Snow insulation effect exceeds snowmelt in runoff regulation: Evidence from Changbai Mountain Region, China

Study region Changbai Mountain region (CMR), Northeast China, on the southern fringe of the cryosphere, is a high-precipitation area with prolonged snow cover, where runoff efficiency is particularly high during the snowmelt period. Study focus Using an enhanced Snowmelt Runoff Model (SRM) that integrates ground freeze-thaw indices (GFI/GTI) with dynamic model runoff coefficients (RC), we constructed three scenarios across five watersheds for 1990–2017: real conditions (S₀), no-snowmelt (S₁), and no-snowpack (S₂), to address the still poorly quantified relative contributions of snowpack water storage and insulation effects to runoff. New hydrological insights In the CMR, neglecting snowmelt reduced annual runoff by 2.72%, whereas omitting SIE increased annual runoff by 5.93%. Critically, SIE’s suppression effect (-5.93%) exceeded snowmelt’s positive input (+2.72%) by over twofold, demonstrating its dominant role in regulating runoff. Dramatic monthly amplifications occurred when SIE was omitted (30.05% increase in March and 23.76% in April), while the largest snowmelt-induced runoff reduction (18.46%) occurred in April under the no-snowmelt scenario. Mechanistically, SIE suppressed ground freezing through a 6.3% reduction in the GFI while enhancing thawing via a 14.9% increase in the GTI, thereby improving soil permeability and reducing runoff efficiency. These findings in CMR highlight the previously underestimated role of SIE in hydrological models and suggest that reduced snow cover may amplify runoff under future warming in seasonal frozen regions, requiring revised water resource management strategies.