GOTILWA: An Integrated Model of Water Dynamics and Forest Growth
165
A second set of input data is related to the functions used to describe the
hydrological fluxes through the canopy (throughfall, stemflow and interception) and through the soil (drainage). For each daily event of rainfall GOTILWA estimates the canopy fluxes as functions of the amount of rainfall and
the leaf area of each tree size class. The drainage is calculated by Darcy's law,
from topographic and soil parameters.
The third set of data is formed by the variables used to define the structure and function of the trees. Mean diameter (D) is the basic parameter
used to characterize the tree size. Initial aboveground biomass of a tree is estimated using the allometric relationship:
where Bi is the aboveground biomass of tree i, the diameter of which is Db
and a and b are empirical constants.
The biomass of each fraction at any given time is the result of the balance
between carbon fixation and respiration. The amount of water transpired
during a period of time determines the fraction of active xylem (sapwood)
and, thus, the leaf area of the tree. Since the ratio leaf area/sapwood area
should remain constant, any change in water availability results in changes in
the LAI and changes in the sapwood/heartwood ratio.
12.1.2 Temporal Resolution
Interception, throughfall and stemflow are calculated daily from the amount
of rainfall data and the forest structure (density and size of the trees). The
soil water content is used to estimate both daily streamflow and actual
evapotranspiration. The daily Ea is integrated on a monthly basis and then
the subsequent physiological processes of trees, namely carbon uptake, respiration, carbon allocation, litterfall, and growth, are estimated on this monthly
basis.
12.1.3 Spatial Resolution
Two different spatial approaches can be used. In one of them, GOTILWA
works at the stand level integrating the values of the output variables on a
hectare area basis. In the second one, GOTILWA analyzes a catchment as a
unit integrating the differences in forest structure, and the main topographical and pedological features. In this case a classification of the whole catchment in categories as stands of uniform characteristics should be provided.
GOTILWA can subsequently analyze each of these uniform categories and
integrate the results to provide the output at the catchment level.
165
A second set of input data is related to the functions used to describe the
hydrological fluxes through the canopy (throughfall, stemflow and interception) and through the soil (drainage). For each daily event of rainfall GOTILWA estimates the canopy fluxes as functions of the amount of rainfall and
the leaf area of each tree size class. The drainage is calculated by Darcy's law,
from topographic and soil parameters.
The third set of data is formed by the variables used to define the structure and function of the trees. Mean diameter (D) is the basic parameter
used to characterize the tree size. Initial aboveground biomass of a tree is estimated using the allometric relationship:
where Bi is the aboveground biomass of tree i, the diameter of which is Db
and a and b are empirical constants.
The biomass of each fraction at any given time is the result of the balance
between carbon fixation and respiration. The amount of water transpired
during a period of time determines the fraction of active xylem (sapwood)
and, thus, the leaf area of the tree. Since the ratio leaf area/sapwood area
should remain constant, any change in water availability results in changes in
the LAI and changes in the sapwood/heartwood ratio.
12.1.2 Temporal Resolution
Interception, throughfall and stemflow are calculated daily from the amount
of rainfall data and the forest structure (density and size of the trees). The
soil water content is used to estimate both daily streamflow and actual
evapotranspiration. The daily Ea is integrated on a monthly basis and then
the subsequent physiological processes of trees, namely carbon uptake, respiration, carbon allocation, litterfall, and growth, are estimated on this monthly
basis.
12.1.3 Spatial Resolution
Two different spatial approaches can be used. In one of them, GOTILWA
works at the stand level integrating the values of the output variables on a
hectare area basis. In the second one, GOTILWA analyzes a catchment as a
unit integrating the differences in forest structure, and the main topographical and pedological features. In this case a classification of the whole catchment in categories as stands of uniform characteristics should be provided.
GOTILWA can subsequently analyze each of these uniform categories and
integrate the results to provide the output at the catchment level.