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Soil moisture thresholds for runoff generation: depth sensitivity and mechanistic controls

Year: 2026
Type: article
Abstract: A compound wetness index combining antecedent soil moisture and event rainfall (S 0 = ASI 0 + P) is commonly used to analyze threshold-based runoff responses. However, it remains unclear how the depth of soil moisture integration affects threshold detection and predictive performance. Here, we examined the relationship between runoff thresholds and maximum integration depth (MID) across four experimental catchments spanning diverse climates and runoff generation mechanisms. Using segmented regression across multiple MIDs and monitoring sites, we identified runoff thresholds and evaluated the explanatory power of S 0 for stormflow using post-threshold coefficients of determination (R h 2 ). Thresholds were consistently detected across integration depths, but explanatory power varies strongly among catchments. In storage-controlled systems, R h 2 increased with depth, indicating that deeper soil moisture integration better captured subsurface storage controls on stormflow initiation. In contrast, in connectivity-limited or shallow flow-dominated systems, shallow integration depths performed better because near-surface wetting controlled preferential flow or infiltration-excess runoff, whereas deeper integration included hydrologically inactive storage. These results show that the optimal integration depth is catchment dependent and closely linked to dominant runoff generation processes. Accounting for this depth dependence can improve threshold-based runoff analysis and support more process-consistent soil moisture monitoring and hydrological modeling
DOI: 10.1016/j.jhydrol.2026.135827
Institution: Tsinghua University
Language: English
Open Access status: hybrid
Estimated APC paid: $4,030
OpenAlex ID: W7163349752
FWCI: 7.514
Cites: 33
Cited by: 5
Related to: 10