Rainfall in Sudan mostly results from northwards movement of humid air masses from March to August and their southwards retreat from September to November. At their northernmost reach, these humid air masses meet with drier and warmer air to form the InterTropical Front (ITF). Since the rains follow south of the ITF, the seasonal progress of the rainy season and of its quality can be evaluated by tracking the ITF. Fig 1(a) shows a map with the latest ITF position, the previous position and the usual position, while Fig 1(b) shows a plot with the average position over Sudan from the beginning of the season.

The current ITF position is on the average and it is markedly southwards of its position in the previous dekad.

The strong early northwards movement of the ITF in April lead to widespread rainfall reaching northern locations such as El Geneina, Wad Medani and Kassala by mid month and further unusual rainfall at end of April in Eastern and Central Sudan. But as a consequence of the southwards retreat of ITF in early May we see a corresponding southwards retreat of the rainfall in this period.

April and Early May Rainfall in Sudan

During April, significant rainfall was confined to Southwestern Sudan. Higher amounts were registered in the border regions, along south of Western Equatoria and Central Equatoria. Fairly low amounts were registered in East Equatoria and central-southern Jonglei (see Fig 2a). In these southeastern regions, the April rainfall was about 50% of the normal.

In April, widespread but light rainfall was reported in East and Central Sudan because of strong early northwards movement of the ITF. This very early rainfall did not have continuation in early May.

In early May, in contrast, rainfall everywhere across Sudan was low (see Fig 2b) and limited to Southern Sudan. Except for localised higher amounts such as in SW Lakes state and areas N of Juba, maximum amounts were around 30mm in the wetter regions, about 60% of the average for this time. Elsewhere,  amounts were lower, down to 40% of the average or less. 

The total rainfall from the beginning of the season (Fig 2c) has been above average in west, central and eastern Sudan, due to the unusually early rainfall. Impact of this is minimal as it is too early for most agricultural activities.

 In Southern Sudan the situation is mixed, with on or above average rainfall in Greater Bahr-el-Ghazal, Warab, Unity and northern Jonglei and Upper Nile. In contrast, East Equatoria and Southern Jonglei have been suffering below average rainfall (40%-60% of the average). In these regions, the low rainfall during the early season is likely to have caused problems to the start of the agricultural activities, ruling out early planting of long maturing sorghum varieties.

May rainfall is key for the planting of the long maturing sorghum across most of South Sudan and rainfall needs to improve in the rest of the month in order for the agricultural season to get off to a good start.

Vegetation Status

Vegetation condition and development are assessed by means of the NDVI (Normalized Difference Vegetation Index) – this is a satellite derived parameter which responds (almost) uniquely to vegetation and is available on a global scale every ten days.

Vegetation has been extending northwards from early April to early May (Fig3 a,b), reached South Kordofan, Upper Nile, Blue Nile and even noticeable in South Darfur. On other hand, higher greenness in West Equatoria, along the border with Uganda, highlands of East Equatoria and southeastern Jonglei. There was some gaps in greenness in Jonglei and East Equatoria as a consequence of low rainfall until now.                                                                                                                                                                                          

In terms of variations from average : we notice above average vegetation across Greater Bahr El Gazal, Warab and Lakes as well as northern Unity, South Kordofan and areas of Upper and Blue Nile. Comparing Fig 4 with Fig 2c it is clear this results from widespread early rainfall across these regions, leading to an earlier than usual start of the growing season. In contrast, lower than average vegetation in southwest Jonglei and borders with East Equatoria results from lower than average rainfall in these regions (Fig4).

The Wheat Crop 2007-2008

Wheat is grown as an irrigated crop during Winter (December to March) in several irrigation perimeters across Northern Sudan. The major producing areas are spread along the (White) Nile : in decreasing order of importance these are the Gezira scheme (Gezira state), several areas in the Dongola region (Northern state), in the River Nile state, White Nile state and the irrigation scheme of Halfa el Jadida in Kassala (along the Atbara River).

Given the continuing incentives to wheat production (both high market prices and Government incentives), wheat areas continue to expand : the Halfa-el-Jadida scheme increased area planted from 5,000 to 33,000fd, while a number of new regions are now planting wheat – in Sennar state, in the Suki irrigation scheme (Sennar state as well) and in Khartoum state. Areas are so far small (22,000fd in total) but are expected to increase in the current climate. In the large Gezira scheme, the area cultivated under wheat has increased four fold relative to the beginning of this decade, with most of the increase coming in the past three years – 150,000fd in 2005/06, 300,000fd in 2006/07 and 420,000fd this season. The increase in area relative to last year is of 40%.

In the season of 2007-2008, most factors were favourable to wheat production – temperature patterns during the development period and availability of inputs (fuel, seeds, fertilizer). In terms of assessment of the national production, the FAO-implemented, EU funded SIFSIA project supported field campaigns of area and yield measurement (crop-cutting campaigns) for the Winter wheat crop (and also the localized winter crop of sorghum and millet in Gash and Tokar), which had last taken place in 2003.

The field campaigns obtained area estimates for Northern and River Nile states only, the remaining regions relying on figures supplied by the state’s MoAs and the Gezira Scheme management. For yield, the campaigns covered the major wheat producing regions with the exception of the Gezira Scheme, where estimates are the responsibility of its management, and the areas in Sennar and Khartoum state which make small contributions. These field campaigns have resulted in more accurate figures for crop area and particularly for crop yield.

The table above presents final results for wheat production in Sudan in 2008. The expected wheat production for Sudan this year is 582,000MT. To this must be added a small amount (estimated at 4,000MT) of “traditional” wheat planted in South and West Darfur (Jbel Marra region) which is consumed locally.

Comparisons with the average of the past 5 years, show this year’s production to be 34% above this average, an increase which is mainly due to the widening in area planted/cultivated rather than productivity (yield).

Seasonal Perspectives

Current La Niña conditions are decaying to neutral and are expected to remain so from mid 2008 to until early 2009.

Rainfall Outlook for July-August-September 2008

July-August-September (JAS) is the crucial period for most crops in Sudan, in particular for the northern regions. Forecasts for JAS rainfall have been prepared in May by a variety of sources. Forecasts made at such long time ranges can provide only general guidance and one can find conflicting information and this is the case for this season.

Fig 5a,b displays forecasts for JAS 2008 rainfall from IRI (International Research Institute) and CPC/NASA (Climate Prediction Centre). As can be seen, they forecast opposite situations, with the former pointing to a wetter than average season and the latter to a drier than average situation. IRI forecasts have performed subjectively well in the past couple of seasons, while CPC’s are judged to perform less satisfactorily.

A forecast from a third source (ECMWF, European Centre for Medium-range Weather Forecasts) is shown in Fig 6. This one agrees with the IRI forecast in that it forecasts a wetter than average JAS period across Sudan (and other areas).

Both the IRI and the ECMWF forecasts display a strong signal for above average precipitation during a period which provides most of the seasonal rainfall in marginal regions of Northern Sudan.

The IRI forecast gives 85% probability of JAS rainfall being on or above average (50% for above), for the Darfur region and 80% (45% for above average) elsewhere in Northern Sudan. For South Sudan, values are slightly lower but still in the same direction. The ECMWF forecast points to more than 90% probability of exceeding the most frequent scenario.

On balance, this Bulletin aligns itself with the scenario of a wetter than average season. If this is verified, it will be the fourth season in a row with generally good rainfall and good agricultural production output.

Forecasts for this period are periodically updated and the predicted situation may still change. In any case, actual crop-related quality of the rainfall season is influenced by a range of other factors such as the timing and distribution of rainfall amounts through the season.