2.2. Some key switches

There are many variables that act together to determine how a run of JULES is set up and these are covered in detail in The JULES namelist files. Additionally, configurations illustrate suitable combinations of options. Here we highlight a few key switches that select broad areas of science, particularly for the benefit of new users.

The phenology model for natural vegetation can be enabled using l_phenol which uses the leaf turnover rate to calculate a time-varying Leaf Area Index (LAI).

To simulate carbon stocks in natural vegetation, the TRIFFID dynamic vegetation model can be enabled via the switch l_triffid. When TRIFFID is on, competition between tiles is switched on with l_veg_compete and the effect of nitrogen on vegetation growth is enabled via l_nitrogen.

The crop model, which is simulates phenology and carbon stocks in crops, can be switched on by setting the number of crop tiles ncpft to a non-zero value.

The crop model and TRIFFID cannot currently be used together. To simulate agricultural areas within TRIFFID, a fraction of the gridbox can be reserved for agricultural Plant Functional Types (PFTs) (as defined by crop_io > 0). Agricultural PFT competition and a representation of harvest carbon can be switched on with l_trif_crop.

If neither the phenology model nor the crop model are used, LAI for each vegetation tile can be set to a constant (lai_io) or a time series or seasonal cycle can be prescribed (JULES_PRESCRIBED).

To simulate carbon and nitrogen stocks in the soil, the 4-pool model should be selected by setting soil_bgc_model = 2. This option adds prognostic soil pools and must be used with the TRIFFID vegetation model. If TRIFFID is not used, prescribed soil pools must be invoked via soil_bgc_model = 1. Layered soil pools are used if l_layeredc = .TRUE..

A multi-layer snow model can be selected using nsmax. Parametrisations of surface and subsurface runoff generation are controlled using l_top and l_pdm, while the routing of water in rivers uses l_rivers.