Hot spots of soil moisture variations (HSSM) within a catchment are areas exhibiting significant fluctuations in soil moisture, which critically influence soil moisture organization, soil re-oxygenation, and soil carbon export. However, current methods for identifying HSSM have been inefficient under decreasing soil moisture conditions and remain unvalidated in complex terrains. This study introduces an enhanced soil moisture variation index (ESMVI) that measures the relative change in soil moisture per unit time interval. It is designed to detect abrupt changes during both increasing and decreasing soil moisture phases while considering initial soil moisture conditions. We utilized the 95th percentile threshold of ESMVI to improve HSSM identification in areas with high soil moisture variability and complex terrain. We collected a 3-year (2011–2014) continuous daily soil moisture dataset from a sensor network comprising 33 monitoring sites in a headwater catchment. To evaluate the enhanced protocol’s effectiveness, we calculated the ratio of HSSM to all monitoring sites during rising and falling soil moisture phases across various soil horizons. Furthermore, we analyzed the spatiotemporal patterns of the identified HSSM to explore their potential mechanisms under varying hydrological and terrain conditions. Our findings demonstrate that, compared to the established protocol, (1) the enhanced protocol increased the ratio of HSSM from 0–13 % to 16–24 %, thereby improving the representation of the spatial variability in HSSM during falling soil moisture periods; and (2) the spatial patterns of HSSM derived from the enhanced protocol showed a stronger correlation with local hydropedological attributes across the catchment. For example, when precipitation exceeded 10 mm, approximately 23 % of HSSM shifted from swale to slope sites in Horizons A and B. In contrast, Horizon C exhibited about 56 % of HSSM concentrated on the north-facing aspect, maintaining a steady-state pattern. This suggests that the hydrological thresholds for HSSM occurrence vary with soil depth. This study underscores the potential of the enhanced protocol to deepen our understanding of the mechanisms driving soil moisture variations in headwater catchments, providing a more accurate approach to identifying and analyzing HSSM.

中文翻译：

---

增强对源头集水区土壤水分变化热点的识别


集水区内土壤水分变化 （HSSM） 的热点是土壤水分波动显著的区域，这些波动对土壤水分组织、土壤再氧化和土壤碳输出产生重大影响。然而，目前识别 HSSM 的方法在土壤湿度降低的条件下效率低下，并且在复杂地形中仍未得到验证。本研究引入了增强型土壤水分变化指数 （ESMVI），用于测量每单位时间间隔土壤水分的相对变化。它旨在检测土壤水分增加和减少阶段的突然变化，同时考虑初始土壤水分条件。我们利用 ESMVI 的第 95 个百分位阈值来改进土壤水分变化高和地形复杂地区的 HSSM 识别。我们从由源头集水区的 33 个监测点组成的传感器网络收集了 3 年 （2011-2014） 连续的每日土壤水分数据集。为了评估增强协议的有效性，我们计算了在不同土壤水平上土壤水分上升和下降阶段 HSSM 与所有监测站点的比率。此外，我们分析了已识别的 HSSM 的时空模式，以探索它们在不同水文和地形条件下的潜在机制。我们的研究结果表明，与已建立的方案相比，（1） 增强方案将 HSSM 的比率从 0-13 % 增加到 16-24 %，从而改善了土壤水分下降期间 HSSM 空间变化的表示;（2） 从增强协议得出的 HSSM 空间模式与整个集水区的当地水生土壤属性显示出更强的相关性。 例如，当降雨量超过 10 毫米时，大约 23% 的 HSSM 从洼地转移到地层 A 和 B 的斜坡站点。相比之下，层面 C 表现出约 56% 的 HSSM 集中在朝北的侧面，保持稳态模式。这表明 HSSM 发生的水文阈值随土壤深度而变化。这项研究强调了增强协议的潜力，以加深我们对驱动源头集水区土壤水分变化机制的理解，为识别和分析 HSSM 提供更准确的方法。