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The model used in this paper is a conceptual rainfall-runoff model IHACRES (Jakeman & Hornberger 1993). This model has been widely applied to a variety of catchments for climate impact studies (Jakeman et al. 1993; Littlewood 1999; Letcher et al. 2001; Kim & Lee 2014). The model is composed of a non-linear module and a linear module as shown in Figure 4 and model parameters are listed in Table 1. A non-linear module converts rainfall to effective rainfall which is calculated from the following equations.
formula
1
where rk is the observed rainfall, C is the mass balance, l is the soil moisture index threshold and p is the power on soil moisture respectively. The soil moisture is calculated from:
formula
2
where is the drying rate given by:
formula
3
where is the drying rate at reference temperature, f is the temperature modulation, is the reference temperature, and is the observed temperature. A linear module assumes that there is a linear relationship between the effective rainfall and flow. Two components in this module, quick flow and slow flow, can be connected in parallel or in series. In this study two parallel storages in the linear module is used and the streamflow at time step k is defined by the following equations:
formula
4
formula
5
formula
6
where and are quick flow and slow flow respectively and and β are recession rate and peak response respectively. The relative volumes of quick flow and slow flow can be calculated from:
formula
7
Table 1

Parameters in the IHACRES model

ModuleParameterDescription
Non-linear c Mass balance 
τw Reference drying rate 
f Temperature modulation of drying rate 
Linear αq, αs, Quick and slow flow recession rate 
βq, βs Fractions of effective rainfall for peak response 
τs Slow flow recession time constant, τs = −Δ/ln(−αs
τq Quick flow recession time constant, τq = −Δ/ln(−αq
ModuleParameterDescription
Non-linear c Mass balance 
τw Reference drying rate 
f Temperature modulation of drying rate 
Linear αq, αs, Quick and slow flow recession rate 
βq, βs Fractions of effective rainfall for peak response 
τs Slow flow recession time constant, τs = −Δ/ln(−αs
τq Quick flow recession time constant, τq = −Δ/ln(−αq
Figure 4

Structure of the IHACRES model.

Figure 4

Structure of the IHACRES model.

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