Roughness in Wind Atlas modelling

Roughness in the AROME high-resolution model

In AROME, roughness is represented as the area-weighted grid average. AROME has four main land cover classes: sea, lake, nature and town. The Charnook formula is used to calculate roughnesses for sea and lake. This approximation takes into account the effects of wind to wave height and thus also the effects on roughness length. For ice covered sea/lake, the roughness is constant at z0ice=10-3 m.

Nature includes 12 different vegetation types (see Table 1), called ISBA (Interaction between Soil Biosphere and Atmosphere). For most of these vegetation types, the roughness depends on: 1) LAI = Leaf Area Index, which is a climatological value that changes during the year; and 2) HT = Height of Trees, which varies from 30 m at the equator to 15 m in the temperate zone and up to 2 m at high latitudes.

AROME has nine different town types, but only one of these types is found in Finland. The roughness for this suburban type is constant at z0town=1 m.

Table 1. Roughness length for each ISBA vegetation type in AROME.

ISBA Vegetation types Z0
Bare soil 0..1
Bare rock 1
Permanent snow 0..01
Deciduous broad-leaved d HT
Needle leaved HT
Evergreen broad-leavede HT
C3 crops, wheat MIN(1, e(LAI-3.5)/1.3))
C4 crops, corn and sugar MIN(2.5, e(LAI-3.5)/1.3))
Irrigated crops, rice MIN(2.5, e(LAI-3.5)/1.3))
Temperate grassland LAI/6
Tropical grassland LAI/6
Wetlands, parks and gardens LAI/6

Roughness in WAsP modelling

For WAsP modelling we used the CORINE land cover 2000 map, published in 2004. This map, created by Finland's environmental administration (SYKE), includes land cover information in 25 x 25 metre resolution for the whole of Finland.

We determined aerodynamic roughnesses for each land cover type separately. These roughness values are based on the literature and are shown in Table 2.

Table 2. Roughness length for each CORINE land use type.

CORINE -classification z0 summer z0 winter Land use types
111 1.5 1.5 Continuous urban fabric
112 0.6 0.6 Discontinuous urban fabric
121 0.7 0.7 Industrial or commercial units
122 0.1 0.1 Road and rail networks and associated land
123 0.5 0.5 Port areas
124 0.02 0.02 Airports
131 0.1 0.1 Mineral extraction sites
132 0.1 0.1 Dump sites
133 0.3 0.3 Construction sites
141 0.4 0.4 Green urban areas
142 0.5 0.5 Summer houses
142 0.5 0.5 Sport and leisure facilities
211 0.03 0.001 Non-irrigated arable land
222 0.3 0.3 Fruit trees and berry plantations
231 0.03 0.001 Pastures
243 0.1 0.01 Land principally occupied by agriculture, with significant areas of natural vegetation
311 1.4 1.4 Broad-leaved forest
312 1.4 1.4 Coniferous forest
313 1.4 1.4 Mixed forest
321 0.05 0.001 Natural grassland
322 0.05 0.001 Moors and heathland
324 1.4 1.4 Sparse coniferous forest, cc. 10-30%
331 0.01 0.001 Beaches, dunes, and sand plains
332 0.05 0.05 Bare rock
333 0.2 0.2 Sparsely vegetated areas
411 0.1 0.1 Inland marshes
412 0.03 0.001 Peat bogs
412 0.03 0.001 Peat production areas
421 0.1 0.03 Coastal wetland
511 0.01 0.001 River
512 0.0004 0.001 Lake
523 0.0003 0.0007 Sea