Posted on January 27, 2022

Windiness across Ireland in 2021 – a low wind year

The BrightWind Wind Map shows that annual wind speeds in 2021 were 4-10% lower than the long-term average across the island of Ireland.

How windy was last year relatively speaking? The BrightWind Wind Map shows the windiness of 2021 by comparing mean wind speeds around the country with their long-term average.

The BrightWind Wind Map – what is it?

The BrightWind Wind Map is a visual representation of the windiness in 2021. Windiness, or a wind index, provides a comparative measure of wind speeds during a short-term period relative to the long-term. It is calculated as the short-term mean wind speed normalised by the mean during a long-term period.

The Wind Map is based on a 120-node mesh of MERRA-2 reanalysis data created by NASA. Reanalysis datasets are an assimilation of current meteorological observations with past short-range forecasts constrained by previous observations. They provide a continuous record of climatic conditions across the globe at any given time.

Both the short- and long-term periods used for the wind map consist of MERRA-2 data. The long-term period is 2000-2020.

The BrightWind Wind Map – what does it show?

Ireland as a whole
Last year was a low wind year across Ireland with wind speeds being down 4-10% when compared to the long-term average. Looking at Ireland as a whole, the mean wind speed is just 94% of the long-term – a large drop compared to 2020’s high of 106% and the second worst year over the last 21 years, with only 2010 being lower.

Windiness by region
The Wind Map shows the spatial variation in windiness, with the lowest relative wind speeds reported in the north of the country and increasing towards the south-west. Below is a comparison of the following 5 areas – Donegal, Cavan, Galway, Carlow, and Kerry.

In each of these areas, the windiness is analysed on a monthly basis relative to the long-term period while adjusting for seasonal effects. Seasonal adjustments are based on similar calendar months. For example data from January 2021 is normalised against all Januarys in the long-term period. The results are plotted below.

While there are some variations between the locations, the general trend is the same. A weak January was counteracted by unusually high wind speeds in February. These reduced to lows in July, which included the lowest monthly wind speeds in 20 years, and finally climbed back to near-typical wind speeds by the end of the year.

So how have your assets performed in the context of the lower winds speeds of 2021? Contact me ( to help you find out.

Windiness in Donegal

Windiness in Cavan

Windiness in Galway

Windiness in Carlow

Windiness in Kerry