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The climate of Uganda Notes

Climate refers to average weather conditions of a place which is measured and recorded for a very long time usually between 35 and 40 years.

Climate is determined when weather elements are measured and recorded. Such elements include;

  • Rainfall measured by a rain gauge.
  • Temperature by the sixth thermometer
  • Humidity by hygrometer
  • Atmospheric pressure by a barometer
  • Sun shine by a Campbell stock
  • Cloud cover by hydrogen filled baloons
  • Wind strength by anemometer
  • Wind direction by wind vane.

These elements of weather are measure at a weather station at Entebbe-Wakiso district.

Climatic belts of Uganda.

Uganda is supposed to have an equatorial climate by virtue of its location astride the equator, but because of its relief and other factors it experiences;

  • Equatorial climate
  • Modified equatorial climate
  • Tropical climate
  • Mountain climate
  • Semi-desert climate

 

 

 

 

 

The climatic regions of Uganda

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Equatorial climate

This is experienced around Victoria shores i.e. Kampala, Kalangara, Entebbe, etc. It has got the below characteristics;

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  • Heavy rainfall over 1250mm per annum. This rainfall is reliable and well distributed throughout the year because of breezes.
  • Hot and humid temperatures ranging between 220C-300C due to thick cloud cover in the region
  • High humidity throughout the year due to high evaporation rates in the region.
  • Small annual temperature range between 00C-30C due to hot and humid temperatures received throughout the year.
  • There is little or no dry season with one rainfall peak, although areas away from L. Victoria can experience two distinctive rainfall peaks, this is due to high humidity received throughout the year.
  • The climate is warm and wet and leads to growth of equatorial rain forests of Mabira and Ssese.

Modified equatorial climate

This is experienced in West Nile, Kigezi highlands and some parts of central Uganda, with the below characteristics;

  • Relatively heavy rainfall between 1000mm and 1500mm per annum mainly relief rainfall.
  • There is alternating dry and wet seasons
  • High humidity during the wet season and low humidity during dry season.
  • High temperatures are experienced above 250C throughout the year
  • Rainfall received is of two rainfall peaks
  • Mostly the climate leads to growth of savannah woodlands.

Tropical climate

This covers the most parts of Uganda more especially in the northern region with the following characteristics;

  • It has a clear distinct wet and dry seasons
  • Moderate rainfall is received between 750mm-1000mm per year due to moderate humidity received in the region.
  • High temperatures are experienced ranging between 250C-320C throughout the year.
  • High humidity during the wet season and low humidity during the dry season.
  • The climate leads to growth of savannah vegetation dominated by grasslands.

Semi-desert

This is experienced in north eastern Uganda i.e. Moroto, Kotido, Kaabong and in Albert eastern shores i.e. Kabalega park and in Ankole-Masaka corridor. It has the following characteristics;

  • Very low rainfall is received between 325mm-620mm per year due to low humidity in the region. It has one rainfall peak
  • Very hot temperatures are experienced over 350C due to cloudless skies.
  • Very low humidity in such areas and the skies are cloudless thus hot days and clold nights.
  • The climate leads to the growth of shrub and thickets due to low rainfall.

Factors which influence the climate of Uganda

Relief, highland areas like Mt. Rwenzori block moving moist air masses resulting into the formation of relief rainfall on the wind ward side of the mountain while little or no rain is received on the lee ward side due to descending dry winds as illustrated.


Image From EcoleBooks.com

This explains why some parts of Kasese receive little rainfall well as Semulik valley receives heavy rainfall.

Flat areas like Karmoja receive little rainfall because of lack of obstacles to make the winds rise.

Altitude has an effect on temperature in Uganda. Places of high altitudes like Rwenzori peak, Elgon, experiences low temperatures while lower altitudes of Albert shores and rift valley areas experiences high temperature. This is because the higher you go upslope, the cooler it becomes.

Water body effect, large lakes such as Victoria and Kyoga are source of water vapour in atmosphere through the high rates of evaporation. This results into high humidity content in atmosphere thus convectional rainfall as illustrated.

Image From EcoleBooks.com

Such lakes also influence rainfall formation on their crescent due to land and sea breeze.

Latitudinal effect, Uganda is located astride the equator and this makes it to receive high temperature throughout the year. The high temperature received warm up air masses on the ground causing them to rise, condense and form convectional rainfall. This is experienced around l. Victoria, western and south western and northern parts of Uganda.

Nature of vegetation cover, areas covered by forests like Mabira, Kalinju influence convectional rainfall formation due to the process of evapo-transpiration. On the other hand areas with shrubs and thickets vegetation such as Karamoja and Ankole-Masaka dry corridor receive very low rainfall since such vegetation provide limited water vapour in the atmosphere for rain formation.

The prevailing wind system effect, Uganda is affected by two main wind systems i.e. the north east trade winds and the south east trade winds. These winds are caused by the apparent movement of the sun north and south of the equator.

When the sun moves to the tropic of Capricorn, the north east trades blow with a lot of emphasis over Karamoja and make it dry due to no obstacle to make them rise. They pick moist air from L. Kyoga and cause rainfall at the foothills of Mt. Rwenzori in Fort Portal.

As they reach the equator, are deflected to the left and help to dry up Ankole-Masaka corridor as it also lack physical obstacle to make them rise.

When the sun moves to the tropic of Cancer, the south east trades blow and pick moist air from Victoria and cause rainfall on the northern shores of L. Victoria. They also blow over Ankole-Masaka corridor and dry it further and cause rainfall in western Uganda.

As they reach the equator, are deflected to the right, moves through L. Kyoga and help to dry up Karamoja again.However a section of these winds bring about rainfall formation on Mt. Elgon and Moroto in eastern Uganda.

When the sun is on the equator, the winds i.e. NE and SE trades converge and cause cyclonic rainfall.

Map of Uganda showing wind systems.

Image From EcoleBooks.com

 

 

The effect of westerlies, these winds blow from Congo basin towards Kasese, Bundibugyo, Kabalore, Kisoro and Bushenyi. These warm and moist winds are blocked by the highlands of south western Uganda, rise, condense and form relief rainfall.

Position of the sun overhead, since Uganda is located astride the equator, it experiences the periods of equinoxes i.e. March and May and also September to October. Throughout these periods the country experiences heavy rainfall due to inter-tropical convergence zone (ITCZ).

Man’s activities, which effect climate positively and negatively i.e. activities such as deforestation, monoculture, swamp reclamation, settlement, overgrazing, tend to affect vegetation thus less water vapour in the atmosphere and less rainfall.

Man has tried to improve on the climate of the area by programs such as aforestation and reforestation as in Kabale, Ntugamo and Mbarara. This Increases the chances of rainfall formation and climatic modification.

 

Rainfall patterns in Uganda.

Rainfall refers to tiny droplets falling on the earth’s surface from the atmosphere under the influence of gravity. There are mainly two rainfall types received in Uganda i.e.

Relief or orographic rainfall characterized in mountainous or hilly areas of Uganda like Rwenzori.

Convectional rainfall commonly received in areas of water bodies of Victoria and Kyoga and dense forests like Mabira and Kalangala forests.

Rainfall distribution in Uganda

The rainfall received in Uganda is generally grouped as;

Rainfall above 2000mm experienced in equatorial climatic regions like on L. Victoria crescent.

Rainfall ranging between 1500mm-2000mm (heavy) experienced in modified climatic regions of Uganda.

Rainfall ranging from 1000mm-1500mm (medium) experienced in tropical climatic regions like in northern Uganda.

Rainfall ranging between 750mm-1000mm (low) experienced in semi-arid climatic regions like in Lyantonde, Kiruhura, Lwengo, etc.

Rainfall ranging below 750mm per annum experienced in dry climatic regions like in Karamoja districts of Kaabong, Kotido Kitgum, etc

The distribution of rainfall in Uganda

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Factors for the variation in rainfall distribution in Uganda

  • Relief, in mountainous areas like Rwennzori in Kabarole, Bundibugyo receive heavy rainfall of about 1500mm per annum. This is because mountains block moist winds on the wind ward sides which rise, condense and form rainfall.
  • The areas with dense forests like Mabira in Buikwe receive heavy rainfall due to high evapotranspiration levels resulting into convectional rainfall.
  • Areas near large water bodies like the shores of L. Victoria in Kampala, Wakiso, receive heavy rainfall over 1500mm per annum due to lake and land breezes.
  • Latitudinal influence/I.T .C.Z, this is a low pressure belt where various winds meet resulting into heavey thunder stoms and rainfall around lake Victoria region in districts of kamuli, Iganga Kampala where heavy rainfall of about 1500mm p.a is received.
  • Wind system, the northeast trade winds bring dry conditions because they originate from the dry desert. This has resulted into dry conditions (less than 750mm) in kotido and moroto. The south east trade winds from the Indian ocean carry moist winds which they drop on the slopes of mountain Elgon resulting into heavy rainfall(1500mm) in sironko and Manafwa.
  • Destruction of vegetation cover, in areas where vegetation has been destroyed the rainfall amounts have reduced eg Nakasongola with less than 750mm pa.
  • Afforestation and re-afforestation in areas where trees have been planted the rainfall amounts have been increased such as Kabale(mafuga forest), bugamba in Mbarara etc.
  • Swamp drainage / reclamation in areas where swamps have been reclaimed.The rainfall amounts have been reduced because of evaporation e.g in Kumi, Soroti, Bugiri etc.
  • Mam made lakes/ valleys dams/ ponds, when these are constructed they increase on evaporation levels and therefore results into increased rainfall amounts such as kibimba.
  • Government policy of conservation



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