shows higher sensitivity to precipitation than to potential evaporation, which confirms the significant role of precipitation in controlling E_a patterns, whereas the impact of potential evapotranspiration variation would be negligible.