The main factor determining the length of the rainy season in the savanna climate is the distance from the equator.

The savanna climate is characterized by distinct wet and dry seasons. It is typically found in tropical regions, where the annual rainfall is moderate to high and the temperature remains warm throughout the year. The length of the rainy season in the savanna climate is influenced by various factors, but the distance from the equator plays a significant role.

Distance from the Equator:
- The closer an area is to the equator, the longer its rainy season tends to be. This is because the equator receives more direct sunlight, resulting in higher temperatures and greater evaporation rates. As a result, there is more moisture available in the atmosphere, leading to more frequent and prolonged rainfall.

- As we move away from the equator towards the poles, the angle at which the sunlight reaches the Earth's surface becomes more oblique. This leads to lower temperatures and reduced evaporation rates, resulting in less moisture in the atmosphere. Consequently, the rainy season in savanna climates located further from the equator tends to be shorter.

- The distance from the equator also affects the intensity of the rainy season. Areas closer to the equator experience more intense rainfall during the wet season, while those further away may have more moderate rainfall.

Other Factors:
While distance from the equator is the primary factor determining the length of the rainy season in the savanna climate, other factors can also influence it to some extent:

- Latitude: Although closely related to distance from the equator, the latitude of an area plays a role in determining the length of the rainy season. Areas located in the tropical latitudes (around 0-30 degrees) generally have longer and more pronounced rainy seasons compared to those in subtropical latitudes (around 30-45 degrees).

- Altitude: Higher altitude areas tend to have shorter rainy seasons. This is because as air rises over mountains, it cools and releases its moisture, leading to precipitation. As a result, the air that descends on the other side of the mountains becomes drier, resulting in a shorter rainy season.

- Proximity to water bodies: Areas near large water bodies such as oceans or lakes may experience a longer rainy season due to the presence of moisture in the air. Water bodies contribute to the evaporation of water, increasing the humidity and the likelihood of rainfall.

In conclusion, while factors such as altitude and proximity to water bodies can influence the length of the rainy season in the savanna climate, the primary determinant is the distance from the equator. Areas closer to the equator tend to have longer and more intense rainy seasons, while those further away experience shorter and less intense periods of rainfall.