CLIMATE OUTLOOK FOR TANZANIA MARCH – MAY, 2012 RAINFALL SEASON
This statement gives a review of the performance of the October to December (OND), 2011 short
rainfall season , the ongoing seasonal rainfall over central, western, southwestern highlands, southern
and Southern coast, and an outlook for the March to May (MAM),2012 long rainfall season
(Masika).
A: SUMMARY
The performance of the October to December 2011 short rains (Vuli) faired well over most parts of
the country. However, both temporal and spatial distribution was not good in some areas. Towards
the end of the season in December some areas received heavy rainfall that caused catastrophic
disasters mainly over some parts of Dar es Salaam, Mara, Manyara, Mbeya, Arusha, Kilimanjaro,
and Mwanza regions. Few areas over the unimodal regions (i.e. Ruvuma, southern Morogoro,
Mtwara and southern Lindi) experienced poor OND, 2011 seasonal rainfall performance.
The outlook for the March to May, 2012 rainfall season indicates that most parts of the bimodal areas
are expected to receive normal to above normal rainfall except for Shinyanga region which is
expected to receive mainly normal rainfall. The ongoing seasonal rains over the unimodal areas are
expected to be mainly normal over most areas except for southern Iringa, Lindi, Ruvuma and Mtwara
regions that are expected to feature normal to below normal rains. These rains are expected to recede
towards the end of April, 2012. The principal contributing factors to the observed and predicted
weather include enhanced westerly wind flow, anomalous cooling of sea surface temperatures (SSTs)
over the central and eastern Atlantic Ocean and slight warming over Southwestern Indian Ocean.
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B: RAINFALL PERFORMANCE
The performance of the October to December (OND), 2011 short rains (Vuli) faired well over most
parts of the country. However, both temporal and spatial distribution was not good as some parts of
the country received much and heavy rains towards the end of the season. The recorded rainfall
amounts in millimeters for some selected stations with their respective percentages of long term
means in brackets are indicated below:
BIMODAL AREAS
Northern Coast and hinterlands: Tanga recorded 244.5 mm (280.8%), Pemba 389.2mm (189.5%),
Mlingano 557.9mm (336.7%), Handeni 164.4mm (68.9%), Kizimbani 282.7mm (95.8%), Zanzibar
342.0mm (96.4%), Morogoro 83.8mm (110.1%) and JNIA 469.9mm (94.2%) of rainfall.
Northeastern highlands: Moshi recorded 102.4mm (122.8%), Lyamungu 179.2mm (189.2%), Same
66.0mm (65.5%) and KIA 105.5mm (329.7%) of rainfall
Lake Victoria Basin: Mwanza recorded 247.2mm (113.2%), Bukoba 347.8 mm (128.8%), Musoma
142.8mm (117.8%) and Shinyanga 276.5mm (125.1%) of rainfall
UNIMODAL AREAS
Western areas: Tabora recorded 91.7 mm (63.2%) and Kigoma 202.2mm (101.1%) of rainfall.
Central areas: Dodoma recorded 38.2mm (51.8%), Hombolo 60.2mm (154.4%) and Singida
50.6mm (34.7%) of rainfall.
Southwestern highlands: Iringa recorded 141.3mm (94.1%), Mbeya 92.0mm (36.9%), Tukuyu
312.6 mm (253.7%) and Igeri 163.0mm (250.8%) of rainfall.
Southern areas: Mtwara recorded 81.7mm (70.0%), Kilwa 118.5mm (166.2%) and Songea 81.4mm
(169.6%) of rainfall
It should be noted that: Rainfall amounts below 75% of long term averages are categorized as
below normal while those ranging from 75 to 125% are categorized as near normal and those
greater than 125% of long term averages are categorized as above normal.
C: CLIMATE SYSTEMS OUTLOOK
This outlook is based on a review of the current and expected state of global climate systems and its
likely impacts on the upcoming March to May (MAM), 2012 rainfall seasons in the country.
Currently, the Sea Surface Temperatures (SSTs) in the equatorial central Pacific Ocean have been
anomalously cooler indicating persistence of weak La Niña conditions. However, slight warming
leading to neutral Sea Surface Temperature condition is projected towards the end of MAM, 2012
rainfall season.
The observed and projected cooling over Central equatorial and Eastern Atlantic Ocean coupled with
slight warming over the South-western Indian Ocean is expected to contribute and enhance westerly
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wind towards Tanzania leading to increased rainfall particularly over the western parts. Westerly
wave associated with phases of enhanced tropical convection is expected to move across the country
during the early period of the season (i.e. March) and thus influencing early rainfall onset.
The current weak temperature gradient between western and eastern parts of the Indian Ocean is
projected to persist through March, 2012 leading to weak easterlies towards East African coast.
The northern subtropical systems are projected to be relatively weaker than the southern systems that
suggest the possibility of fast retreat of the Inter Tropical Convergence Zone (ITCZ) from south to
north. Due to projected slight warming over South-western Indian Ocean and due to the likelihood of
factors favoring the development of tropical storms, the number of tropical storms is projected to
increase and this may have impact on the MAM seasonal rains.
D: SEASONAL RAINFALL OUTLOOK:
(i) Long Rainfall Season (Masika)
The long rainfall season in the northern sector (bimodal areas) of Tanzania is due to commence in
the first week of March, 2012. The details are as follows:
Lake Victoria basin: Rains are expected to start in the first week of March in Kagera and Mara
regions and gradually spreading over the rest of the basin during the second week. Most parts of
Lake Victoria Basin (Kagera, Mwanza and Mara) are likely to experience Normal to Above Normal
rainfall, while Shinyanga region is expected to receive normal rains.
Northern coast and hinterlands (Dar es Salaam, Tanga, Coast, northern Morogoro regions and
isles of Unguja and Pemba): Rains are expected to start during the first week of March. However,
some areas of this region had experienced pre-seasonal rains during the fourth week of February that
was associated with tropical storm over the Indian Ocean. The seasonal rains over this region are
likely to be normal to above normal.
Northeastern highlands (Kilimanjaro, Arusha and Manyara regions): The onset of rainfall is
expected during the first week of March, 2012 and the rains are likely to be Normal to Above
Normal
(ii) Seasonal Rains (the ongoing rainfall season)
Western areas (Kigoma, Tabora and Rukwa regions): The ongoing seasonal rains over these areas
are expected to be Normal to Above Normal except over Tabora and eastern Rukwa regions where
Normal rains are expected. These rains are expected to recede during the fourth week of April, 2012.
Central areas (Singida and Dodoma regions): The ongoing seasonal rains are expected to be
Normal to Above Normal over much of Dodoma, while Singida region is expected to feature Normal
rains. These rains are expected to recede during the second week of April 2012.
Southern coastal areas (Mtwara and Lindi regions): The ongoing seasonal rains in most of these
areas are expected to be Normal to Below Normal rainfall. Cessation of rains is expected towards the
end of the third week of April, 2012.
Southern areas (Ruvuma, Mtwara, and Lindi regions): The ongoing seasonal rains in these areas are
expected to be Normal to Below Normal. Cessation of the rains is expected during the third week of
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April, 2012.
Southwestern highland areas (Mbeya, Iringa and southern Morogoro regions): The ongoing
seasonal rains in most of these areas are expected to be Normal. However Southern Iringa and
Morogoro are likely to feature Normal to Below Normal rainfall. These rains are expected to end
during the third and fourth week of April, 2012.
It should be noted that heavy rainfall events are common even in below normal rainfall
conditions and periods of longer dry spells may occur even in areas with above normal rainfall. It
should also be noted that the March to May rainfall season is more significant for the northern
sector of the country.
Tanzania Meteorological Agency will continue to monitor developments of weather systems
including tropical cyclones over the southwestern Indian Ocean, which could influence the
rainfall patterns in the country and issue updates as necessary.
Figure 1: Rainfall Outlook for March to May 2012
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E: IMPACTS AND ADVISORY
Agriculture and food Security
Sufficient soil moisture condition is likely over much of the country, except for a few areas of
southern regions where earlier decline of soil moisture is anticipated during April 2012. The
expected above normal rains in bimodal rainfall areas are likely to cause excessive soil moisture
levels particularly over low ground areas, thus causing water log of crops.
Over northern coast, north eastern highlands, Lake Victoria basin and western (Kigoma), farmers are
advised to go for normal Masika cropping season. Over western (Tabora and Rukwa), central, southwestern
highlands and southern region farmers are advised to continue with normal practice as crops
get into maturity. Over unimodal areas crops like sweet potatoes, legumes, cassava and other short
term and drought resistance crops may benefit from the remaining rains in the season. However,
farmers are strongly advised to seek more advice from agricultural extension officers.
Energy and water
Water levels over the lakes, dams and rivers are expected to improve over areas where normal to
above normal rains are expected. Otherwise, an area where normal to below normal rainfall is likely,
no significant improvement on water levels is expected.
Pasture and Water for Livestock and wildlife
Pasture and water availability for livestock and wildlife over most parts of the country is likely to be
good. Pastoralists and agro-pastoralists are advised to harvest and conserve pasture for use during dry
periods. However, pastoralists and agro-pastoralists are strongly advised to seek more advice from
livestock extension officers.
Local Authorities
Municipals over areas where above normal rains are expected are advised to open up and clear
drainage systems to avoid water accumulation due to surface runoff so as to reduce the impacts of
heavy rains that may results into floods.
Health sector
Areas which are expected to receive normal to above normal rains, there is a likelihood of water born
diseases such as malaria epidemic and cholera outbreaks, thus necessary precautions should be taken.
Disaster Management
The disaster management authorities and other stakeholders are advised to take necessary measures
that would ensure preparedness, response, and mitigation of any negative impacts resulting from
expected weather conditions.
Released by Dr Agnes L Kijazi
DIRECTOR GENERAL, TANZANIA METEOROLOGICAL AGENCY (TMA)
3rd March, 2012