The historical flood analysis tool was build upon the Joint
Research Centre (JRC) Global Surface Water dataset. The JRC dataset
contains maps of the location and temporal distribution of surface
water from 1984 to 2015 and provides statistics on the extent and
change of those water surfaces. These data were generated using
3,066,102 scenes from Landsat 5, 7 and 8 acquired between 16 March
1984 and 10 October 2015. 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 The
Monthly History collection holds the entire history of water
detection on a month-by-month basis. The collection contains 380
images, one for each month between March 1984 and October 2015. 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.
The historical flood analysis tool presents the occurance of
surface water for the selected period. A 100% water occurance means
that all datapoints in the collection are identified of water
(permanent water), 50% implies a location that is inundated half of
the time. Locations with a low surface water occurance have only
been inundated for a short period in the whole period, likely caused
by flood events.
It is important to note that not all historical floods are
recorded in the dataseries. Floods might have occured between two
overpasses of the satellites or observations might have been
compromised by atmospheric conditions.
The tool helps to identify areas prone to flooding using the
complete Landsat archive. Areas which have been flooded in the past
are also prone to floods in the future.