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Wind direction varies at different latitudes (distances from the equator). These winds, along with geography like mountains, will determine where rain falls. This affects both climate and where vegetation and deserts are. Understanding this helps world builders create sensible topography.

If our planet is tidally locked to the sun, it won’t rotate, one side burning and the other freezing. This extreme is not covered by this book, so we will assume our planet is rotating. On Earth, this rotation causes winds near the equator to travel east in the tropics, while winds in the temperate zones travel west. In the polar zones, winds are again eastward but are light. Technically, the westerly winds are not entirely westerly, as they move from near the equator toward the poles. Similarly, the easterly trade winds move toward the equator, not just easterly. Our invented planet can be rotating in the other direction, reversing these winds.

Figure 17 Prevailing Winds

Figure 17 Prevailing Winds

A continent situated in the northern hemisphere like the United States or Europe will have westerly prevailing winds, which are called the westerlies for that reason. The easterly winds are called trade winds; sailors used them to cross the world’s oceans, expanding trade. Ships benefit from sailing in the direction of the wind (prior to the invention of engines). We can call these winds what we want in our world, but it may only come up in the context of ship-oriented stories.

In areas with light winds, factors such as mountains, valley breezes, or the difference in air pressure between sea and land breezes affect wind patterns. These are local phenomenon and not something to consider when creating land features.

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