Spatial Modeling of Maximum Capacity Values of Irrecoverable Rainfall
Retention by Forests in a Small Watershed
Abstract
With hydrologic calculations being performed, the most important factor
in forming and estimating rainfall runoff is the actual amount of rain
precipitations flowing under the tree canopies of the taiga zone. This
is due to the fact that only a portion of rainfall reaching the soil
through the forest canopy takes part in river runoff formation. At
present, in the understanding of hydrological processes there is no
unanimity on methods of estimating rainfall retention by the canopies of
different tree species in various natural geographical zones. The
existing estimation methods rely on empirical observations of net and
gross rainfall rather than on the results of physical modeling of
moisture on leaf surfaces in droplet form. The disadvantage of the
methods existing in the world is that it is not possible to make a
spatial estimation of rainfall captured by canopies. The purpose of this
study is mapping of maximum rainfall interception capacity for a small
forest watershed. Rainfall is retained on a canopy in droplet form
(droplet size varies from 10.6 to 18.6 mg). Specific water retention
(mass per unit leaf surface area) is determined by the leaf (needle)
roughness. The overall droplet retention on canopies is determined by
leaf surface area and precipitation intensity. The maximum mass of
rainfall retention on the canopies of individual deciduous trees reaches
77 kg, (3.0-4.0 mm per canopy projection area) and that of coniferous
trees is from 24.8 to 58.0 kg (1.9 to 5.9 mm). Taking into account
rainfall losses for canopy interception makes it possible to reduce the
margin of error in calculations of maximum rainfall flood loss from 126
to 25%.