7-day Streamflow Forecasts


This glossary defines the key terms used on the 7-day Streamflow Forecasts portal.



The land area draining to a point of interest, such as a water storage or monitoring site on a watercourse.

catchment area

The extent of land where water from precipitation drains into the water storage.

deterministic forecast

A single valued forecast derived from a unique set of known input data and a forecast model.

ensemble forecast

A set of multiple forecasts for the same period and location. The spread of multiple forecasts provides information about forecast uncertainty.


The flow of water in streams, rivers and other channels.

Synonym: streamflow

mean absolute error

The average of absolute values of the difference between observed and simulated values for a set of simulated data.


The middle number of a given sequence of numbers. When the sequence contains an even amount of numbers, the median is the mean of the two middle values.

Source: The first part of definition sourced from Macquarie Dictionary Fifth Edition, 2009, Macquarie Dictionary Publishers.

numerical weather prediction (NWP)

A science focused on taking current observations of weather and processing these data with computer models to forecast the future state of weather.

Source: Modified from NOAA, viewed 25 July 2015.


One of a series of threshold values that divides a set of ordered data into 100 groups with an equal number of data points in each.

For example, consider a dataset of annual rainfall totals arranged in increasing order. The 20th percentile is a value with 20% of the data below it and 80% above it. The 90th percentile is a value with 90% of the data below it and 10% above it.


All forms in which water falls on the land surface and open water bodies as rain, sleet, snow, hail, or drizzle.

probabilistic forecast

A probabilistic streamflow forecast shows the range of possible streamflow volumes and how likely it is that they will occur.

skill score

A statistical score used to assess the relative performance (skill) of a model against a reference forecast (e.g. climatology).

Skill Score =(Smod - Sref) / (Sperf - Sref)


Smod = Score for the model forecast

Sref = Score for a reference forecast, e.g. climatology

Sperf = Score for a perfect forecast, usually 0 or 1

stream length

Longest distance along the stream from the point of consideration to the most distant headwater source.

Source: Modified from USGS, viewed 4 September 2015.


The flow of water in streams, rivers and other channels.

Synonym: flow


A state of lack of confidence to exactly describe the current or future condition of a system when limited knowledge of that system is available.

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