Exploring the variance in reference evapotranspiration (ET₀) and its dominant influencing factors is important for climate change, hydrological cycles and water management. Temperature (T), wind speed (U₂), net radiation (R_n) and actual vapour pressure (e_a) are the major climatic input variables in Penman–Monteith equation. Previous studies have successfully applied the total differential method to determine the relative contributions of changes in these variables to variation in ET₀ on different timescales. However, the interaction of climatic variables has not been incorporated into this method. Taking the inland river basin of Northwest China as the study area, we extended the total differential method to decompose the ET₀ variance into temporal variance and covariance of T, U₂, R_n and e_a on intra-annual and annual scales during 1960–2017. The results indicated that the variance in ET₀ on the intra-annual scale was larger than that on the annual scale. Among the four single climatic variables, U₂ variance made larger contributions to intra-annual and annual ET₀ variance with relative contributions of 6.8% and 1.1%, respectively. However, the interaction of climatic variables played a dominant role in the variation in ET₀. Specifically, on intra-annual scale, coupled U₂ and R_n primarily controlled the ET₀ variance (76.1%), followed by coupled R_n and e_a (9.6%); but their positive effects were weakened by the negative effects of coupled T and e_a (−2.3%). On annual scale, coupled U₂ and R_n still governed the variance in ET₀ (97.3%), but the effects were also weakened by other groups of interaction effects. Furthermore, ET₀ was highly related to NDVI on an intra-annual scale (R² = 0.68, p = 0.00), indicating the strong effect of seasonal vegetation dynamics on ET₀ variance. This study provides new insights to quantitatively assess the interaction effects of environmental factors on key hydrometeorological variables.

中文翻译：

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风速与净辐射相互作用控制西北内陆河流域参考蒸散量变化

探索参考蒸散量（ET ₀）的变化及其主要影响因素对于气候变化、水文循环和水资源管理具有重要意义。温度 ( T )、风速 ( U ₂ )、净辐射 ( R _n ) 和实际蒸气压 ( e _a ) 是 Penman-Monteith 方程中的主要气候输入变量。以前的研究已经成功地应用了总微分法来确定这些变量的变化对 ET _{0变化的相对贡献}在不同的时间尺度上。然而，气候变量的相互作用尚未纳入该方法。以西北内陆河流域为研究区，扩展全微分法，将1960年ET ₀方差分解为T、U ₂、R _n和e _a在年内和年尺度上的时间方差和协方差–2017 年。结果表明，ET ₀在年内尺度上的方差大于在年尺度上的方差。在四个单一气候变量中，U _{2方差对年内和年 ET 0}的贡献较大方差分别为 6.8% 和 1.1%。然而，气候变量的相互作用在ET ₀的变化中起主导作用。具体而言，在年内尺度上，耦合的U ₂和R _n主要控制 ET ₀方差（76.1%），其次是耦合的R _n和e _a（9.6%）；但它们的积极影响因耦合T和e _a (-2.3%) 的负面影响而减弱。在年度尺度上，耦合的U ₂和R _n仍然控制着 ET _0的方差(97.3%)，但其他组的交互作用也削弱了这些作用。此外，ET ₀在年内尺度上与NDVI高度相关（R ²  = 0.68，p  = 0.00），表明季节性植被动态对ET ₀方差的影响很大。本研究为定量评估环境因素对关键水文气象变量的相互作用提供了新的见解。