A month by month map of the world's winds: the trade winds, the westerlies, the Roaring Forties and the monsoon that turns around each year. Where are the windiest places on land, how much does the wind change with the seasons, and do the world's wind farms actually sit where the wind is?
Wind is air on its way from high pressure to low, bent by the spin of the Earth and slowed by the ground it rubs against. Over the year that restless air settles into patterns old enough to have names: the trade winds that carried sailing ships west across the tropics, the westerlies that brought them home, the Roaring Forties of the Southern Ocean, and the monsoon, which blows one way in winter and the other in summer.
I mapped them. Over land I used WorldClim's monthly averages of wind speed 10 m above the ground, in cells about 9 km across. For the oceans and for direction I used the NCEP/NCAR reanalysis, a weather model fed with three decades of observations. Then I asked three questions. Where are the windiest places? How much does the wind change with the seasons? And do the world's wind farms actually stand where the wind blows? Mostly they do: 82% of onshore wind farm capacity in the WRI power plant database sits on ground windier than its country's median.
Move the slider to see each month, or press play. The moving lines show which way the near-surface wind blows on average in that month; they are drawn from the coarse reanalysis grid, so they show the great streams rather than the gusts in any one valley. "Seasonality" shows how much stronger the windiest month is than the calmest. Click anywhere for its numbers, and switch on the wind farms to see where they stand.
Seen from far enough away, the world's winds are a set of belts. Between about 7.5° and 22.5° of latitude the oceans carry the trade winds, blowing towards the equator and to the west: from the north-east in the northern hemisphere and from the south-east in the southern. Over those oceans they average 6.7 m/s in the north and 7.0 m/s in the south. What makes them special is their steadiness. If the wind always blew from exactly the same direction, its average as an arrow would equal its average speed. In the trades the arrow keeps 76% of the speed. In the northern westerlies, between 40° and 55° N, where storm after storm swings the wind around, it keeps only 38%.
The strongest belt is in the far south, where nothing but the tip of South America interrupts the westerlies all the way round the world. Over the oceans between 40° and 50° S, the Roaring Forties, the wind averages 10.2 m/s, against 8.8 m/s at the same latitudes in the north. The fastest band of all is around 52.5° S, the Furious Fifties, at 11.4 m/s, and the windiest 2.5° cell of open ocean, south of the Indian Ocean at 50.0° S, averages 12.6 m/s. The southern belt also keeps going all year. In January the northern oceans at 40° to 50° N are actually windier (10.3 m/s against 9.5), but in July they calm to 6.9 m/s while the Forties blow at 10.9.
Over the oceans the wind averages 7.6 m/s between 60° N and 60° S. Over solid land, in the same reanalysis, it averages 3.8.
In the northern Arabian Sea the wind changes sides with the seasons. In January the average wind there comes from the north-east at 6.3 m/s, dry air flowing off Asia. By July it comes from the south-west at 11.7 m/s, wet air pulled in towards the heated land of India. Off the Horn of Africa it strengthens into a low-level jet: the July wind there averages 13.6 m/s. The Bay of Bengal does the same, from the north-east in January and the south-west in July. Press the Monsoon button on the map to watch it.
The Indian Ocean is the largest example but not the only one. Taking any 2.5° cell where the January and July winds both average at least 2 m/s as an arrow and point at least 135° apart, 12% of the area between 60° N and 60° S reverses its wind between winter and summer. The reversing cells run across the northern Indian Ocean and southern Asia, West Africa, Indonesia and northern Australia, and the seas off East Asia, with a few more where the subtropical high pressure belts shift north and south with the seasons, near 35° N in the Pacific and 32° S in the southern oceans.
Over land, wind is much weaker than at sea, because hills, forests and buildings drag on it. The average across the world's land outside Antarctica is 2.9 m/s at 10 m. Only 5% of that land averages 5 m/s or more, and a quarter of it (25%) averages less than 2 m/s, mostly in the still air of the rainforests and sheltered basins.
The windiest cell outside Antarctica, at 15.8 m/s, is on the Vatnajökull ice cap in Iceland, where cold air drains off the ice. Of all the countries and territories bigger than 50,000 km², Iceland is also the windiest, at 6.7 m/s on average; the calmest is the Republic of the Congo, at 1.1. The rest of the top of the list is ice and ocean islands: Jan Mayen, the Greenland ice sheet, the Patagonian ice fields, Tierra del Fuego, and the specks of land in the Southern Ocean such as Heard, Macquarie, Bouvet and Kerguelen. Antarctica itself is windier still: its coast reaches 20.0 m/s in WorldClim. These are also the places with the fewest weather stations, so their numbers are the least certain on the map.
Among the 505 cities of a million or more people in Natural Earth, the windiest is Marseille (5.8 m/s), funnel of the mistral, then The Hague (5.6), Melbourne, Auckland and Adelaide. The calmest are in the tropical highlands and sheltered valleys: Bogotá (0.9 m/s), Cali, Srinagar, Medellín and Mandalay.
On northern land the windiest month, on average, is April and the calmest is August. That surprised me: I expected winter. But in spring the land warms fast while the sea and the poles stay cold, and the strong contrast drives the wind; in winter much of the northern interior lies under still, cold air. Across the land north of the tropics, 57% has its windiest month in March, April or May, and 28% in April alone. In the south the windiest month is October, again spring, and the calmest May.
For most places the swing is modest. Over land where the average wind is at least 1.5 m/s, the median ratio of the windiest month to the calmest is 1.48, and only 8% of that land has a windiest month twice as windy as its calmest. The strongly seasonal places are of two kinds. In the interior of Siberia, Mongolia and the Yukon, winter air lies dead calm under the great cold high pressure of Asia and North America, and the wind wakes up in May. And on the monsoon coasts, Kutch and Odisha in India, the Maldives and the Chagos islands, the wind blows hard in the wet season and drops away in the dry. Sistan, on the border of Afghanistan and Iran, has its own summer wind, the "wind of 120 days".
The World Resources Institute's Global Power Plant Database lists 5,344 wind farms with 263 gigawatts of capacity in 58 countries. It is a 2021 snapshot, so it misses everything built since, and its coverage is uneven: the United States, China and the UK make up 68% of the capacity, while countries such as Germany and India appear with a small fraction of their real fleets. So it can say where the listed farms are, not how much wind power a country has.
For each farm on land I read the WorldClim wind at its site and asked how windy that is compared with the rest of its country. Weighting each farm by its capacity, the average farm stands on ground windier than 72% of its country's land. 82% of the capacity is on the windier half of the land and 53% on the windiest quarter. In 17 of the 21 countries with at least 400 MW across 8 or more listed farms on land, the farms are windier on average than the country as a whole.
The clearest cases are countries where good wind is rare and concentrated. Mexico's farms crowd into the Isthmus of Tehuantepec in Oaxaca, a gap in the mountains where the wind is squeezed between the Gulf and the Pacific: they stand on ground windier than 98% of the country. Brazil's farms mostly line the windy north-east coast at 2.4 m/s, against 1.5 for the country. In the United States the farms average 4.4 m/s against 3.6 for the lower 48 states, most of them on the windy Great Plains from Texas to Iowa; in China 3.4 against 2.7, led by Inner Mongolia and Gansu.
A few countries go the other way, and for understandable reasons. Chile's farms (3.4 m/s) are in the north and centre, near people and the grid, while its windiest land is in empty Patagonia. In the UK the farms are only a little windier than the land as a whole (5.2 against 4.9 m/s), because Britain's windiest ground is its islands and mountain tops, and because much of its newest wind is at sea. Germany is listed with only 13 large onshore farms, too few to judge.
The UK is one of the windiest countries on Earth: of those bigger than 50,000 km², only Iceland, Greenland and Western Sahara are windier. Its land averages 4.9 m/s at 10 m, 1.7 times the world's land average, and 41% of it averages 5 m/s or more. Scotland is windiest at 5.6 m/s; England (4.6), Wales (4.6) and Northern Ireland (4.6) are close together, and Ireland averages 4.6. The windiest cell in the UK is St Kilda, far out in the Atlantic, at 8.9 m/s.
The windiest counties are the Scottish islands: Shetland (7.6 m/s), the Western Isles, Orkney, then Argyll and Bute and North Ayrshire. England's windiest is Cornwall (6.0), followed by Cumbria and the East Riding of Yorkshire. The calmest lie in the sheltered west Midlands and the Welsh borders: Herefordshire (3.3), Shropshire and Worcestershire. British wind is a winter wind: January averages 5.9 m/s and August 4.1.
The database lists 780 UK wind farms with 23.2 GW, 32% of it at sea, led by Hornsea 1 off Yorkshire at 1,200 MW. On land, Scotland holds 61% of the onshore capacity, most of all in Highland, then Northern Ireland and South Lanarkshire.
Wind over land. WorldClim 2.1 (Fick and Hijmans 2017) gives the average wind speed 10 m above the ground for each month of 1970 to 2000, interpolated from weather stations, at 5 arc minutes (about 9 km). The annual mean is the mean of the twelve months. I left out 10,196 cells with no Natural Earth land within one cell, mostly over the Caspian Sea, and, when measuring seasonality, 3,634 cells with one impossible month (a value less than a third, or more than two and a half times, the average of the months either side), which look like faulty station records. Averages over areas are weighted by the area of each cell. WorldClim's grids may not be redistributed, so the map shows them only as pictures in colour classes, and the values you get by clicking come from a coarse summary: the mean of each 0.5° square, rounded to 0.5 m/s.
Direction and the oceans. The NCEP/NCAR Reanalysis 1 (Kalnay and others 1996) combines observations with a weather model. I used its long-term monthly means for 1991 to 2020 at the lowest model level (sigma 0.995, roughly the lowest 40 m), on a 2.5° grid: the west to east and south to north wind, and the mean daily wind speed. Ocean averages use cells with less than 10% land. The reanalysis is higher up, coarser and from a later period than WorldClim, so it reads windier: over 2,017 cells of solid land it is a median 1.39 times WorldClim, though the two agree on where it is windy (correlation 0.79). That is why the sea is drawn fainter on the map.
Wind farms. The WRI Global Power Plant Database v1.3 (2021), rows with primary fuel "Wind". A farm counts as on land if its point falls in a WorldClim land cell; on the coast if not, but a land cell is next to it (its wind is then the mean of those cells); otherwise at sea. For each country the land average leaves out overseas territories without listed farms (so the United States means the lower 48 states). A farm's percentile is the share of its country's land, by area, that is less windy than its cell.
Limits. The wind at 10 m is not the wind at a turbine hub, 80 to 150 m up, and a 9 km cell cannot see the hilltop or ridge a farm is built on, so farms are probably windier than these numbers say. WorldClim is smoothest where stations are fewest: ice caps, deserts, mountains and remote islands. The monthly means hide gusts, storms and calm spells, which matter more for power than averages. The power plant database is a 2021 snapshot with uneven coverage.