Examination of Regional Wind Trends Due to Global Climate Change to Improve Wind Resource Assessments

In order to properly site arrays of wind turbines to achieve optimal wind power generation, estimation of the future mean wind speed for a given location is essential. In order to meet this need in the wind power energy, high-resolution spatial maps of the wind climatology have been created using climatological data and high-resolution numerical models. However, there is evidence that solely using climatological information as the basis of siting future wind turbines may not be a sound one because of the regional impacts of a changing global climate. It is now a well-accepted conclusion that the earth has become warmer over the last century. The Intergovernmental Panel on Climate Change (IPCC), (established by World Meteorological Organization (WMO) and United Nations Environment Programme (UNEP) to monitor climate), estimated the average surface temperature of the earth has increased during the last hundred years by about 0.6° ± 0.2°C. It is also generally accepted that at least part of this warming is due to the increase in greenhouse gasses emissions, primarily CO2. The scientific disagreements that do still exist primarily concern detailed aspects of the processes that make up these largely accepted general themes. The impacts of these warming trends are currently not being taken into account when examining wind power potential for a region.

The evidence for changing wind patterns because of global warming is consistent with theory. The generally accepted scenario for global warming is that the greatest impact will be the warming of the polar regions. The primary energy source for generating winds in the midlatitudes is the difference in temperatures between the polar and tropical airmasses. In theory, the reduction of the thermal difference between the polar regions and tropics should reduce the mean midlatitude wind speeds. There have been anecdotal wind trend studies done at a few locations that indicate that this may indeed be happening.

Even though the anecdotal wind studies tend to support the idea that wind speeds are decreasing in accordance with the theory of global warming, the impact of urbanization of an area could mimic this same trend. Wind speed is greatly reduced in urban areas versus open areas. The reduction in speed is typically on the order of 60% from a fully rural to fully urban land use. Also, the amount of reduction depends on the season. For example, trees in summer would tend to have more of a reduction effect than in the winter. It is possible that apparent changes in wind patterns are not actually due to global climate change but rather due to region changes in land use from rural forests and open fields to being highly urbanized.

MESO as contracted by AWS TrueWind has performed basic research that analyzed the Global NCAR-NCEP Reanalysis 50+ year data set and found global trends in the wind climatologies. High resolution simulations using the MASS and WRF mesoscale models are now being run over the past 50 year period for regions that show substantial changes in wind patterns. To ensure that the climatologies produced by the models are reasonable representation of the actual climatology changes, point observation wind climatologies will then be compared with the MASS and WRF generated and Reanalysis generated climatologies for the same point.

The results will be analyzed for the significance and implications to the wind power industry from both a global and regional perspective. It is important to understand the cause of the wind trends because the siting decisions would be fundamentally different if the cause for the change is different. If the wind trends are the result of global warming, this will change the general wind patters for entire regions of the globe. However, if the cause of the wind trends is primarily due to land use changes, the effect will be more localized and there would be ways to compensate for this within a given region. It would seem to be crucial to identify such trends and the true causes of such trends to avoid wasting (1) funds and (2) effort building wind turbines in non-productive locations.