Evidence of Vertical Soil Hydraulic Heterogeneity Regulating Hydrothermal Simulations in Qinghai–Tibetan Plateau Wetlands

Abstract. Alpine wetlands on the Qinghai-Tibetan Plateau host vertically structured and highly contrasting pore systems that fundamentally shape land and atmosphere exchanges, yet their hydraulic expressions and process implications remain poorly quantified. This study provides the first process based and depth resolved characterization of these layered pore structures using soil physical analyses and laboratory evaporation experiments. The derived Clapp–Hornberger parameters reveal coherent hydraulic contrasts, with surface layers dominated by macropore connectivity and showing high θs and Ks and low b that promote rapid drainage and evaporation, mid layer domains with lower θs and Ks and larger b that enhance retention in finer pores, and deeper layers that act as stable and persistent storage reservoirs. These properties together generate a vertical regime of rapid near surface drainage, delayed mid layer release, and long lasting deep moisture storage. When implemented in Noah-MP, this hydraulic stratification systematically altered water and energy partitioning during wet and dry periods and showed that vertical hydraulic heterogeneity rather than a single layer parameterization governs the timing and magnitude of evaporation and heat fluxes. These findings provide the first quantitative evidence that pore scale structure regulates profile scale hydrothermal responses in Qinghai-Tibetan Plateau wetlands and establish a physically grounded basis for representing vertically heterogeneous hydraulic processes in land surface models.