Theory
Driving variables are variables that are the driving forces for water, heat, nitrogen and carbon fluxes in the CoupModel. These variables are for example meteorological data that varies over the period that is simulated. The model can be run in several simulation modes depending on the purpose of the simulation. Each mode has its own requirements for driving variables.
The most common simulation mode, thus far, has been to simulate, on an annual basis, both soil heat and water flows in a natural, vegetated soil. This mode requires the input of the following meteorological variables once a day: Precipitation, air temperature, relative humidity, wind speed, net radiation and global, shortwave radiation. Ideally, these variables should be measured at a reference height above vegetation, but being daily sums or averages, it will commonly be sufficient to use data from a nearby standard meteorological network station. If, by chance, a reliable measure of potential transpiration can be given, this measure will substitute relative humidity, wind speed and net radiation.
If, on the other hand, some of the driving variables are not measured, they can be substituted by analytical expressions or they can be deduced from other measurements. Global radiation can be substituted by degree of cloudiness or duration of bright sunshine. Relative humidity, wind speed and cloudiness could each be substituted by parameter values representing average conditions for longer time periods. Net radiation can be substituted by global radiation. The minimum requirement to produce realistic results from simulations of annual heat and water flows is to have only measured precipitation and air temperature.
Precipitation