Water yield: Data product specifications

1. Overview

1.1 Title

Water Yield: Data Product Specification

1.2 Reference date

2024-09-19

1.3 Responsible party

Census of Environment

Environment Accounts and Statistics Division, Statistics Canada

150 Tunney's Pasture Driveway
Ottawa, Ontario
K1A 0T6

Email: statcan.environ-environ.statcan@statcan.gc.ca

1.4 Language

eng – English

fra – French

1.5 Terms and definitions

Drainage regions: are a variant of the Standard Drainage Area Classification (SDAC) 2003. This classification groups 974 sub-sub-drainage areas representing all land and interior freshwater bodies into 25 drainage regions.

Ecoprovinces: are the second level (under ecozones) of the Ecological Land Classification, a hierarchical classification of ecological areas in Canada. There are 15 ecozones at the top of the ecological land classification hierarchy, which are subdivided into 53 ecoprovinces. They cover the entire terrestrial extent of Canada.

HYDAT: is an Environment and Climate Change Canada – Water Survey Canada database that contains computed data for the stations where hydrometric data are collected. It contains information on streamflow, water level and sediments in Canada.

Hydrometric network: refers to Environment and Climate Change Canada – Water Survey Canada’s network of stations where data on surface water quantity is collected.

North line: a line that delineates the North from the South in Canada based on social, biotic, economic and climatic variables. In this document, it delineates the northern extent of the annual datasets.

Renewable freshwater: refers to the water that regularly replenishes our rivers, lakes and aquifers. Non-renewable freshwater describes water that is stored in deep aquifers, ice caps and glaciers that have a negligible rate of recharge on a human time scale. Some freshwater in the Great Lakes and other major water bodies can also be considered non-renewable since the renewal rates are very low.

Runoff: the portion of precipitation and melt from snowpack and glaciers that, by a variety of paths above and below the surface of the ground, reaches the stream channel. Once it enters a stream channel, runoff becomes streamflow.

Water yield: is an estimate of freshwater runoff into streams and rivers and provides information on Canada’s renewable freshwater. It is derived from data on the unregulated flow of water in rivers and streams in Canada. Although the water yield provides an estimate of renewable freshwater, it can include some water that is considered non-renewable (e.g., melt water from receding glaciers).

1.6 Abbreviations and acronyms

1.7 Informal description of the data product

This product contains gridded datasets of annual and 30-year average estimates of water yield. Tracking water yield—an estimate of renewable water supply derived from HYDAT streamflow data—provides information to help understand water resources available for human use and ecosystem needs. Annual datasets are available for the years 1971 to 2021 and cover southern Canada. Thirty-year averages are available for 1971-2000, 1981-2010, and 1991-2020. They cover the terrestrial and freshwater extent of Canada, except for the Arctic Archipelago.

This product supplements Statistics Canada’s tabular estimates by providing users with more spatial data for visualization and spatial analytical uses. These raster datasets provide information to help assess water availability across regions. This can support understanding and monitoring of the sustainability of water use practices for user defined geographies.

These datasets are released as part of a suite of products associated with the Census of Environment (CoE). The CoE organizes data about Canada’s natural environment based on the System of Environmental-Economic Accounting international statistical standard including the SEEA Central Framework and the SEEA Ecosystem Accounting that take a spatial approach to accounting for ecosystems and natural capital. Water yield is a variable that is relevant under the Water asset accounts of the SEEA Central Framework.

The datasets will be updated on an occasional basis.

2. Specification scope

In these specifications, only one scope is used.

2.1 Scope Identification

Main.

2.2 Level

Series.

2.3 Level name

Main scope of the water yield series.

2.4 Level description

Gridded datasets of water yield over terrestrial and freshwater areas of Canada.

2.5 Extent

2.5.1 Description

This product is a series of two-dimensional datasets (no elevation):

• The annual series covers the south of Canada from 1971 to 2021.
• The 30-year average series covers Canada’s terrestrial and freshwater extent, except for the Arctic Archipelago, for periods between 1971 and 2020.

2.5.2 Vertical extent

The water yield data are two-dimensional. There is no elevation (z) associated with the data.

2.5.3 Horizontal extent

For the annual water yield series, the horizontal extent covers the area of Canada south of the north line. The thirty-year average datasets cover Canada’s terrestrial and freshwater extent, except for the Arctic Archipelago.

Description for Map 1

The title of this map is “Arctic Archipelago and north line of Canada”. This map provides visual representation of the area of the Canadian Arctic Archipelago as well as the line separating the north from the south of Canada. The map has two components: the main map and a legend.

The main map shows the terrestrial and freshwater extent of Canada, with black lines delineating the boundaries of the provinces and territories.

The North line is symbolized by a dark red line crossing the country from the west coast in the north of British Columbia to the east coast on the northwestern part of Newfoundland Island. Cities are marked on the map with a black dot: Victoria, Vancouver, Edmonton, Calgary, Regina, Winnipeg, Toronto, Ottawa, Montreal, Quebec, Fredericton, Charlottetown, Halifax, and St. John's are south of the north line, and Whitehorse, Yellowknife, and Iqaluit are north of the north line.

The Arctic Archipelago is represented by a hatched gray and yellow area. It includes a group of islands in the Arctic surrounded by the Arctic Ocean to the west, the Labrador Sea to the northeast and the Hudson’s Bay to the southeast. Iqaluit is located at the southeastern end of the Arctic Archipelago.

Legend:

Data table for Map 1 Table summary
This table displays the results of . The information is grouped by Symbol (appearing as row headers), , calculated using (appearing as column headers).

Symbol	Description
Yellow shaded area	Canada’s terrestrial and freshwater extent
Grey and yellow hatched area	Arctic Archipelago
Dark red line	North line

2.5.4 Temporal extent

The temporal extent covers the entire year from January 01 to December 31 for the annual series.

For the 30-year average series, the temporal extent covers a thirty-year period from January 01 of the first year to December 31 of the thirtieth year. Values are expressed as an average for the thirty years covered.

For the northern part of Canada, the temporal extent is limited because of a lack of coverage in the hydrometric network during certain years:

2.5.4.1 Beginning date

Annual series: 1971-01-01

2.5.4.2 Ending date

Annual series: 2021-12-31

2.6 Coverage

The scope applies to all coverages.

3. Data product identification

4. Data content and structure

4.1 Description

This product is composed of two series of raster datasets that quantify renewable freshwater estimates over Canada’s terrestrial and freshwater extent. These series contain 51 annual files and 3 thirty-year average files. This enables users to choose the data for the time period they require for their analytical purposes.

4.2 Feature information

Not applicable.

4.3 Coverage information

4.3.1 Description

Technical description: The water yield rasters contain estimates of renewable freshwater expressed as a depth (mm) of water for each corresponding time period at a 10 km resolution. This product is a result of a modeling process designed to provide estimates at large scales such as those of the ecoprovinces and drainage regions of Canada.

Type of coverage content: modelResult.

4.3.2 Coverage type

Continuous quadrilateral grid coverage.

4.3.3 Specification

4.3.3.1 Domain extent

Refer to section 2.5 of this document.

4.3.3.2 Range type

Name: Water yield

Value data type: Float (0-10000)

4.3.3.3 Common point rule

Not applicable.

4.4 Reference to the specification scope

Main.

5. Reference systems

5.1 Spatial reference system

5.2 Linear reference system

Not applicable.

5.3 Temporal reference system

Gregorian calendar.

5.4 Reference to specification scope

Main.

6. Data quality

6.1 Completeness

Annual water yield estimates cover southern Canada at a 10 km resolution. Thirty-year average water yield data cover Canada’s terrestrial and freshwater extent at a 10 km resolution but exclude the Arctic Archipelago because of poor network coverage. Estimates in the north are only provided for the years when sufficient data were available.

6.1.1 Commission

Not applicable.

6.1.2 Omission

The annual series excludes the north of Canada, and some years are omitted for the north in the thirty-year averages. Results are included when data points are dense enough to support estimation and sufficient data are available for validation. Few northern results are included because northern networks are much sparser, with significantly fewer stations and available data. Estimates for the Arctic Archipelago are excluded for these reasons. For further details on spatial and temporal extent, see section 2.5 of this document.

6.2 Logical consistency

6.2.1 Conceptual Consistency

Although the water yield provides an estimate of renewable freshwater, it can include some water that is considered non-renewable (e.g., meltwater from receding glaciers). Unregulated flow was prioritized, and most stations were selected on this basis. However, to account for changes in the regulation status in HYDAT, for data after 2014, the Reference Hydrometric Basin Network (RHBN) of the Water Survey of Canada (WSC) was used to identify stations for inclusion. The RHBN is a set of stations with minimal human influence.

6.2.2 Domain consistency

Verification and validation procedures, including the definition of selection criteria for the input data, the identification and removal of outliers and the comparison with streamflow data, ensure that the range of values remain coherent.

6.2.3 Format consistency

The use of well-established commercial software to generate formats for dissemination supports proper format consistency.

6.2.4 Topological consistency

The annual and 30-year rasters were aligned to the CoE 10 km grid. The annual rasters were generated with the same method and cover the exact same extent. The same process was applied to the 30-year rasters.

6.3 Positional accuracy

Unknown. The water yield is modeled using an interpolation method. Water flows from each WSC hydrometric station are assigned to the drainage basin centroid. The accuracy of the data depends on the data sources: the HYDAT dataset and the hydrometric network basins polygons from the Prairie Farm Rehabilitation program (PFRA) and WSC which provide the drainage basin area and location for each hydrometric station.

6.4 Temporal accuracy

Unknown. Information on the accuracy of the time measurement can be found in the data source (HYDAT) metadata. Visit ECCC-WSC HYDAT database for further details.

There are limitations in the data for the north, which were included in the thirty-year average datasets. Any change for the north must be interpreted with caution because of differences in the number of years and stations included. These time series datasets are intended to provide an average water yield for their specified time periods. For further details on the time coverage, see section 2.5 of this document.

6.5 Thematic accuracy

Unknown. The water flows reported at WSC hydrometric stations in the HYDAT dataset are inputs to the water yield spatial interpolation model. The accuracy of the data depends on the density of the network and on the quality of the data sources (water flow and area of the stations’ drainage basin).

Mean standard error maps are produced using the ordinary kriging model that give some information on uncertainty. The uncertainty largely reflects network coverage and density issues within and unique to each of the different zones (models). Mean standard error maps can be provided upon request as there are too many to practically release at this time.

7. Data capture

7.1 Description

To estimate water yield, a database of natural streamflow observations was compiled from the WSC HYDAT database. Stations with natural flow were identified through the regulation status in HYDAT. For data after 2014, the Reference Hydrometric Basin Network (RHBN) of the Water Survey of Canada (WSC) was used to identify stations with minimal human influence. The monthly streamflow values were converted to a runoff depth using the drainage area of the stations, then interpolated using ordinary kriging to produce spatial estimates of water yield. The interpolation method was applied to areas of Canada (kriging zones) that reflect network weaknesses and areas of the country where estimates can be expected to be more homogenous at the national scale.

Description for Map 2

The title of this map is “Zones in the kriging model for the water yield”. This map provides visual representation of Canada divided in four different zones used for the kriging model. The map has two components: the main map and a legend.

The main map shows the terrestrial and freshwater extent of Canada, with black lines delineating the boundaries of the provinces and territories.

Canada is divided into four mutually exclusive zones: Zone 1 is illustrated by a blue shaded area and includes most of British Columbia and the portion of southern Alberta where the Rocky Mountains are located. Zone 2 is represented by a yellow shaded area and includes the southern part of the Prairies. Zone 3 is represented by a green shaded area and includes southern Ontario and Quebec, as well as the Atlantic provinces except Labrador. Zone 4 is the remaining area shown as an orange shaded area and covers the North of Canada.

Legend:

Data table for Map 2 Table summary
This table displays the results of . The information is grouped by Symbol (appearing as row headers), , calculated using (appearing as column headers).

Symbol	Description
Blue shaded area	Zone 1
Yellow shaded area	Zone 2
Green shaded area	Zone 3
Orange shaded area	Zone 4

Kriging results for the different zones were then combined to produce the final gridded product. The annual rasters integrate results from zones 1, 2 and 3 and the 30-year average rasters include results from all four zones. Results along the borders of each zone were blended to address differences between adjacent zones and improve spatial consistency.

Results were included where data points are dense enough to support estimation and sufficient data are available for validation. Fewer northern results were included because networks in the north are generally sparser, with fewer stations available.

7.2 Reference to the specification scope

Main.

8. Data maintenance

8.1 Description

The data series is updated on an occasional basis.

8.2 Reference to the specification scope

Main.

9. Portrayal

Not applicable.

10. Data product delivery

10.1 Delivery format information

GeoTIFF

10.1.1 Format name

GeoTIFF: Geographic Tagged Image File Format.

10.1.2 Version

GeoTIFF 6.0

10.1.3 Specification

GeoTIFF is a format extension for storing georeference and geocoding information in a TIFF 6.0 compliant raster file by tying a raster image to a known model space or map projection.

10.1.4 File structure

Not applicable.

10.1.5 Language

eng – English

10.1.6 Character Set

utf8

10.2 Delivery medium information for Static Files

10.2.1 Units of delivery

Each dataset from the time series is delivered by year or 30-year period following these naming conventions:

Annual water yield: wy_sc_YYYY.tif

Ex. Water yield data set for the year 2005 in southern Canada: wy_sc_2005.tif

Thirty-year average water yield: wy_30y_YYYY_YYYY.tif

Ex. Water yield dataset for the 30-year average between 1971 and 2000 for Canada: wy_30y_1971_2000.tif

10.2.2 Transfer size

The file size changes according to the year. On average, an annual file is about 1.2 MB and a thirty-year average file is about 1 MB.

10.2.3 Medium name

File transfer.

Open Government of Canada website

www.geo.ca

10.2.4 Other delivery information

Information regarding the use of the data is defined in the Statistics Canada Open Licence.

10.3 Reference to specification scope

Main.

11. Additional information

Statistics Canada also produces tabular estimates of water yield in cubic kilometres and cubic metres per square metre by drainage regions and ecoprovinces as part of the CoE. These estimates can differ from those obtained by using the annual water yield rasters to generate estimates because of smoothing done at model or zone boundaries to make a more spatially consistent raster dataset. Details on the method applied to generate tabular estimates on water yield can be found on the Physical asset accounts page from the Methodological Guide on the Canadian System of Environmental-Economic Accounting.

12. Metadata

Supplemental information on the method used to generate water yield estimates can be found in The Water Yield for Canada As a Thirty-year Average (1971 to 2000): Concepts, Methodology and Initial Results.

12.1 Reference to specification scope

Main.