A global model for the uptake of atmospheric hydrogen by soils

A simple process-based model for the consumption of atmospheric hydrogen (H-2) has been developed. The model includes a description of diffusion and biological processes which together control H-2 flux into the soil. The model was incorporated into the LPJ-WHyMe Dynamic Global Vegetation Model, and used to simulate H-2 fluxes over the 1988-2006 period. The model results have been confronted with field and laboratory measurements. The model reproduces observed seasonal cycles of H-2 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 H-2 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 H-2). 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.