Garden with Insight
Garden with Insight v1.0 Help: Soil patch next day functions: calculate today's soil temperature for each layer
To calculate the soil surface temperature, first the bare-soil surface temperature is calculated. Bare-soil
surface temperature is based on the solar radiation today (brighter =
hotter), the soil albedo (less reflection = hotter), the soil cover index (less soil cover = hotter), and whether today is a wet day (it
rained) or a dry day (dry day = hotter). Notice that the soil cover index is involved in calculating the
bare soil surface temperature, so calling this the bare-soil temperature is not really correct. It's
more like a first approximation of the soil surface temperature.
Soil with mulch or snow on it warms up and cools down more slowly
than bare soil. To simulate the insulating effect of vegetation cover and snow on the soil temperature, the
bare-soil surface temperature is combined with yesterday's soil temperature in the second soil layer using a lag factor. (The second
soil layer temperature is used instead of the first because the first soil layer is always only ten millimeters
thick.) The lag factor is based on two S curves: the effect of vegetation
cover, and the effect of snow. The coefficients for the vegetation cover S curve are parameters; the ones for the snow S curve are constants.
Now that we have the final soil surface temperature, all that remains is to calculate the temperature in
each soil layer. Because soil water is a good insulator, as you move down the soil profile changes in the soil temperature are dampened
(reduced). At a depth of two meters or so, soil temperature changes very little year-round, unless
the soil is very dry. A damping factor is calculated from soil water content and bulk density (which determines maximum soil water content). With this
damping factor the temperature at the center of each soil layer is calculated.
If the "update soil temperature" option is turned off, this calculation is not done and yesterday's
soil temperatures (at the surface and for each layer) are carried over to today.
calculation of albedo, soil cover
EPIC Soil Temperature