A global model for the uptake of atmospheric hydrogen by soils

A simple process-based model for the consumption of atmospheric hydrogen (H₂) has been developed. The model includes a description of diffusion and biological processes which together control H₂ flux into the soil. The model was incorporated into the LPJ-WHyMe Dynamic Global Vegetation Model, and used to simulate H₂ fluxes over the 1988-2006 period. The model results have been confronted with field and laboratory measurements. The model reproduces observed seasonal cycles of H₂ uptake at different sites and shows a realistic sensitivity to changes in soil temperature and soil water content in comparisons with field and laboratory measurements. A recent study, based on 3D atmospheric model inversion, found an increase of the global H₂ sink from soils, with a trend of -0.77 Tg a^-2 for the 1992-2004 period (fluxes are negative as soils act as a sink for atmospheric H₂). For the same period, however, our process-based model calculates a trend of only -0.04 Tg a^-2. Even when forced with drastic changes in soil water content, soil temperature and snow cover depth, our model is unable to reproduce the trend found in the inversion-based study, questioning the realism of such a large trend.