Variations in hillslope soil moisture control forest hydrologic fluxes and storage pools, yet sparse observations combined with the complexity and heterogeneity of water movement and storage in the vadose zone can make temporal and spatial patterns and processes difficult to predict. We used two years of field observations of volumetric soil moisture at three depths (15, 30, and 100 cm) across five topographic positions (riparian, toeslope, sideslope, shoulder, and ridge) along three hillslope transects to better understand how soil moisture changes with hillslope position and through time. As expected, we found higher values of soil moisture at all depths at the riparian and toeslope positions. Unexpectedly, we found that ridges were particularly wet during the wet winter months and dried quickly during the summer months, indicating that topography alone cannot account for mean wet season soil moisture in our Mediterranean climate field site. The variability in soil moisture across all soil depths and topographic positions was greatest when soils were dry and decreased under wet soil conditions; this variability remained high in the deeper soil horizons, regardless of season. Lastly, event analysis suggests that the response to early season rainfall was highly variable along the hillslopes and was likely dominated by localized controls such as microtopography and vegetation as well as soil texture, antecedent moisture conditions, and rainfall characteristics. Our results suggest that the drivers of wet and dry season soil moisture dynamics can vary across topographic positions along a hillslope and do not always follow topographic controls.

中文翻译：

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地中海山地流域的动态山坡土壤水分

山坡土壤水分的变化控制着森林水文通量和蓄水池，但稀疏的观测加上包气带中水运动和蓄水的复杂性和异质性，可能使时空格局和过程难以预测。我们对沿三个山坡横断面的五个地形位置（河岸、坡脚、边坡、肩部和山脊）的三个深度（15、30 和 100 厘米）的体积土壤水分进行了两年的实地观察，以更好地了解土壤水分是如何变化的与山坡位置和时间。正如预期的那样，我们发现河岸和坡脚位置所有深度的土壤水分值都较高。出乎意料的是，我们发现山脊在潮湿的冬季特别潮湿，而在夏季干燥得很快，表明仅靠地形不能解释我们地中海气候现场的平均湿季土壤湿度。当土壤干燥时，所有土壤深度和地形位置的土壤水分变化最大，而在潮湿土壤条件下则减少；无论季节如何，这种变化在更深的土壤层中仍然很高。最后，事件分析表明，沿山坡对早季降雨的响应变化很大，可能主要受局部控制因素的影响，如微地形和植被以及土壤质地、前期水分条件和降雨特征。我们的结果表明，湿季和旱季土壤水分动态的驱动因素可能会因山坡上的地形位置而异，并且并不总是遵循地形控制。