The RVA method is a set of methods based on the IHA hydrological index system proposed by Richter *et al.* (2003) and Guo *et al.* (2018). The indicators selected by IHA can describe the changes in the hydrological situation in detail in five aspects: magnitude, timing, frequency, duration, and rate of change. In this study, an ecologically significant flow indicator system was established, including five groups of 32 indicators (Table 1). The following are the specific calculations:

(4)

(5)

Table 1

IHA parameter group . | Parameter index . |
---|---|

Monthly median flow | Median data for monthly flow |

Annual extreme flow | Annual average 1, 3, 7, 30, 90 days minimum and maximum flow, base flow index^{a} |

Annual extreme flow occurrence time | The time of the largest and smallest daily pulses in the year |

Frequency and duration of high and low pulses | The median of yearly high and low pulse count^{b}and pulse duration |

Change rate and frequency of flow change | The mid-year value of increase (rate of increase) and decline (decline rate). The number of reversals^{c} for increase (rate of increase) and decline (decline rate) |

IHA parameter group . | Parameter index . |
---|---|

Monthly median flow | Median data for monthly flow |

Annual extreme flow | Annual average 1, 3, 7, 30, 90 days minimum and maximum flow, base flow index^{a} |

Annual extreme flow occurrence time | The time of the largest and smallest daily pulses in the year |

Frequency and duration of high and low pulses | The median of yearly high and low pulse count^{b}and pulse duration |

Change rate and frequency of flow change | The mid-year value of increase (rate of increase) and decline (decline rate). The number of reversals^{c} for increase (rate of increase) and decline (decline rate) |

^{a}Base flow Index: The ratio of the minimum annual flow of 7 consecutive days to the annual median value.

^{b}Low pulse is defined as the median of the day lower than 25% of the frequency before the disturbance, and high pulse is defined as the median of the day higher than 75% of the frequency before the disturbance.

^{c}The number of reversals refers to the number of times the daily flow changes from increasing to decreasing or decreasing to increasing.

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