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Table 1

Hydrologic parameters used in the indicators of hydrological alteration (IHA) and their grouping definition and abbreviation. Adapted from IHA Manual (Nilsson & Berggren 2000)

IHA statistics groupHydrologic parametersAbbreviated name
Group 1: Magnitude of monthly water conditions (12 indices) Mean value for January January 
Mean value for February February 
Mean value for March March 
Mean value for April April 
Mean value for May May 
Mean value for June June 
Mean value for July July 
Mean value for August August 
Mean value for September September 
Mean value for October October 
Mean value for October October 
Mean value for December December 
Group 2: Magnitude and duration of annual extreme water conditions (12 indices) Annual minima 1-day means 1-day min 
Annual minima 3-day means 3-day min 
Annual minima 7-day means 7-day min 
Annual minima 30-day means 30-day min 
Annual minima 90-day means 90-day min 
Annual maxima 1-day means 1-day max 
Annual maxima 3-day means 3-day max 
Annual maxima 7-day means 7-day max 
Annual maxima 30-day means 30-day max 
Annual maxima 90-day means 90-day max 
Base flow index Base flow 
Number of zero flow days Zero flow days 
Group 3: Timing of annual extreme water conditions (2 indices) Julian date of each annual,1-day maximum Date min 
Julian date of each annual,1-day minimum Date max 
Group 4: Frequency and duration of high and low pulses (4 indices) Number of low pulses within each water year Lo pulse # 
Mean or median duration of low pulses (days) Lo pulse L 
Number of high pulses within each water year Hi pulse # 
Mean or median duration of high pulses (days) Hi pulse L 
Group 5: Rate and frequency of water condition changes (3 indices) Rise rates: Mean or median of all positive differences between consecutive daily values Rise rate 
Rise rates: Mean or median of all negative differences between consecutive daily values Fall rate 
Number of hydrologic reversals Reversals 
IHA statistics groupHydrologic parametersAbbreviated name
Group 1: Magnitude of monthly water conditions (12 indices) Mean value for January January 
Mean value for February February 
Mean value for March March 
Mean value for April April 
Mean value for May May 
Mean value for June June 
Mean value for July July 
Mean value for August August 
Mean value for September September 
Mean value for October October 
Mean value for October October 
Mean value for December December 
Group 2: Magnitude and duration of annual extreme water conditions (12 indices) Annual minima 1-day means 1-day min 
Annual minima 3-day means 3-day min 
Annual minima 7-day means 7-day min 
Annual minima 30-day means 30-day min 
Annual minima 90-day means 90-day min 
Annual maxima 1-day means 1-day max 
Annual maxima 3-day means 3-day max 
Annual maxima 7-day means 7-day max 
Annual maxima 30-day means 30-day max 
Annual maxima 90-day means 90-day max 
Base flow index Base flow 
Number of zero flow days Zero flow days 
Group 3: Timing of annual extreme water conditions (2 indices) Julian date of each annual,1-day maximum Date min 
Julian date of each annual,1-day minimum Date max 
Group 4: Frequency and duration of high and low pulses (4 indices) Number of low pulses within each water year Lo pulse # 
Mean or median duration of low pulses (days) Lo pulse L 
Number of high pulses within each water year Hi pulse # 
Mean or median duration of high pulses (days) Hi pulse L 
Group 5: Rate and frequency of water condition changes (3 indices) Rise rates: Mean or median of all positive differences between consecutive daily values Rise rate 
Rise rates: Mean or median of all negative differences between consecutive daily values Fall rate 
Number of hydrologic reversals Reversals 
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