2.3.2 Xinanjiang Model
The Xinanjiang model, which is a conceptual rainfall–runoff model
developed by Zhao et al. (1980), has been widely used in many regions of
the world (Lin et al., 2014; Liu et al., 2009; Yao et al., 2014). In the
model, actual evapotranspiration is computed from potential
evapotranspiration while the soil storage deficit is represented in
three layers, i.e., upper, lower and deep soil layers. The total runoff
of the basin is divided into surface runoff, interflow and groundwater
runoff using a free water capacity distribution curve and is estimated
using a soil moisture storage capacity distribution curve based on the
concept of runoff formation on repletion of storage. The surface runoff
is routed by the lag–and–route method, while interflow and groundwater
are routed through linear reservoirs representing interflow and
groundwater storage, respectively (Zhao., 1992; Zhao and Liu., 1995).
The determination of the sensitive parameters was adopted to the results
of a local sensitivity analysis. We observed the change in the outputs
of discharge and runoff by disturbing all parameters. The sensitive
parameters in the Xinanjiang model mainly include the evapotranspiration
coefficient (K C), areal mean free water capacity
of the surface soil layer (SM ) and the recession constant of
surface water storage (CS ) (Table 2). KCcontrols the total water balance, which is important for water
calculations. SM plays a decisive role in the amount of surface
runoff, which reflects the ability of surface soil to store water and
determines the proportion of surface runoff and groundwater. CSreflects the geomorphology of the river network and determines the final
flow process. The ranges of parameters were chosen based on the work of
Ren et al. (1989), Wang & Zhao (1989) and Zhao et al. (1992). In this
research, 20 samples were generated following LHS method for these
uncertain parameters. We assumed that uncertain parameters follow
uniform or normal distributions.