Influence of climate change on reference evapotranspiration and aridity index and their temporal-spatial variations in the Yellow River Basin, China, from 1961 to 2012

The non-parametric Mann-Kendall method, wavelet transform and simple linear regression were applied in this study to investigate the temporal trends and spatial distributions for reference evapotranspiration and aridity index in the Yellow River Basin, China, from 1961 to 2012. The key meteorological factors for ET0 and AI were also evaluated. The results showed that the annual mean ET0 had a significant declining trend at the rate of 1.29 mm per year and AI also had a slightly decreasing trend of 0.001 per year from 1961 to 2012. The abrupt change used by the M−K method revealed that the year of abrupt change for ET0 was in 1983 and 1993, but AI did not have abrupt change from 1961 to 2012. The spatial distributions of the average annual ET0 exhibited a declining trend from northeast to southwest over the study region. The spatial change trends for AI were similar to ET0, which the decreasing trends were located in the most parts of YRB. Furthermore, the correlation coefficient analysis indicated that the change of sunshine hours was the major factors influencing the variability of ET0, followed by wind speed. However, the dominating factor of AI was relative humidity, followed by precipitation. The significant wavelet power spectra of ET0 were 4-6 year and 12-15 year and there were obvious periodic oscillations of 4-6 year, 8-12 year and 18-22 year for AI. The periodic variation of ET0 was similar in some degree with that of AI and both of them had the comparable main periods.