Aridity is a climatic phenomenon characterised by high temperatures and insufficient rainfall or very low rainfall. In the USA areas of less than 250mm of rainfall are regarded as arid areas. However in some parts of the world, the aridity may be measured differently e.g. in East Africa areas of less than 500mm may be regarded as arid. Areas of aridity are generally referred to as deserts or semi deserts and are characterised by dryness.
In East Africa areas that experience aridity include Northern Kenya, parts of Eastern Kenya, North Eastern Uganda, the Ankole – Masaka corridor parts of North Eastern Tanzania, Central Tanzania, parts of southern Kenya and parts of the western and the Eastern rift valley e.g. along Lake Albert, Lake Edward and Lake George.
Desert areas are those that may receive less than 250mm of rainfall and these may include areas in Northern Kenya e.g. around Ladwor in North Eastern Kenya and the Chalbi desert.
Besides this, there is also the Nyiri desert in Southern Kenya and the Masai steppe in North-Eastern Tanzania.
On the other hand, semi-desert areas experience relatively higher rainfall though less than 500mm.
CHARACTERISTICS OF ARID AREAS
- Low and seasonal rainfall is experienced. Drought is a common phenomenon in such areas.
- High temperatures are experienced i.e. temperatures of 30 °C and above.
- High diurnal range of temperature normally more than 15 °C i.e. during the day it is very hot and during the night is cold.
- There is generally low humidity. Relative humidity tends to be less than 20%.
- There is a limited cloud cover. Much of the year is characterized by clear skies.
- There are high transpiration rates and evaporation rates.
- There is unreliable or unpredictable rainfall.
- There is the occurrence of strong winds and occasionally dust storms are experienced.
- There is limited plant cover, this is because of the low rainfall such that the vegetation tends to be adapted to low rainfall conditions e.g. there are generally drought-resistant species such as steppe savannah grasslands, thicket, thorn bush, cactus, scrub, as well as patches of bare land.