This module computes the pure runoff from each cell or group of cells or a hydrological discharge (see Runoff). It is also possible to perform hydrological modeling with the PREVAH system forced with the runoff grids produced by Alpine3D (see PREVAH hydrological modeling).

Runoff grid

In order to use the Alpine3D generated runoff as input for a hydrological model, it is often necessary to write out the generated runoff at each cell and timesteps. This is done by setting the WRITE_RUNOFF_GRIDS key to true in the [Output] section. The grids will be in the ARC ascii format by default but this can be configured with the RUNOFF_GRID2D key. The path where to write the grids must be provided thanks to the RUNOFF_GRID2DPATH key. For example, to write per-pixel generated runoff grids in the ARC ascii format:

[Output]
WRITE_RUNOFF_GRIDS = true
RUNOFF_GRID2D = ARC
RUNOFF_GRID2DPATH = ../output/runoff

Sub-catchments runoff sums

In order to work with multiple catchments, it is possible to write out the sum of all the runoff generated within a given sub-catchment. The sub-catchments must be properly defined before as shown in the sub-catchments inputs section. Then these sums will be written out in a SMET file that contains both the total runoff (from the bottom of the snow/soil column) as well as the precipitation, snow melt and glacier melt components (these ones at the bottom of the snow column only, ie from the surface runoff). Please note that the total runoff is at the bottom of the snow/soil column while the splitting (precipitation, snowmelt and glacier melt) are at the snow/soil interface (ie surface runoff), therefore the sum of the components is smaller than the total runoff (ie some of the runoff could not be classified).

In order to write the runoff sums at each time step, it is necessary to define the following keys:

CATCHMENT, in the [Input] section that gives the path and filename of the catchment definition grid;
CATCHMENTS_PATH, in the [Ouput] section that gives the path where to write the sub-catchments sums (one SMET file per sub-catchment)
CATCHMENT_NUMBERING (optional), in the [Input] section, which specifies which numbering scheme is used by the catchment definition grid to identify the individual sub-catchments. Two values are possible for this key: ALPINE3D_OLD (if the catchments are numbered with series of powers of 2, as described in the sub-catchments inputs section), or TAUDEM (if the catchments are identified with unique numbers, which are not required to be continuous)

On top of the runoff components, additional variables can optionally be averaged over each sub-catchment area and written in the output files at each time step. These variables must be specified using key RUNOFF_FILES_EXTRA_DATA, which accepts the standard meteorological variables (TA, RH, VW, ILWR, etc.) along with T_SOIL, which corresponds to the soil temperature at a certain depth. In case T_SOIL is present, the depths (in meters) at which soil temperature should be returned must be specified using key SOIL_TEMPERATURE_DEPTHS:

[Output]
RUNOFF_FILES_EXTRA_DATA = TA RH ISWR T_SOIL
SOIL_TEMPERATURE_DEPTHS  = 5 7.5 ; meters