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.
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 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 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.
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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, south-western 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.
DIRECTOR GENERAL
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