Sudan Agromet Dekadal Bulletin
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Published by Sudan Meteorological Authority (SMA) Vol
2, Issue 19 11-20 September 2004 |
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Highlights |
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The ITCZ it moved southward last dekad position and the long term average.The current mean
position is about to 14°N. ·
Areas with heavier rainfall over ( 60 -100 mm) were found mainly in
the Southwestern and Eastern states of the country (West Equatouria, West and North Bahar Al Gazal, Warab,
Unity, Sennar and Blue Nile States .
Very low or no significant rainfall occurred in Northern and Southeastern
parts of the country. Almost all of these regions registered less than 20mm. · In relative terms Southern States, South Darfur, West Kordofan and Blue Nile States registered well above average rainfall, in contrast with West Darfur, South Kordofan, Upper Nile, Kassala and Gedarif States, where the rainfall amounts were markedly below the average. · North Sennar, White Nile, Gezaira and Kassala vegetation conditions are markedly below average. ·
In Southern Sudan, vegetation
conditions are mostly on average (Fig 4b) in broad accordance with the
rainfall situation but improvement vegetation conditions are noticeable in
East Equatoria, Lakes, Unity, Jonglei
and Upper Nile States. |
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Rainfall Analysis – Seasonal Progress |
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Rainfall in Sudan and its seasonal distribution is mostly the result of the northwards movement of moist air masses, source of the rainfall. The Intertropical Convergence Zone (ITCZ) marks the northernmost extent of these humid air masses, where they meet with drier and warmer air. The rains follow some distance south of this border between air masses, so that tracking this ITCZ through the season provides a quick evaluation of the seasonal movement of the rains |
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Fig 1a – Position of ITCZ over Africa in September Dek 2 2004 (red) compared to previous dekad (orange) and average position (black). Background is a rainfall map (Source : CPC-FEWS Net) |
Fig 1b – Current latitude of the ITCZ position compared to the 15 year average. (Source : CPC-FEWS Net) |
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Note (fig 1a) how the ITCZ position marks the border between the (significantly) rainy and non-rainy rainfall areas. The way this position changes along the season can be described by the time series of its mean latitude (fig 1b). We can see : · The ITCZ has been South of the average position for this dekad. · This dekad, it moved southward. (see Fig 1). The current mean position is about to 14°N. |
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Rainfall Analysis - Dekadal Amounts and Frequency |
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10 day rainfall amounts produced by SAMIS at SMA/SEWS are based on a combination of METEOSAT satellite and synoptic gauge data. Rainfall climatology is similarly derived from a combination of historical data from the two sources. |
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Fig 2a – Rainfall amounts (mm) 11-20 September 2004 |
Fig 2b – Same but in relative terms : as % of long term average |
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In this dekad, the ITCZ shifted to south from its previous dekad position, the rainfall amounts were generally much higher than previous dekad. Areas with heavier rainfall (over 60 -100 mm) were found mainly in the Southwestern and Eastern states of the country (West Equatouria, West and North Bahar Al Gazal, Warab, Unity, Sennar and Blue Nile States) with point values reaching 100.2 mm reported at Wau, 72.9 mm reported at Damazine , 64.6 mm reported at Babanusa and 54.8 mm reported at Kadugli. In contrast, very low or no significant rainfall occurred in Northern and Southeastern parts of the country. Almost all of these regions registered less than 20mm. |
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In relative terms Southern States, South Darfur, West Kordofan and Blue Nile States registered well above average rainfall, in contrast with West Darfur, South Kordofan, Upper Nile, Kassala and Gedarif States, where the rainfall amounts were markedly below the average. |
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Rainfall Analysis - Cumulative Amounts |
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Cumulative amounts are obtained by summing the dekadal estimates starting from Dekad 1 of March until present. |
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Fig 3a – Cumulative rainfall (Mar Dek1 – Current Dek) |
Fig 3b – Same but in relative terms : % of long term average |
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The cumulative rainfall amounts (Fig 3a) display the usual organisation in latitude bands (as the rainfall moves north following the ITCZ). Currently, values approach 1000 mm in southernmost Sudan and less than 50mm up to 18°N. |
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The situation relative to the average (Fig 3b) has not changed much from last dekad in many parts of Sudan. The belt of below average conditions now includes North Darfur, Greater Kordfan, Unity, Warab, White Nile, Gedaref, Sennar and western parts of West Equatoria States. Elsewhere, in the South (East Equatoria, Bah Al Jabal, parts of Upper Nile and Jungolei States) and in parts of Western Sudan (northern parts of West Darfur and western parts of South Darfur) the situation is close to the average or above. |
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Vegetation Analysis |
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Vegetation information is based on the NDVI, a satellite index related to vegetation amount and vigour. NDVI data is sourced from the Africa Data Dissemination Service and processed at SMA. |
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Fig 4a – NDVI 11-20 September 2004. Darker shades for denser vegetation, lightest shade for soil. (Source : ADDS). |
Fig 4b – Same in relative terms : % of long term average (ADDS) |
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The NDVI for this dekad (Fig 4a) continues the trend of vegetation advancing northwards following the progress of the rains. Currently, new season vegetation development is registered in the central States, up to the borders of Sennar, Gedaref, South and West Kordofan and West and South Darfur. In Southern Sudan, vegetation conditions are mostly on average (Fig 4b) in broad accordance with the rainfall situation but improvement vegetation conditions are noticeable in East Equatoria, Lakes, Unity, Jonglei and Upper Nile States. North Sennar, White Nile, Gezaira and Kassala vegetation conditions are markedly below average. The indications from the vegetation index and rainfall estimates imply that early season vegetation development is somewhat delayed due to poor or irregular rains. However some improvements are already noticeable in West and South Darfur, West and South Kordfan, Blue Nile, Sennar and Gedaref States but these are dependent on good rains during the rest of the season. |
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Acknowledgements |
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WFP Khartoum funded the installation of technical capacity and provision of training at SMA (Sudan Meteorological Authority) in the shape of SAMIS/SD – Satellite based Agro Meteorological Information System / Sudan. This is an operational system for the local production of satellite and station based rainfall and vegetation information for distribution to a wide range of local users. The system was prepared and installed by the TAMSAT group of the Department of Meteorology, Univ of Reading, UK. For information, please contact Dr. Rogério Bonifácio at : tamsat@rdg.ac.uk or rbonifacio@mail.telepac.pt |
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Contacts |
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The SAMIS team includes : Mr. Mousa Abdelbagi / Mrs. Hanan Awad Mohamed / Mrs. Badria Abdel Rahman For further information, please contact Dr. F. K. El-Sayem, Director General Sudan
Meteorological Authority PO
Box 574, Khartoum Sudan Tel. +249 11 778836/7 Fax. +249 11 771693 Contact : su_samis@yahoo.com / ersad@sudanmail.net.sd |