3.3 Parameter Estimation
The observed event-based runoff in the XDG watersheds were divided into
two groups by plots: the datasets of cropland and one grassland plot
were used for calibration and the remaining datasets of another
grassland plot were used for validation. All the parameters used in the
test methods were optimized using the Marquardt (1963) algorithm for
solving constrained least squares problems. In order to examine the
applicability of the models, λ=0.2 assigned in its original development
is adopted for the original SCS-CN, Huang et al.(2006), Huang et
al.(2007) and the proposed method (Method 1), and the slope parameters
(a1 and a2) obtained from Huang et
al.(2006) were also used for Huang et al. (2006) and the proposed method
(Method 1). Moreover, the effect of initial abstraction and slope on the
proposed method were tested with the optimized λ (Method 2) and both
optimized λ and slope parameters (Method 3).