Climate Characteristics

Precipitation

Precipitation in the HDB biome is usually between 0 and 250mm. Some receive less than 100mm. When rainfall does occur it can be unpredictable and often happens as convectional downpours. Evaporation is rapid and it may not have time to penetrate the soil.

high pressure belts

At the equator the sun is directly overhead and there are high levels of evaporation. This creates a low pressure zone where warm saturated air rises and high levels of precipitation take place. This air moves back toward the poles cools and sinks creating a high pressure zone of dry descending air. This contributes to the lack of cloud cover.

Trade winds

Trade winds move from these high pressure areas to low pressure at the equator. The cooler air is able to absorb moisture which reduces the level of precipitation. The Sahara desert is located where there is a high pressure belt and trade winds.

high diurnal temperature range

High pressure creates a lack of cloud cover and direct sunlight creates high temperatures. Daytime temperatures can be over 45'C. The lack of cloud cover at night means that heat escapes rapidly and temperatures can fall by as much as 30'C within 1 hour of sunset. Low temperatures at night time can cause fog or dew.

Cold ocean currents

Moisture laden winds move across the ocean. Cold ocean currents cool the prevailing winds, triggering rainfall over the sea. By the time the winds reach the land they are dry winds that absorb moisture, creating desert like conditions. The canary current is a cold ocean current beside the Sahara Desert.

The rain shadow effect

Precipitation takes place on the windward side of the mountains as warm air is forced upwards. On the other side (leeward side) cool dry air descends. The Gobi desert has been created in this way.

Continentality

In The Great Australian Desert, the winds have moved across land and they cannot absorb enough moisture or the precipitation has already taken place.