Mary Allen
During the rainy season, a lot of rain falls in an area. One only speaks of the rainy season when it occurs once or twice a year at the same time of the year. On a world map you can see: rainy seasons only occur in one strip on both sides of the equator.
In order for there to be a rainy season, the sun must be almost exactly vertical over the area at noon, i.e. exactly over the heads of the people. Due to solar radiation, a lot of water is released from the ground, from plants, or from the seas and lakes. It rises, cools far above, and then falls to the ground as rain.
In March the sun is above the equator, then there is a rainy season there. In June it is at its northernmost point, above the Tropic of Cancer. Then there is the rainy season. The sun then travels back over the equator bringing a second rainy season there in September. It migrates further south and brings a rainy season there in December over the Tropic of Cancer.
So, in the northern hemisphere near the equator, there is a rainy season in our summer. In the southern hemisphere near the equator, there is a rainy season in winter. There are two rainy seasons over the equator: one in our spring and one in our autumn.
However, this calculation is not always accurate. It also depends on how high the country is above sea level. The winds also play an important role, for example, the monsoon. This can also change the whole calculation significantly.
Near the equator, there is no real dry season between rainy seasons. There may be two months without rain, but that doesn’t mean the country is drying out. However, near the tropics, the dry season is very long, allowing the earth to really dry out. Further away from the equator there is no rainy season at all, for example in the Sahara desert.