The European Commission Joint Research Centre 'Global Surface Water Datasets' contain maps of the location and temporal distribution of surface water from 1984 to 2020 and provides statistics on the extent and change of those water surfaces. For more information see the associated journal article:
High-resolution mapping of global surface water and its long-term changes (Nature, 2016) and the online
Data Users Guide. These data were generated using 4,453,989 scenes from Landsat 5, 7 and 8 acquired between 16 March 1984 and December 2020. Each pixel was individually classified into water / non-water using an expert system and the results were collated into a monthly history for the entire time period and two epochs (1984-1999, 2000-2020) for change detection. To view all the datasets in context see the
Global Surface Water Explorer.
Purpose
The Global Surface Water Occurrence shows where surface water occurred between 1984 and 2020 and provides information on overall water dynamics capturing both the intra and inter-annual variability and changes.
Description (from the journal article)
The frequency with which water was present on the surface from March 1984 to October 2020 was captured in a single product called surface water occurrence (SWO). To compute SWO, the water detections (WD) and valid observations (VO) from the same months are summed, that is, water detections and valid observations from March 1984 are added to water detections and valid observations from March 1985 and so on, such that SWOmonth = ∑WD month / ∑VO month Averaging the results of all monthly SWOmonth calculations gives the long-term overall surface water occurrence. The month-by-month time step normalizes occurrence against seasonal variation in the number of valid observations across the year. Typically, more cloud-free observations (and thus valid observations) are available during dry seasons than wet. Without monthly weighting, the overall water occurrence (that is, computed over the full period) would be biased by temporal distribution of the valid observations (that is, giving more weight to the dry season than to the wet season).
Related datasets
The Occurrence 2020 dataset is one of six water-related datasets produced by JRC/Google. The other datasets are also available in the public domain: