Bedrock moisture dynamics in humid karst hillslopes: A storage-response trade-off governed by weathering intensity

<jats:p>Bedrock moisture is a critical yet insufficiently understood component of the hydrological cycle, particularly in karst regions where shallow soils overlie weathered bedrock. This study investigated how structure influences bedrock hydrology on two hillslopes with contrasting weathering characteristics within a humid karst catchment, across two hydrologically years&amp;mdash;an extreme wet year (2020, 2245 mm) and a normal year (2021, 1325 mm). The normalized bedrock moisture index (NBMI) was derived from high-resolution volumetric water content at five depths across a strongly weathered hillslope (SWH) and a weakly weathered hillslope (WWH). Results show that WWH maintained higher NBMI than SWH (34.5% vs. 23.0%), with a smaller dry-season decline. Moreover, WWH exhibited a higher response rate to rainfall (66&amp;ndash;87% vs. 56&amp;ndash;76%) and a 1.3 to 2.6 times larger water retention area than SWH. These findings indicate that WWH exhibited superior moisture availability, recharge efficiency, and effective water storage. Furthermore, despite extreme rainfall in 2020, SWH dried rapidly during the subsequent dry season, whereas WWH retained higher moisture even in the normal year. Wavelet analysis further reveals that WWH exhibits stronger power at the 16&amp;ndash;64 day period, reflecting its rapid response to rainfall. In contrast, SWH is dominated by seasonal cycles exceeding 64 days, indicating that its moisture dynamics are primarily controlled by long-term precipitation patterns. Collectively, these findings reveal a storage-recharge trade-off: WWH excels in recharge and moisture via rainfall sensitivity, while SWH stores more yet stays underfilled from limited recharge&amp;mdash;offering insights into bedrock moisture in soil-limited karst.</jats:p>