Spatiotemporal variability of reference evapotranspiration over the Northeast region of China in the last 60 Years

Based on the daily meteorological measurements of 106 meteorological stations in Northeast China from 1951 to 2007,the daily reference evapotran spiration (ET₀) and yearly ET₀ are estmiated using the Penman-Monteith equation1 Gridded annual and annual-average ET₀ values for the region are produced using the inverse distance weighted interpolation method.The spatiotemporal variability of ET₀ is analyzed using the methods of Mexican hat wavelet transform,Mann-Kendall test,the rotated empirical orthogonal function,and the inclination rate.The results show that:(1) a slightly increasing trend (3.89 mm/10a) is detected in the regional-average ET₀ tmie series,and the regional ET₀ minmium and maxmium are found in 1953 and 1982,respectively; (2) the temporal variability of regional-average ET₀ has a quasi-periodicity of 8216 years experiencing four alternating stages (low-high-low-high),and in which an intensified ET₀ oscillation of 8210 years is observed; (3) the annual-average ET₀ ranges from 600 mm to 1.60 mm,and appears as obviously spatial difference exhibiting semiring-shaped isogramswith a gradual ET₀ increment from Northeast to Southwest; and (4) the annual-average ET₀ shows a increase trend over 72161% of the region doma in based on the analysis of inclination rate,while the opposite result is obtained for the rest of the region; the maxmium and minmium values of inclination rate are 3016 mm/10a at Nenjiang station and 224.4 mm/10a at Yebaishou station,respectively.