Evaluation of meteorological factors influencing reference crop evapotranspiration based on different methods of mathematical statistics in Henan province

Abstract: To determine the main meteorological factors affecting the inter-annual variability of ET0 is the basis of accurate estimation of crop water requirement in the future, and is also of great significance in dealing with the climate change for agricultural production. In this paper, we investigated the factors affecting reference crop evapotranspiration (ET0) based on different mathematical statistic methods in Henan province. The evaluation results from the different methods were compared with the actual variation trend of ET0 and each factor. The effective method should be consistent with the trend. From common methods, we selected 5 methods to evaluate the effects of 7 meteorological factors on the inter-annual variability of ET0 based on the meteorological data of 17 stations in Henan province. The 5 methods included the correlation method, partial correlation method, dominant method, stepwise regression analysis, grey correlation analysis based on numerical average, numerical initial and numerical standardization data. The data were on the highest temperature, the lowest temperature, average temperature, relative humidity, precipitation, wind speed and sunshine hours. They were from meteorological stations. The annual average of daily ET0 was calculated by the Penman-Monteith method. The result showed that the influential factors based on the 5 methods were different for each station. By considering the trend of ET0 and each factor during a long term, we obtained the main factors affecting ET0 in Henan. The sunshine was the primary factor for Shangqiu, Xuchang, Lushi, Xixia, Nanyang, Zhumadian, Xinyang, and Gushi stations. The wind speed was the primary factor for Anyang, Xinxiang, Kaifeng, Zhengzhou, Luanchuan and Mengjin station. In the other stations, sunshine and wind speed were both the primary factor. In sum, the sunshine and wind speed were the main factors affecting reference crop evapotranspiration in Henan province, the average wind speed was more important than the other factors in the northern region of the Yellow River, but the sunshine was more important in the southern area of the Yellow River. The impact of the high temperature could not be ignored in the estimation of ET0 at Xinyang and Xixia stations. There were great differences in evaluation results among 5 methods. Grey correlation analysis method was not suitable for the evaluation of the main factors influencing ET0 variation because of the different results with different data transformation. Stepwise regression analysis was not suitable either because there were many differences between actual and prospective trend of ET0 based on the change trend of meteorological elements in each station. Correlation analysis, partial correlation analysis and dominant analysis were suitable to determine the main factors influencing ET0 variation in a given area with small difference in its conclusion and uniform results. Furthermore, dominant analysis method was adopted to rank meteorological factors influencing ET0 variation and its actual ET0 was consistent with the predicting trend of ET0, so it can be used to evaluate the sequence of meteorological factors affecting ET0 changes in each station. However, the dominant method should be assisted by the results from the correlation and partial correlation method since it could not obtain the correlation between ET0 and each factor. It was suggested that correlation analysis and partial correlation analysis method could be adopted to analyze the relationship between each factor and ET0 in order to get credible results.