Overview

WindNinja is a computer program that computes spatially varying wind fields for wildland fire application. It requires elevation data for the modeling area (in the form of an ASCII Raster DEM file, FARSITE landscape file, GeoTiff, or ERDAS Imagine file), a domain-mean initial wind speed and direction, and specification of the dominant vegetation in the area. An optional diurnal slope flow model can be turned on, which requires additional inputs of date and time, lat/long of domain center, percent cloud cover, and air temperature. Outputs of the model are ASCII Raster grids of wind speed and direction (for use in spatial fire behavior models such as FARSITE and FlamMap), a GIS shapefile (for plotting wind vectors in GIS programs), and a .kmz file (for viewing in Google Earth). WindNinja is typically run on domain sizes up to 50 kilometers by 50 kilometers and at resolutions of around 100 meters.

WindNinja or WindWizard?

Users are often confused about which wind model they should use: WindNinja or WindWizard. Each of these models has certain advantages and disadvantages and the best choice will depend on the particular situation. Below is a list of advantages and disadvantages of each model to help make the right choice:

WindNinja

• Advantages
  • free
  • fast (8-45 seconds depending on hardware and simulation settings)
  • diurnal slope flow model
  • accounts for non-neutral atmospheric flows
    
    
• Disadvantages
  • less accurate during moderate to strong winds in the lee areas of hills/mountains where recirculation zones are likely to occur

WindWizard

• Advantages
  • more accurate during moderate to strong winds in the lee areas of hills/mountains where recirculation zones are likely to occur
    
    
• Disadvantages
  • no longer available
  • not free
  • slower (30 min to 2 hours per run)
  • no diurnal slope model
  • assumes flow is of neutral or near-neutral stability

In general, WindWizard will be more accurate for stronger winds (since diurnal slope flow effects are small, and WindWizard more accurately simulates momentum effects) and WindNinja will be more accurate for weaker winds (especially when diurnal slope flows significantly affect the wind patterns). If WindWizard is unusable for high winds (because of cost, licensing, or long simulation times), WindNinja can be used for all cases.