Temporal variations in reference evapotranspiration in the Tarim River basin, Central Asia

Reference evapotranspiration (ET(0)) is important for agricultural production and the hydrological cycle. Knowledge of ET(0) can aid the appropriate allocation of irrigation water in arid regions. This study analyzed the trends in ET(0) over different timescales in the Tarim River basin (TRB), Central Asia. ET(0) was calculated by the Penman-Monteith method using data from 1960–2017 from 30 meteorological stations located in the TRB. The Mann-Kendall (MK) test with trend-free prewhitening and Sen’s slope estimator were applied to detect trends in ET(0) variation. The results showed that the mean ET(0) decreased at a rate of 0.49 mm·10 a(-1) on an annual timescale. The mean ET(0) exhibited a decreasing trend in summer and increasing trends in other seasons. The effects of climatic factors on ET(0) were assessed by sensitivity analysis and contribution rate analysis. Maximum temperature (T(max)), relative humidity (RH) and wind speed (WS) showed important effects on ET(0). However, WS, which decreased, was the key element that induced changes in ET(0) in the TRB. This work provides an important baseline for the management of agricultural water resources and scientific planning in agriculture.