What defines a semi-arid climate compared to an arid climate?

A semi-arid climate is defined by less extreme dry conditions compared to an arid climate, with more annual rainfall.

A semi-arid climate, also known as a steppe climate, is characterised by relatively low annual rainfall, typically between 250 and 500 millimetres. This is more than an arid climate, which receives less than 250 millimetres of rainfall per year. The semi-arid climate is often found on the edges of deserts or in the rain shadow of mountains, where precipitation is reduced.

In a semi-arid climate, evaporation often exceeds rainfall, but not to the same extent as in an arid climate. This means that while the landscape can be dry and vegetation sparse, it is not as extreme as in a desert environment. The vegetation in a semi-arid climate is typically made up of grasses and shrubs, adapted to survive in conditions of limited water availability.

Temperature-wise, semi-arid climates can vary greatly. They can experience hot summers and cold winters, or be relatively mild year-round, depending on their geographical location. For example, a semi-arid climate in a continental interior, far from the moderating influence of the sea, is likely to have a greater temperature range than a semi-arid climate near the coast.

In contrast, an arid climate, also known as a desert climate, is defined by extreme dryness. Rainfall is infrequent and insufficient to support most forms of plant life. The landscape is often barren, with sand dunes or rocky terrain. Temperatures in arid climates can be extremely hot during the day and drop sharply at night due to the lack of moisture in the air to retain the heat.

In summary, while both semi-arid and arid climates are characterised by low rainfall and high evaporation rates, a semi-arid climate is less extreme and can support more diverse forms of life.