This table provides metadata for the actual indicator available from UK statistics closest to the corresponding global SDG indicator. Please note that even when the global SDG indicator is fully available from UK statistics, this table should be consulted for information on national methodology and other UK-specific metadata information.
Change in the extent of open and groundwater over time
Open water area - Open water area includes large lakes, rivers, estuaries and artificial waterbodies. The data presented for this series has been constrained to official high-water mark boundaries, which helps ensure that coastal water is not included in estimates. Measures therefore differ to those on the Freshwater Ecosystems Explorer, a Global Surface Water Explorer (GSWE) platform for presenting data specifically for this indicator. See Other Information for more details.
Nationally derived quantity of groundwater - Percentage change in groundwater level over time, of major groundwater aquifers. Data are provided by the British Geological Survey (BGS).
|Unit of measurement||
Percentage change (%) and Square kilometres (km²)
Extent - As used in the title of this indicator, 'extent' is expanded beyond spatial extent to capture additional basic parameters needed for the protection and restoration of water-related ecosystems. Extent includes three components - the spatial extent or surface area, the quality, and the quantity of water-related ecosystems.
Open water body area - Area of surface water unobstructed by aquatic vegetation. This includes the following 3 water-related ecosystem categories - rivers and estuaries, lakes, and artificial waterbodies.
Permanent water - Area that is under water throughout the year.
Seasonal water - Area that is under water for less than 12 months a year.
Ephemeral water - Area that is episodically under water in different years.
HydroBASINS - A series of polygon layers that depict watershed boundaries at a global scale. They use the Pfafstetter coding system, which allows for analysis of catchment topology. Catchments can be broken down into smaller sub-basins; with each subdivision, the Pfafstetter level increases. Here, a Pfafstetter level of 6 was used, giving us data for 38 catchments across the UK.
Open water area is broken down by water type - permanent, seasonal, and ephemeral.
Open water and Nationally derived groundwater level are both broken down by geography (HydroBASISNS). Each HydroBASISNS starts with a unique HydroBASINS code, which is followed with a description of where the basin is. This description is not an official part of the HydroBASINS name.
There are more data and disaggregation options available from the UNSDG database (official estimates by the UN using the GSWE) not reported here.
Open water area
Proportion of area = (spatial extent / land area) x 100
Percent change in spatial extent from baseline = ((average spatial extent of 5 year period - average spatial extent from 2001-2005) / average spatial extent from 2001-2005) x 100
Code for extracting data from the Global Surface Water Explorer and aggregating water to UK boundaries and HydroBasins can be found in the Data Science Campus GitHub.
Percent change in groundwater level = ((average ground water of 5 year period - average groundwater level from 1990-1994) / average spatial extent from 1990-1994) x 100
Average % change across hydrobasins = (sum of percent change in groundwater level from all groundwater stations)/ total number of ground water stations * 100
Open water area
The 'Open water area' series data is derived from the Global Surface Water Explorer (GSWE) but has undergone further refinement to ensure coastal water is not included in the estimate. Therefore, values differ to those on GSWE. Please see the blog Using satellite imagery to report changes to water bodies for SDG 6.6.1 for more information on this indicator.
Data for open water is derived from Earth Observation data (from the Landsat satellite programme). The resolution used does not pick up smaller waterbodies (including, small lakes, rivers and streams). These data can be downloaded from the Global Surface Water Explorer (GSWE).
The data presented here have been constrained to official high-water mark boundaries, which helps to ensure that coastal water is not included in estimate. Measures therefore differ to those on Freshwater Ecosystems Explorer, a GSWE platform for presenting data specifically for this indicator. The calculations for change from baseline (see 'Calculations' section above) are also slightly different from the ones described in the global UN metadata for the indicator.
Persistent cloud cover can impact the quality of data collection. Anomalous years (likely due to cloud cover - 1994 to 1998 and 2004 to 2009) have therefore been excluded from the data presented here, with the exception of the baseline. The baseline period of 2001 to 2005 includes the anomalous years 2004 and 2005. To mitigate the impact of variable cloud cover, the modal value of each pixel across the baseline years has been used to calculate the average spatial extent in the baseline period. Further details on the source data and mitigating the impacts of these anomalous periods is provided in the Data Science Campus Quality and Methodology document.
HydroBASIN catchments are identified with numbers, however we have added descriptive names to each catchment in the dropdown menu - these are not official names.
Groundwater level data is obtained from BGS WellMaster database, derived from 154 groundwater level monitoring stations to provide groundwater estimates for 19 of the 34 HydroBasins in the UK. HydroBasin catchments are identified with numbers, however descriptive name have been added to the dropdown menu, these are not official names.
The chosen five-year reference period for the analysis is 1990 to 1994. Values greater than 100% imply average groundwater levels have risen since the period 1990 to 1994, while values less than 100% imply falling levels. Please note that this baseline reference contains a period of draught for the UK
The data monitored by measuring authorities in each nation (Environment Agency, Scottish Environment Protection Agency, Natural Resources Wales, Department of Agriculture, Environment and Rural Affairs) are passed to BGS periodically. All chosen sites have the following - monitoring frequencies of greater than one observation a month, are monitoring boreholes where groundwater levels are not systematically affected by abstraction, and are representative of local and regional groundwater systems.
Raw data is quality assured by measuring authority and are expected to be accurate to less than +/- 0.01 metre for data collected since 1990. On receipt by BGS an additional check is made to ensure all values fall within expected hydrogeologicaly plausible ranges.
Please note, the headline figure for UK show average percentage change across hydrobasins for which values are available (not all hydrobasins are represented), not the % change across hydrobasins.
See Freshwater Ecosystems Explorer for further information and additional data available. Also, estimated values for UK SDG global reporting on lake water quality, reservoir, and wetlands surface area are available from the UNSDG database.
Data follows the UN specification for this indicator. This indicator has been identified in collaboration with topic experts.
|Data last updated||12 May 2023|
|Metadata last updated||12 May 2023|