Correspondence Mehdi Rahmati, Dep. of Soil Science and Engineering, Faculty of Agriculture, Univ. of Maragheh, Maragheh, Iran. Email: mehdirmti@gmail.com Harry Vereecken, Agrosphere Institute IBG3, Forschungszentrum Jülich, 52425 Jülich, Germany. Email: h.vereecken@fz-juelich.de Abstract Weighable lysimeters were used to study the relation between soil water content (SWC) and the actual evapotranspiration (ETa) of grassland under two different climate regimes of Rollesbroich and Selhausen but for an identical soil from Rollesbroich. All components of the water balance were determined from 2012 until 2018. Budyko analysis was used to characterize the hydrological status of the studied sites. Wavelet analysis was also applied to study the power spectrum of ETa, vegetationheight-adjusted reference evapotranspiration (ETcrop), and water stress index (WSI) defined as ETa/ETcrop, as well as SWC at three different depths and the coherence between SWC and ETa and WSI. The Budyko analysis showed that 2018 resulted in a shift of both locations towards more water-limited conditions, although Rollesbroich remained an energy-limited system. Based on the power spectrum analysis, the annual timescale is the dominant scale for the temporal variability of ETa, ETcrop, and SWC. The results also showed that increasing dryness at the energy-limited site led to more temporal variability of SWC at all depths at the annual timescale. Wavelet coherence analysis showed a reduction of the phase shift between SWC and ETa at an annual scale caused by the increase in dryness during the measurement period. We found that phase shifts between SWC and ETa and SWC and WSI were stronger at the water-limited site than at the energy-limited site. The wavelet coherence analysis also showed that from 2014 to 2018, the control of ETa and WSI on SWC increased due to higher dryness of soil.

中文翻译：

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干旱加剧对草地土壤含水量与蒸散量关系的影响

通讯 Mehdi Rahmati，Dep。土壤科学与工程学院，农业学院，大学。马拉盖，马拉盖，伊朗。电子邮件：mehdirmti@gmail.com Harry Vereecken，Agrosphere Institute IBG3，Forschungszentrum Jülich，52425 Jülich，德国。电子邮件：h.vereecken@fz-juelich.de 摘要 使用可称重蒸渗仪研究了在 Rollesbroich 和 Selhausen 两种不同气候条件下但对于相同土壤的草地土壤含水量 (SWC) 与实际蒸散量 (ETa) 之间的关系来自罗尔斯布罗赫。从 2012 年到 2018 年确定了水平衡的所有组成部分。 Budyko 分析用于表征研究地点的水文状况。小波分析还用于研究 ETa 的功率谱、植被高度调整后的参考蒸发量 (ETcrop)、和定义为 ETa/ETcrop 的水分胁迫指数 (WSI)，以及三个不同深度的 SWC 以及 SWC 与 ETa 和 WSI 之间的一致性。Budyko 的分析表明，2018 年导致两个地点都转向了更加缺水的条件，尽管 Rollesbroich 仍然是一个能源受限的系统。根据功率谱分析，年时间尺度是ETa、ETcrop和SWC时间变化的主导尺度。结果还表明，能量受限地点的干燥度增加导致年度时间尺度上所有深度的 SWC 的时间变化更大。小波相干分析表明，由于测量期间干燥度的增加，SWC 和 ETa 之间的相移在年尺度上有所减少。我们发现 SWC 和 ETa 以及 SWC 和 WSI 之间的相移在水限制位置比在能量限制位置更强。小波相干分析还表明，2014-2018 年，由于土壤干燥度较高，ETa 和 WSI 对 SWC 的控制增加。