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TitleDynamic surface water maps of Canada from 1984 to 2019 Landsat satellite imagery
AuthorOlthof, I; Rainville, T
SourceRemote Sensing of Environment 279, 113121, 2022., Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20210357
Mediapaper; digital; on-line
File formatpdf
Subjectsgeophysics; floods; flood potential; mapping techniques; satellite imagery; hydrography; flood plains; Climate change
ProgramCanada Centre for Remote Sensing (CCRS) Canada Centre for Remote Sensing
Released2022 09 15
AbstractKnowledge of the location of surface water in time and space is critical to inform policy on the environment, wildlife and human welfare. Dynamic surface water maps have been created at continental to global scales from medium and coarse resolution satellite image archives, most notably by Pekel et al. (2016), who mapped global water dynamics from 1984-2015 Landsat data. Their occurrence layer, depicting the percentage of time that water was observed in each 30m resolution cell, has been relied upon heavily by Natural Resources Canada's Emergency Geomatics Service (EGS) to map surface water during flood events. To generate dynamic surface water maps that are optimized for Canada's unique geography, the fully automated EGS surface water mapping methodology was applied in a cloud environment to the 1984-2019 Landsat archive over Canada. National-scale surface water maps and derived inundation frequency akin to Pekel's occurrence, as well as inter-annual wetting and drying trends calculated using per-pixel logistic regression, were produced to form the complete dataset. Separate comparisons of our frequency layer with Pekel's occurrence layer and Canada's water base layer from the National Hydrographic Network (NHN) were conducted. The comparison with Pekel's occurrence showed that our product contains a large number of unique water objects, the majority of which are correct when assessed against Google Earth (GE) imagery. Comparison with the NHN indicated that the NHN contained a large number of permanent water objects that were mapped as ephemeral objects in our product, with the majority of these being verified in GE as true ephemeral objects such as floodplains and wetlands. Wetting trends were found to be five times greater than drying trends across Canada, with notable wetting in the Prairie Pothole region and low-arctic verified with examples of statistically significant wetting and drying features. The dataset will enhance EGS flood and river ice mapping operations, provide information on floodplain location and extent, and give insight into the effects of climate change on surface water availability.
Summary(Plain Language Summary, not published)
This study created new detailed surface water maps of Canada showing where surface water has occurred, how often it has been observed at these locations and how it has changed between 1984-2019. We used archived, freely-available satellite imagery from the Landsat series of satellites to map water at bi-weekly and annual time periods, and use this series of water maps to generate dynamic surface water maps of Canada at national scale. These maps reveal the location of water, it's persistence in terms of percentage frequency from no water (0% frequency) representing land, to ephemeral or temporary water (>0% and <100% frequency) representing floodplains and wetlands, to permanent water (100% frequency) representing permanent lakes and rivers. These maps will be used to enhance flood hazard mapping by helping locate floodplains and wetlands across Canada, particularly where better information is unavailable for example in remote locations. Under cumulative effects, these maps will help inform development decisions by identifying sensitive riparian areas to avoid. They will also assist the Emergency Geomatics Services map floods in near real-time during emergency activations. In addition, we've mapped changes indicating locations that have become wetter or drier through time. This map shows areas where flooding has become more frequent, and will be used in partnership with Environment and Climate Change Canada as an indicator of surface water availability under a changing climate. It is also expected that a host of other applications, including enhancing land cover mapping, will emerge once the data become publicly available.

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