Dynamic vegetation module

Usage of the dynamic vegetation module in SPHY requires the availability of a time series of NDVI maps of the study area. These are prepared in the same format and naming conventions as the meteorological forcing map series (ndvi0000.001, etc.). NDVI maps for SPHY applications are typically derived from satellite-based sensors such as Sentinel-2, Landsat 8, or MODIS. As these satellites do not have daily overpass frequencies and clouds sometimes hinder the acquisition of high-quality images, daily NDVI maps are unlikely to be available. When SPHY is run with daily time steps, the model takes the most recent NDVI image until a new one is available from the forcing map series.

The NDVI is used within SPHY as an important indicator of vegetation vigor and amount of vegetation. It allows for dynamic simulation of processes such as evapotranspiration, interception and canopy storage. To couple NDVI with Kc (see Eq. 3), it is required to set maximum and minimum NDVI values that are linked to max and min Kc. Although these can be introduced as constant values, when modeling heterogeneous areas it is recommended to provide the model with spatial maps of these constants varied by land use/land cover class. Similarly, (see Eq. 6) typically depends on vegetation type and should be listed in a lookup table. Table 14 shows the values for a certain number of vegetation types.

Table 13: Overview of mandatory inputs to the SPHY dynamic vegetation module

Parameter	Spatial map [SM], single value [SV]	For maps: Boolean [BO], Nominal [NO], Scalar [SC], Directional [DI]. For single value: Integer [IN] or Float [FL]	Unit
Kcmax	SM, SV	SC	[-]	Free	kcmax_utm.map
Kcmin	SM. SV	SC	[-]	Free	kcmin_utm.map
NDVImax	SM, SV	SC	[-]	Observable	ndvimax.map
NDVImin	SM, SV	SC	[-]	Observable	ndvimin.map
NDVI	SM	FL	[-]	Observable	forcing mapseries (ndvi0000.*)

Table 14: LAImax values for different vegetation types (Sellers et al., 1996)

Vegetation type	LAImax [-]
Broadleaf evergreen trees	7
Broadleaf deciduous trees	7
Mixed trees	7.5
Needleleaf evergreen trees	8
High latitude deciduous trees	8
Grass with 10 - 40% woody cover	5
Grass with <10% woody cover	5
Shrubs and bare soil	5
Moss and lichens	5
Bare	5
Cultivated	6