To meet the growth in the deployment of wind energy technology worldwide, each year many tens of thousands of wind turbines sites must be assessed in terms of their wind conditions. The reduction of the cost of wind energy is strongly dependent on the ability to accurately estimate the wind resource and the design wind conditions. Many offshore and complex terrain wind farm projects are hampered by unforeseen wind conditions leading to difficulty estimating production and design conditions. Furthermore, uncertainties in the estimation of site wind condition, including those related to climate change, will also have consequences in risk analysis for building, operation, maintenance and dismantling phases of wind farms. In this sub-programme the purpose is to explore and align medium- and long-term research activities in order to lay the scientific foundation for more accurate estimation of wind conditions and climatic effects, through new measurement and modelling methodologies. Some specific challenges include: the increasing size of the very large wind turbines, the increasing size of very large wind farms and their interaction with environmental conditions, and the need to extend the new areas to install a wind farm regions challenging in terms of modelling and observational strategies such as deep waters and very complex terrain. Large scale deployment also implies deployment of long term infrastructure with life times longer than individual turbines. Therefore assessment of climatic effects plays increasingly stronger role. A cooperative effort between research centres will be essential to tackle the scientific questions poised in tackling these issues.