Australian Water Information Dictionary

Water forecasts: Seasonal streamflow

25% quartile

The 25% quartile of a set of numbers is the value in which 25% of the numbers are below it and 75% of the numbers are above it when the numbers are arranged in ascending (increasing) order.

Synonym: first quartile

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75% quartile

The 75% quartile of a set of numbers is the value in which 75% of the numbers are below it and 25% of the numbers are above it when the numbers are arranged in ascending (increasing) order.

Synonym: third quartile

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Australian Hydrological Geospatial Fabric

The Australian Hydrological Geospatial Fabric (Geofabric) is a specialised Geographic Information System (GIS). It identifies and registers the spatial relationships between important hydrological features such as watercourses, water bodies, canals, aquifers, monitoring points and catchments.

Source: Geofabric website

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Australian Water Resources Council

Established in 1962, the Australian Water Resources Council (AWRC) was set up by the Commonwealth and Sate Governments as a non-statutory body. The council existed into the 1980s.

Source: National Library of Australia

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AWRC

Australian Water Resources Council

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Bayesian joint probability (BJP)

A statistical modelling method to produce predictions of seasonal streamflows. Application of the BJP method to streamflow forecasting was developed by the CSIRO.

See the Seasonal Streamflow Forecast Research papers section for more information.

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catchment

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

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continuous ranked probability score (CRPS)

A measure of forecast accuracy score calculated in the original measurement space. Both the forecast and the observation are converted to cumulative density functions. In the case of the observation, this is a step function. The squared area between the two functions is the single CRPS value, which is averaged across all forecasts. Alt text

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CSIRO

Commonwealth Scientific and Industrial Research Organisation

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drainage division

Representation of the catchments of major surface water drainage systems, generally comprising a number of river basins. In Australia, 12 drainage divisions were first defined in the 1960s by the Australian Water Resources Council. Australian drainage division boundaries were revised by the Bureau in 2010 in line with the creation of the Australian Hydrological Geospatial Fabric (Geofabric) based on the 9 second Digital Elevation Model.

Related: Bureau

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El Niño

Refers to the extensive warming of the central and eastern Pacific Ocean that leads to a major shift in weather patterns across the Pacific. In Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions. See the Climate Glossary webpage on El Niño for more information.

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El Niño Southern Oscillation

The oscillation between the El Niño climate phase and the La Niña phase, usually over several years. See the Australian Climate Influence webpage on ENSO for more information.

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ensemble forecast

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

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ENSO

El Niño Southern Oscillation

The oscillation between the El Niño climate phase and the La Niña climate phase, or opposite phase, usually over several years. See the Weather and Climate page on ENSO for more information.

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exceedance probability

The forecast probability that a particular variable such as streamflow volume will be exceeded.

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first quartile

The first quartile of a set of numbers is the value in which 25% of the numbers are below it and 75% of the numbers are above it when the numbers are arranged in ascending (increasing) order.

Synonym: 25% quartile

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flow

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

Synonym: streamflow

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Geofabric

The common abbreviation for the Australian Hydrological Geospatial Fabric.

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hindcast

A retrospective forecast using observed information to validate or test a mathematical model. Observed inputs for past events are entered into the model to see how well the output matches the observed streamflow volumes.

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historical reference or historical probability distribution

A probability distribution created by sampling the historical streamflow data record. It is the reference forecast used when skill scores are calculated from hindcast modelling results.

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Indian Ocean Dipole

A major contributor to rainfall variability over Australia. When the dipole is in a positive phase, the sea-surface temperature (SST) around Indonesia is cooler than average while those in the western Indian Ocean are warmer than average. The positive phase increases easterly winds across the Indian Ocean, while convection in areas near Australia reduces. This results in suppressed rainfall over the Australian region. During a negative phase, warmer than average SST near Indonesia and cooler than average SST in the western Indian Ocean, result in more westerly winds across the Indian Ocean, greater convection near Australia and enhanced rainfall in the Australian region. See the Weather and Climate page on Indian Ocean for more information.

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inflowing watercourses

The rivers and streams that flow into a water storage. If a water storage is not located on a watercourse it is referred to as being off stream.

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interquartile range (IQR)

A measure of statistical dispersion, being equal to the difference between the third and first quartiles. Also called the midspread or middle 50.

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IOD

Indian Ocean Dipole

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La Niña

The extensive cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with an increased probability of wetter conditions. See the Climate Glossary webpage on La Niña for more information.

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monsoon

The northern Australian monsoon season generally lasts from December to March. It is associated with the inflow of moist west to northwesterly winds into the monsoon trough, producing convective cloud and heavy rainfall over northern Australia. These moisture-laden winds originate from the Indian Ocean and southern Asian waters. The northern Australian wet season encompasses the monsoon months but can extend several months either side. See the Weather and Climate page on the Australian monsoon for more information.

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percentile

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.

Related: quantile

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pie chart

A circular chart that is divided into sectors. A pie chart is used to display tercile forecasts with three sectors representing low flow, near median flow and high flow.

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probabilistic forecast

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

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quantile

Denotes one of a series of threshold values that divides a set of ordered data into groups with an equal number of data points in each. The terms tercile, quartile, quintile, decile and percentile refer to quantiles that divide the distribution of data into 3, 4, 5, 10 and 100 equal parts, respectively.

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river region

Produced as part of the Australian Hydrological Geospatial Fabric (Geofabric). These regions align with, and are nested within, the revised drainage divisions.

Source: Geofabric Product Guide V2.0

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RMSE

root mean squared error

The square root of the average square error (SE) for a set of forecasts

The SE is the squared difference between the observed value and median of the forecast.

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RMSEP

root mean squared error in probability

The square root of the average square error in probability (SEP) for a set of forecasts

The SEP is the squared difference between the historical probabilities of the observed value and median of the forecast.

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root mean squared error

The square root of the average square error (SE) for a set of forecasts

The SE is the squared difference between the observed value and median of the forecast.

Synonym: RMSE

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root mean squared error in probability

The square root of the average square error in probability (SEP) for a set of forecasts

The SEP is the squared difference between the historical probabilities of the observed value and median of the forecast.

Related: root mean squared error

Synonym: RMSEP

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Seasonal Streamflow Forecast

A forecast of total streamflow volumes predicted at a particular gauging station, or for the total of inflowing watercourses into a water storage. The forecast can be for a specific period, ranging from one to several months.

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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)

Where

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

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SOI

Southern Oscillation Index

An index calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. See the Climate page on SOI for more information.

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Southern Oscillation Index

An index calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. See the Climate page on SOI for more information.

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storage

A pond, lake or basin, whether natural or artificial, for the storage, regulation and control of water.

Synonym: water storage

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streamflow

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

Synonym: flow

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tercile

A set of data arranged in order with values that partition the data into three groups, each containing one-third of the total data. To define these terciles, the historical data is arranged in order from lowest to highest and then the data is partitioned into three equal groups. The lowest third of the data values are defined as the lowest tercile, the middle third of the values are the middle tercile and the upper third of the values are the upper tercile. A tercile is a specific form of quantile.

For example, if you had 100 data values, the lowest tercile would contain the 1st–33rd data values, the middle tercile the 34th–67th values and the upper tercile the 68th–100th values.

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third quartile

The third quartile of a set of numbers is the value in which 75% of the numbers are below it and 25% of the numbers are above it when the numbers are arranged in ascending (increasing) order.

Synonym: 75% quartile

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water storage

A hydrological feature in which water is stored. Surface water storages include natural and artificial ponds, lakes, reservoirs and lagoons, also the bodies of water held behind weirs and dams.

In the National Water Account, surface water storages include only artificial or natural water storages connected to rivers, which primary purposes are medium to long term water storage to service surface water access rights. These storages can be managed by an organisation to provide water to an urban water system.

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watercourse

A river, creek or other natural watercourse (whether modified or not) in which water is contained or flows (whether permanently or from time to time); and includes:

(i) a dam or reservoir that collects water flowing in a watercourse;

(ii) a lake or wetland through which water flows;

(iii) a channel into which the water of a watercourse has been diverted;

(iv) part of a watercourse; and

(v) an estuary through which water flows.

Source: Based on content from the Federal Register of Legislation (https://www.legislation.gov.au/Details/C2018C00505), at 8 Febraury 2019. For the latest information on Australian Government law please go to Federal Register of Legislation

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Australian Water Information Dictionary

Water forecasts: Seasonal streamflow

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