Here is a concise summary of the article:

## Computation of Surface Mass Balance (SMB)

The article describes how the Community Land Model (CLM) computes the surface mass balance (SMB) for glaciers and ice sheets, specifically in Greenland and Antarctica.

Key points:

- SMB is the net annual accumulation/ablation of mass at the surface of a glacier or ice sheet. Accumulation is primarily from snowfall, while ablation is from melting and evaporation/sublimation.

- CLM uses a surface-energy-balance (SEB) scheme to compute SMB, where melting depends on the radiative, turbulent, and conductive fluxes at the surface.

- The SMB flux passed to the ice sheet model (CISM) is the mass balance for ice alone, not snow.

- The handling of SMB and runoff fluxes depends on whether CISM is evolving in two-way-coupled mode (_glc_dyn_runoff_routing_).

- If CISM is not evolving, the snow capping flux is added to the ice runoff flux, with a reduction to account for conservation.

- If CISM is evolving, the snow capping flux is not counted as runoff, as CISM now controls the fate of the snow mass.

- SMB is also computed for the natural vegetated land unit, which can only generate a zero or positive SMB. A positive SMB triggers glacial inception when running with an evolving ice sheet.