Wind multipliers are factors that transform regional wind speeds to local wind speeds considering local effects of direction, terrain, shielding and topographic influences. In order to assess the local wind hazard (spatial significance in the order 10's of metres), wind multipliers need to be computed, so that the regional wind speeds (order 10 to 100's of kilometres) can be factored to provide local wind speeds. These local wind speeds are critical to the wind-related activities including hazard and risk assessment. Activities also include agricultural growth and moisture demand applications along with energy-related applications such as wind farm developments. This document describes background information relating to wind multipliers and focuses on the development of a wind multiplier computation methodology. The Appendix provides an examples of the wind multiplier computation methodology to wind hazard and wind risk assessment.

Please note: The data can be downloaded for free in parts. Wind multipliers are factors that transform regional wind speeds to local wind speeds considering local effects of direction, terrain, shielding and topographic influences. In order to assess the local wind hazard (spatial significance in the order 10's of metres), wind multipliers need to be computed, so that the regional wind speeds (order 10 to 100's of kilometres) can be factored to provide local wind speeds. This data package includes terrain, shielding and topographic multipliers for national coverage. It is based on tiles with dimension about 1 by 1 decimal degree in netCDF format. Each multiplier further contains 8 directions. The version 2 dataset was produced using the wind multiplier computation software 2.0. See Geocat 82481.

Wind multipliers are factors that transform wind speeds over open, flat terrain (regional wind speeds) to local wind speeds that consider the effects of direction, terrain (surface roughness), shielding (buildings and structures) and topography (hills and ridges). During the assessment of local wind hazards (spatial significance in the order 10's of metres), wind multipliers allow for regional wind speeds (order 10 to 100's of kilometres) to be factored to provide local wind speeds. <b>Value: </b>The wind multiplier data is used in modelling the impacts (i.e. physical damage) of wind-related events such as tropical cyclones (an input for Tropical Cyclone Risk assessment), thunderstorms and other windstorms. <b>Scope: </b>Includes terrain, shielding and topographic multipliers for national coverage. Each multiplier further contains 8 directions.

Using the new release of the local wind multipliers software (V.3.1) (<a href="https://pid.geoscience.gov.au/dataset/ga/145699">eCat 145699</a>) and an appropriate source of classified terrain data, local wind multipliers on a national scale for the whole continent of Australia at (approximately) 25-metre resolution were calculated. This product is a necessary component for calculating local wind speeds from scenarios and guiding impact assessment of severe wind hazards for both federal and state-wide Emergency Services in Australia.

Wind multipliers are factors that transform regional wind speeds to local wind speeds considering local effects of land cover and topographic influences. It includes terrain, shielding, topographic and direction multipliers. Except for the direction multiplier whose value can be defined specifically by the Australian wind loading standard AS/NZS 1170.2, terrain, shielding and topographic multipliers are calculated using this software package based on the adaptations of formulae outlined in the AS/NZS 1170.2. This package is an upgraded version of wind multiplier computation software (<a href="https://pid.geoscience.gov.au/dataset/ga/82481">eCat 82481</a>) used to produce wind terrain, shielding and topographic multipliers for national coverage using an input of Land Cover Classification Scheme (LCCS) level 4 version 1.0.0 ( 2015) and 1-second SRTM level 2 derived digital elevation models (DEM-S) version 1.0. In order to improve the classification resolution in the built environment, the LCCS layer is overlaid with both mesh block and settlement types. The output is based on tiles with dimensions about 1 by 1 decimal degree in netCDF format. It includes terrain, shielding and topographic multiplier respectively. Each multiplier further contains 8 directions. The upgraded package is stored in Geoscience Australia public-facing repository and can be accessed via https://github.com/GeoscienceAustralia/Wind_Multipliers