Quantitative estimation of the impact of climate change on actual evapotranspiration in the Yellow River Basin, China

The spatial distribution and temporal trends for actual evapotranspiration (ETa) reflect the combined effects of the climate, soil and vegetation. This study was conducted to investigate the influence of climatic change on ETa. Using the simple two-parameter steady-state model (SPS model), ETa was calculated from precipitation and potential evapotranspiration (ETp) at 89 meteorological stations during 1961–2006 in the Yellow River Basin (YRB), China. The spatial distribution of ETa was performed by means of Kriging method, and the temporal trends of ETa were investigated by the least squares linear model (linear fitted model), the Mann–Kendall method (the M–K method), Kendall τ statistical method (Kendall τ method) and the causes for the variations were discussed by means of the ‘detrended method’ and SPS model. The results presented that: (i) the spatial distribution of ETa, as most of the YRB is water-limited, presented a similar spatial pattern with precipitation, which demonstrates decreasing trends from southeast to northwest; (ii) negative trends for ETa were detected by both the linear fitted model and Kendall τ method, and significant decreasing trends (at 95% confidence level) were detected in all regions of YRB; (iii) the timings of abrupt changes detected by the M–K method was 1991, 1979, 1975 and 1978 in the upper, middle, lower region and whole YRB, respectively, and so the ETa during 1961–2006 was divided into two periods: natural period and changed period (e.g. natural period (1961–1990) and changed period (1991–2006) in the upper region); and (iv) the influence of climatic change on ETa contributed to −3.10 × 109 m3, −4.26 × 109 m3, −15.68 × 109 m3 and −16.62 × 109 m3 between natural period and changed period in the upper region, middle region, lower region and whole basin of YRB, respectively. The trends of ETa, ETp and precipitation reflected that ETa is controlled by precipitation rather than ETp, especially the results presented an evidence for the Bouchet’s complementary hypothesis in the middle region of YRB.