Scientific foundations

Streamflow varies in amount, timing, duration, frequency, and rate of change. These parts of a flow regime describe different aspects of how water moves through a river system over time. Ecological processes can depend on both the usual pattern of flow and departures from it.

hydropattern lets you express selected parts of a flow pattern as conditions and assess observations against them. A configured component is a software classification: it says whether the observations meet the conditions you specified. It is not, by itself, a measure of ecosystem health or proof of ecological benefit.

The terminology used on this site follows the project's glossary. For broader scientific background, see Poff et al. (1997) and Yarnell et al. (2020).

What a configured condition means

A characteristic describes one aspect of a component. For example, a magnitude characteristic can require flow to exceed a threshold; a duration characteristic can require a sequence of qualifying timesteps to last for an acceptable number of observations. Conditions and their combinations are chosen for the analysis question and reference data. The values in examples are illustrative software inputs, not universal ecological criteria.

Use timing for the part of the calendar year when a condition is evaluated; magnitude for the observed flow level; duration for the length of a consecutive qualifying run; frequency for qualifying timesteps in forward windows or water years in interannual windows; and rate of change for the ratio between flow values separated by a configured number of timesteps. These characteristics answer different questions and use different units.

See evaluation order and interpretation for how characteristic outcomes combine, and the characteristic reference for configuration and evaluation details.

Water-year labels

Water-year labels use the ending-year convention: with an October 1 boundary, October 1, 2020 belongs to water year 2021. Timeseries carries its configured boundary into scenario results. Direct Result callers can pass first_day_of_water_year to identify_water_years(); the method rejects missing or conflicting boundary metadata rather than assuming January 1.

Boundary day uses a normalized 365-day calendar. February 28 and February 29 share a seasonal day label, but both observations stay in the same water year; calendar timestamps, not duplicate normalized day labels, establish the year boundary. Daily completeness accepts a missing February 29, but not other missing daily observations.

Exposure is based on observed calendar intervals, not known/unknown outcome counts. Each daily water year has denominator 366 only when its recorded observations include February 29; otherwise denominator is 365, including partial years. Monthly exposure is the number of observed months divided by 12. Unsupported cadence or gaps prevent time-based exposure calculations.