Prediction of reference crop evapotranspiration with grey model in Xinjiang region

Based on daily meteorological observation data of six stations in Xinjiang region, Penman-Monteith equation was used to calculate daily reference crop evapotranspiration(ET0). The rescaled range analysis method was applied to analyze future tendency of annual ET0. Grey relational theory was used to calculate the correlation degree and order between meteorological factors and annual ET0 for each station. Based on that, grey information renewal GM(1, h) model of unequal dimensions which was established by the grey systematic theory was used to simulate and predict annual ET0 of the six stations, and GM(1, h) model was compared with it. The results showed that the tendency of month ETo was parabola, and the sequence of ET0 variation with month was Ruoqiang > Tulufan > Hami > Kashi > Hetian > Yining, respectively. From April to September, the Hurst indice of annual ET0 in six stations were all larger than 0.5, the future tend of stations were still volatility decreasing which were positively related to their history. In general, the annual ET0 values of various stations were mostly affected by average temperature, sunshine hours, saturated pressure difference. The relative error limits for the predictions using grey information renewal GM(1, h) model of unequal dimensions ranged from 0 to 7.31%, with obviously high accuracy of prediction than GM(1, 1) model. This study shows that accuracy of predicting reference crop evapotranspiration in Xinjiang region is relatively good.