where \(h_{c}\) is the canopy height for a given day (m), \(h_{c,max}\)is the plant‘s maximum canopy height (m), \(\text{yr}_{\text{cur}}\) is the age of the tress (years), and \(\text{yr}_{\text{fulldev}}\) is the number of years for the tree species to reach full development (years). Once plant growth reaches the maximum canopy height, \(h_{c}\) remains the same until the plant is killed. However, the kill operation of tree is not activated in the model, and forest height will maintain its maximum value when forest growth stops (Neitsch et al., 2005).
Forest information used to represent periodic forest growth (FG) condition are forest height and LAI. Canopy height data was collected from forest type maps of Korea Forest Service where provides overall forest information in South Korea. LAI was retrieved from the Land Processes Distributed Active Archive Center (LP DAAC) where supports monthly LAI (MOD15A2) measured at a 1,000 m spatial resolution. However, the retrieval has the limitation that LAI data starts from 2000. Therefore, LAI data from 1976 to 1999 were regressed using the relationship between canopy height and LAI. The regression applied power function which shows the must proper curve fitting of canopy height and LAI (Yongwei, Xinsheng, Fang & Jinyan, 2013). Collected forest data were averaged and divided into a 10-year interval which is coincident with the interval used for GA database.
The leaf area development curve (Figure 4. (a)) and canopy height development curve (Figure 4. (b)) are determined by six parameters, two known points on the optimal leaf area development curve (\(\text{fr}_{\text{LAI}}\), \(\text{fr}_{\text{PHU}})\), the maximum LAI (BLAI), the fraction of the growing season at which senescence becomes the dominant growth process (DLAI), the maximum canopy height (CHTMX), and the number of years for the tree species to reach full development (\(\text{yr}_{\text{fulldev}})\). Since averaged values were retrieved and applied to SWAT, leaf area and canopy height development curves were devised by fitting the six parameters to maintain the LAI and canopy height at their periodic averages while simulating the watershed hydrology (Figure 4).
[Insert Figure 4]