The visualization below shows the results of using the SCALGO Hydrology software on the entire SRTM (Shuttle Radar Topography Mission) CIAT-CSI dataset to assess the risk of flooding due to rising sea-level and the flooding vulnerability due to extreme rain. The SRTM dataset provides an (almost worldwide) 3 arc-seconds (90-meter at equator) resolution raster terrain dataset from 60° north to 56° south. The raster contains 62 billion cells of which about 17 billion contain real data. It is stored in 874 files (tiles) and takes up more than 200 gigabytes on disk.
The risk of flooding due to rising sea-level was assessed by computing for each cell the minimal sea-level rise that results in flooding of the cell (that is, the level—or flooding height—where the cell is connected to the ocean by cells below the level).
The flooding vulnerability due to extreme rain was assessed by first flooding the terrain, that is, removing (filling) all terrain depressions, and then computing a flow direction for each cell (that is, the direction water flows from the cell), and finally the flow accumulation for each cell (that is, the amount of water that reaches the cell if a unit of water is initially placed on each cell). The flow accumulation of a cell corresponds to the number of "upstream" cells (ie. an area) and can therefore be used to assess the risk of flooding due to extreme rain; river networks are often extracted as the cells with a flow accumulation value above a certain threshold.
All of the computation steps are quite standard, but SCALGO software can perform them on a massive dataset such as SRTM. Using the SCALGO Hydrology software the calculations were performed on the entire SRTM 60.6 billion cell raster dataset without thinning or tiling.
Visualization of Sea-Level Rise or Flow Accumulation can be selected on the right of the map. The watersheds defined by the flow directions can be shown as well (a watershed is a set of cells where water on the cells flow into the same depression).