20.1. Seasonal Distribution of Rainfall

The conditions, which can cause precipitation, do not exist in the same combination throughout the year. This leads to the variations in the seasonal distribution of rainfall. However, most of the areas in the world receive a major part of the precipitation during the summer season.

The main characteristics of the seasonal distribution of rainfall

♤ Heavy rainfall occurs throughout the year in the equatorial region.

♤ A few degrees north or south of the equator have wet summers and dry winters.

♤ The monsoon circulation brings more seasonal contrasts resulting in wet summers, as the wind blows onshore, and dry winters as the wind blows offshore.

♤ Seasonal variation, due to the monsoons, is well-developed in the Indian Subcontinent and in Southeast Asia.

♤ Most of the western coastal areas in the mid- latitudes have dry summers and wet winters due to the presence of the sub-tropical high pressure belts.

♤ In the temperate region the precipitation is cyclonic in nature and the cyclones are more common in the winter season. Thus heavy rainfall occurs in winters and not in summers.

The monthly distribution of precipitation throughout the year is often more significant than the average annual precipitation because rainfall is important for the various human activities, especially agriculture. The dependence on rainfall is a matter of great concern to farmers in the sub-humid and semi-arid lands where any departure from the normal regime may result in crop failure.