INCORPORATING SEASONALLY VARYING SURFACE ORGANIC LAYER INTO VERSION 4 OF THE COMMUNITY LAND MODEL

Organic material plays an important role in surface energy partitioning due to its distinct thermal and hydraulic properties compared to mineral soil. Although most of soil in a temperate deciduous forest and deciduous grass is covered by a shallow litter layer during dormant period, it is not considered properly in land surface models. CLM4 considers the effect of seasonally varying litter indirectly using radiative effect of dead standing grass (SAI) which increases after litterfall and decreases linearly during dormant period. In this study, we removed radiative effect of dead standing grass and incorporated a seasonally varying shallow litter layer above the mineral soil in CLM4 and scrutinized the simulated surface fluxes and soil temperature and moisture against the in-situ observation data over a Tibetan grassland. The litter depth is parameterized to increase right after litterfall and then decrease with time. The moisture of litter layer is parameterized to increase with intercepting rainfall and to decrease with evaporation. Preliminary results show that incorporation of the shallow organic layer shows improvement of underestimation of soil temperature and sensible heat flux during winter. However, it prevents rapid warming of soil during spring. Other problems and difficulties in the parameterization are also discussed.