A Method for Assessing Hydrological Alteration within Ecosystems (Richter et al. 1996)

Foundational scientific paper introducing the Indicators of Hydrological Alteration (IHA) methodology. Presents 32 hydrological parameters (later expanded to 33) organised in 5 groups that characterise ecologically relevant aspects of the flow regime: (1) magnitude of monthly water conditions, (2) magnitude and duration of annual extremes, (3) timing of annual extreme conditions, (4) frequency and duration of high and low pulses, and (5) rate and frequency of water condition changes. Establishes the scientific framework for quantifying how human activities — particularly dam construction, water abstraction, and land use change — alter the natural flow regime. Published in Conservation Biology 10(4): 1163-1174. This paper, along with its companion (Richter et al. 1997), forms the basis of the most widely used approach for assessing hydrological alteration globally.