Albedo of plant, soil and snow

The albedo value will be calculated as a function of the albedo for vegetation, the albedo for bare soil and the albedo for snow as:

         (4.109)

where f_bare is the fraction of snow free ground (see Eq. (4.64)),  f_canopy is the fraction of the radiation which is absorbed by the vegetation (see Eq. (4.70)-(4.71)). The vegetation albedo a_veg is given as parameter values similar to other vegetation characteristics (see chapter “Plant water processes”).

If an implicit plant is simulated the equation above has to be slightly modified:

                                     (4.110)

where a_vegsoil is the albedo for both the vegetation and the soil given as a parameter.

An empirical correction of a_veg is introduced during conditions of precipitation or interception at air temperatures below 0°C, to represent the influence of snow interception on the albedo of the vegetation:

                           (4.111)

where c_snowint is an adjustable parameter, which can take values between 0 and 1.

The albedo of the soil surface a_soil is calculated as:

                                  (4.112)

where k_a is parameter as well as the albedo for a dry, a_dry, and wet soil, a_wet, respectively. The soil water tension of the uppermost layer, ψ₁, is allowed to vary from 10¹ to 10⁷ cm. See viewing function Bare Soil Albedo Function.

Snow albedo is calculated as a function of snow surface age, S_age, and the sum of daily mean temperatures, ∑T_a, since the last snow fall in accordance with the ideas of Plüss (1997):

                                            (4.113)

where a_min, a₁, a₂ and a₃ are parameters. The short-wave radiation not reflected at the surface is assumed to be absorbed at the surface. See viewing function Snow Albedo Function.