The amount of water residing on canopy is determined
by the precipitation interception and unloading
of the canopy. The former depends on the precipitation
amount and the canopy gap probability. The latter depends
on the vegetation and environmental conditions
such as wind speed. Their calculations are described in
Wang et al. (2007). Dew/frost formation on the canopy
is simulated in the model when the canopy temperature
drops below the dewpoint temperature of the air, which
(Wang et al. 2002a). However, when Ci is set to dynamic,
Eqs. (1) and (2) cannot be directly solved because
photosynthesis cannot be predetermined. In this
case, Eqs. (1) and (2) can be further coupled with the
following equation governing leaf CO2 balance