A schematic diagram demonstrating the coupling of 3T-KRGM and the XAJ model is shown in Figure 3. To couple the 3T-KRGM (see Section 2 for details) into the XAJ model, the karst-dominated watershed is first subdivided into pervious and impervious areas. The pervious area is further separated into the karst and non-karst pervious areas, with a parameter denoting how much of the watershed is made up of karst pervious areas. The proposed 3T-KRGM is solely applied to the karst pervious areas, whereas the corresponding modules of the XAJ model are applied to the non-karst pervious areas and impervious areas. The 3T-KRGM shares the same inputs as the XAJ model, producing , , and as output. The corresponding modules of the XAJ model produce surface runoff on the non-karst pervious areas (), interflow on the non-karst pervious areas (), groundwater on the non-karst pervious areas (), and surface runoff on the impervious areas (). , , and formed the total surface runoff (). and formed the total interflow runoff (). and formed the total groundwater runoff (). , , and were routed to the watershed outlet and formed discharge *Q* by using the flow concentration module of the XAJ model. The XAJ models with and without 3T-KRGM are referred to as the improved XAJ model and the original XAJ model, respectively. The parameters of the improved XAJ model and original XAJ model are listed in Table 1.

Table 1

Parameter . | Signification . | Range . |
---|---|---|

The ratio of potential evapotranspiration to pan evaporation | [0.6,1.5] | |

Evapotranspiration coefficient of deep soil layer | [0.1,0.2] | |

Averaged tension water storage capacity of upper soil layer | [5,30] | |

Averaged tension water storage capacity of lower soil layer | [60,90] | |

Averaged tension water storage capacity of deep soil layer | [15,40] | |

The ratio of impervious watershed area | [0.01,0.2] | |

The exponent of the tension water storage capacity curve | [0.1,0.4] | |

Averaged soil layer free water storage capacity | [10,30] | |

The exponent of the free water storage capacity curve | [1,1.5] | |

Outflow coefficient of interflow from free water storage | [0.1,0.55] | |

Outflow coefficient of groundwater from free water storage | 0.7 − | |

Recession coefficient of interflow storage | [0.5,0.9] | |

Recession coefficient of groundwater storage | [0.95,0.998] | |

Recession coefficient of water storage in river network | [0.1,0.9] | |

Lag time | [1,10] | |

The ratio of karst pervious area | [0.1,0.9] | |

The capacity of the epikarst reservoir | [10,100] | |

The capacity of the soil reservoir | [10,80] | |

Saturation water storage capacity on the karst area curve exponent | [0.1,0.4] | |

Interflow coefficient on karst pervious areas | [0.01,0.8] | |

Threshold of the SEI | [0,10] |

Parameter . | Signification . | Range . |
---|---|---|

The ratio of potential evapotranspiration to pan evaporation | [0.6,1.5] | |

Evapotranspiration coefficient of deep soil layer | [0.1,0.2] | |

Averaged tension water storage capacity of upper soil layer | [5,30] | |

Averaged tension water storage capacity of lower soil layer | [60,90] | |

Averaged tension water storage capacity of deep soil layer | [15,40] | |

The ratio of impervious watershed area | [0.01,0.2] | |

The exponent of the tension water storage capacity curve | [0.1,0.4] | |

Averaged soil layer free water storage capacity | [10,30] | |

The exponent of the free water storage capacity curve | [1,1.5] | |

Outflow coefficient of interflow from free water storage | [0.1,0.55] | |

Outflow coefficient of groundwater from free water storage | 0.7 − | |

Recession coefficient of interflow storage | [0.5,0.9] | |

Recession coefficient of groundwater storage | [0.95,0.998] | |

Recession coefficient of water storage in river network | [0.1,0.9] | |

Lag time | [1,10] | |

The ratio of karst pervious area | [0.1,0.9] | |

The capacity of the epikarst reservoir | [10,100] | |

The capacity of the soil reservoir | [10,80] | |

Saturation water storage capacity on the karst area curve exponent | [0.1,0.4] | |

Interflow coefficient on karst pervious areas | [0.01,0.8] | |

Threshold of the SEI | [0,10] |

Figure 3

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