Draft Simulations Now Match Detailed Terrain Roughness
Draft runs now use the same terrain roughness as Detailed runs.
What’s new
Draft simulations now read upstream terrain roughness the same way Detailed simulations do. In every wind direction that a Draft and a Detailed run share, ArchiWind now uses the same inlet roughness (z0), so your Draft is a faithful preview of your Detailed result.
Why it matters
ArchiWind takes the roughness for each wind direction from land-cover data in a 500 m sector upwind of your site. Until now, the width of that sector depended on how many directions were simulated: 45° for Draft (8 directions) and 22.5° for Detailed (16 directions). Where land cover changes quickly around a site, such as a forest edge or a village next to open fields, the two sectors could see very different terrain. Draft wind results could then differ from Detailed by up to about 19% in those directions. When both runs used the same roughness, Draft stayed within about 2% of Detailed in our tests.
How it works
Draft still simulates 8 wind directions. For each one, roughness is now taken from a 22.5° sector centred on that direction, exactly as in the Detailed run. All 8 Draft directions are also part of the 16 Detailed ones, so both runs now use identical roughness there.
For the Israeli standard (IS 5281)
Detailed simulations under IS 5281 use 12 wind directions, one every 30°. Draft now samples roughness over a 30° sector for each of its 8 directions, the same width as Detailed.
At 0°, 90°, 180° and 270° the two runs share the direction, so the sectors and the roughness aligned however at the moment the Draft simulation has a raidus of 450m vs 600m for the Detailed one. It can create a slight mismatch in the roughness values. At 45°, 135°, 225° and 315°, Detailed has no matching direction. The Draft sector there sits across two Detailed sectors, so small roughness differences can remain in those four directions.
Land cover around a site (ESA WorldCover 2021) and the upwind sectors used to set inlet roughness under IS 5281. Top: Draft, 8 directions. Bottom: Detailed, 12 directions. The north, east, south and west sectors are identical in both runs. Each diagonal Draft sector overlaps two Detailed sectors.
What this means for your existing projects
Draft simulations run before [RELEASE DATE] used the wider sector. If you compare an older Draft with a new Draft or Detailed run of the same site, a few directions may differ. Re-run the Draft to compare like with like. Detailed simulations are not affected.
Get started
Nothing to change: every new Draft simulation uses the updated roughness automatically. The PDF report lists the roughness used in each direction.