Eurocode 1 Wind Peak Velocity Pressure

Calculation of peak velocity pressure qp depending on the basic wind velocity and the terrain category at the location of the structure. The wind action on the structure (forces and pressures) can be derived from the peak velocity pressure.
According to:
EN 1991-1-4:2005+A1:2010 Section 4
All Calculations
The basic wind velocity is given as vb = vb,0cdircseason where the fundamental value of basic wind velocity vb,0 is defined in EN1991-1-4 §4.2(1)P and its value is provided in the National Annex. The directional and season factors are generally cdir = 1.0 and cseason = 1.0. Values different than 1.0 may be specified in the National Annex for EN1991-1-4 §4.2(2)P
The terrain categories are illustrated in EN1991-1-4 Annex A (reproduced in the following figure). The transition zones between terrain categories are specified in EN1991-1-4 §A.2.
Wind terrain category 0 Wind terrain category I Wind terrain category II Wind terrain category III Wind terrain category IV
Illustration of Terrain categories reproduced from EN1991-1-4 Annex A
The appropriate reference height depending on the type of the structure is given in EN1991-1-4 Section 7

Orography factor different than 1.0 may be applicable over isolated hills and escarpments. See EN1991-1-4 §4.3.3 and §A.3 for more details.