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Analyses of the spatial and temporal variation of reference evapotranspiration (ET 0 ) and aridity index (AI) can further understand climate change and its effect on hydrology. In this study, based on date from 58 standard meteorological stations, the spatio-temporal variations and trends of ET 0 and AI were calculated for the Loess Plateau Region (LPR) from 1961 to 2012 using the Mann–Kendall test, the moving t -test, and the Morlet wavelet methods. The results demonstrated: (1) the annual ET 0 displayed a statistically significant decrease of −10.3 mm/10 y ( P < 0.05) during 1961–2012. At that time, AI also had a decreasing trend of −0.013/10 y over the past 52 years. Compared with ET 0 , the inter-decadal variations of AI over the LPR seemed to show similar declined trends. (2) Spatially, about 81% stations displayed a decreasing trend for annual ET 0 during 1961–2012, and most of them were distributed in the western, northern and southeastern LPR. In addition, about 60% of stations showed statistically decreasing trends for AI, and the major decreases were mainly in the east Qinghai division and northern LPR. (3) Abrupt changes were detected in annual ET 0 series in the 1980s and in annual AI series in 1987. Wavelet analysis indicated significant 2 year and non-significant 7, 10 and 14 years in annual ET 0 series, and there existed periods of 4, 8 and 12 years for AI. (4) For ET 0 , wind speed was the most sensitive meteorological factor, followed by sunshine hours, precipitation, and relative humidity. For AI, ET 0 and precipitation were the sensitive factors. This study provides an understanding of the effect of recent climate change on hydrological cycle in the LPR. [ABSTRACT FROM AUTHOR]