Process-based modeling for mountain pasture dynamics in unusual warm and long snow-free wintertime

Katata, Genki; Grote, R.*; Zeeman, M. J.*; Mauder, M.*; Ota, Masakazu  ; Lu, H.*; Kiese, R.*

We coupled a multi-layer atmosphere-SOiL-VEGetation model (SOLVEG) with a detail snow scheme and grass growth scheme to investigate snow-free grassland dynamics. We applied the modified SOLVEG to pre-alpine grassland sites in Germany for a year with an exceptional small amount of snowfall. The modified model reproduced temporal changes in observations of surface energy and CO fluxes, soil temperature and moisture, and aboveground biomass. Our simulations and measurements demonstrate that grasses at lower elevation are not dormant and continuously assimilate atmospheric CO even in the middle of winter season. On the other hand, dead leaf biomass increases due to frosts over cold snow-free days. As a result, snow-free wintertime carbon uptake almost balanced with wintertime soil respiration. However, under temperature rise conditions, grass ecosystems act as a strong sink of CO from winter to early spring due to a decrease of frost damages of foliage.