Computation

The FastFlood method provides such an advance in compute time, that we can run the model on the user's hardware (client-side). The current version of the FastFlood model carries out all computations on the central processing unit of the user’s device, whether that is a phone, tablet, laptop, computer, or server. We facilitate this by running the model through WebAssembly technology, reaching near speeds of the C++ programming language compiled to native byte code. If you are reaching the limits of our web platform, please contact us for options in stand-alone executables.

Expect the following memory requirements and compute time for various grid sizes:

If you think this is a lot of compute, try running a traditional full flood simulation— for example using the LISEM model—and find it is about 1500× slower! Note that the model runs on your own device. There is no server doing calculations for you, which allows for this tool to be free. Having a stronger CPU and more memory can help with compute time. The compute time for the model depends on a couple factors:

For higher domain sizes, more compute is required. In addition to this linear increase with pixel count, the flow accumulation and hydro-correction schemes must carry out more iterations as well. The settings play a crucial role as well. The non-linear correction makes heavy use of power-law estimation on the CPU, which slows down the model by a factor of approximately 2. If you are having trouble with simulation time, try to lower the resolution of your simulation. It is typically pointless to simulate large regions at anything more than 10 meter resolution. Hybrid approaches (feeding a small detailed simulation with output from a regional simulation) are much more suited then.

Because the FastFlood model runs all calculations on the user's side, no data needs to be uploaded or downloaded. While it may seem like the browser is sending data to the fastflood.org website, in reality, the GeoTIFF files provided by the user are parsed and stored in user-machine memory. Thus, there is no reason to worry about data rights and confidentiality, as the FastFlood servers never see any of your data, processing steps, simulation details, or anything else. All that is known is the usage of the global datasets that are available for automatic download.