Abstract Actual evaporation (Ea) can be calculated as a fraction of potential evaporation (PE), which refers to the evaporation rate if supply water is unlimited. Potential evaporation depends on the available energy and the underlying material, and different approaches to estimate potential evaporation exist nowadays. This study provides a detailed analysis of the evaporation dynamics over fully saturated, sandy soil (PEs) and an open water surface (PEw). Moreover, the performance of commonly used methods to estimate PE is assessed. At the basis of these analyses is a lysimeter experiment in the Guanzhong Basin, which allowed a precise measurement of PE with a very high temporal resolution. Temperature profiles in lysimeters and meteorological data were also measured during the experiment. A comparison of PEs and PEw was carried out for seven consecutive days (August 11th to 17th , 2016). Results show that PEw is smaller than PEs on a daily scale, with PEw rates being bigger than PEs at night but smaller during daytime. Furthermore, the temporal dynamics of PEw lags 4-5 hours behind PEs. In accordance with the energy balance equation, PE dynamics are mainly governed by “available energy”. The PE rates calculated by Penman-Monteith (PM) and Priestly-Taylor (PT) based on these measurements were also evaluated. The measured PE is relatively well reproduced by PM and PT equations. Finally, the effect of using different approaches to estimate PE on calculating Ea was tested by an integrated hydrological model that calculates water flow in the unsaturated zone by solving the Richards equation. The absolute value of relative differences were up to 17.5 %.

中文翻译：

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饱和裸土和开阔水面的潜在蒸发动力学

摘要 实际蒸发量 (Ea) 可以计算为潜在蒸发量 (PE) 的一部分，这是指在供水不受限制的情况下的蒸发率。潜在蒸发取决于可用能量和底层材料，现在存在不同的估算潜在蒸发的方法。本研究详细分析了完全饱和的沙质土壤 (PE) 和开阔水面 (PEw) 上的蒸发动态。此外，还评估了常用的 PE 估计方法的性能。这些分析的基础是关中盆地的蒸渗仪实验，它允许以非常高的时间分辨率精确测量 PE。实验期间还测量了蒸渗仪中的温度分布和气象数据。连续 7 天（2016 年 8 月 11 日至 17 日）对 PEs 和 PEw 进行了比较。结果表明，PEw 在日常规模上小于 PE，PEw 比率在夜间大于 PE，但在白天较小。此外，PEw 的时间动态比 PE 滞后 4-5 小时。根据能量平衡方程，PE 动力学主要受“可用能量”控制。还评估了 Penman-Monteith (PM) 和 Priestly-Taylor (PT) 根据这些测量结果计算的 PE 率。测得的 PE 相对较好地由 PM 和 PT 方程再现。最后，通过求解理查兹方程来计算非饱和带中的水流量的集成水文模型测试了使用不同方法估计 PE 对计算 Ea 的影响。