The 1994 Sahelian Rainy Season-- The Wettest Since 1964

The 1994 rainy season was the wettest since 1964 across the Sahel, based on preliminary May through September data (Fig. 1). Using the 1951-80 period as the baseline "normal," 1994 is only the second year since 1967 to record above-normal rainfall for the season. Although the heavy rains brought damaging floods to many areas, the longer-term impacts are primarily beneficial, with water supplies ample and agricultural prospects among the best in years.


One factor contributing to abundant rainfall during 1994 was the northward displacement of the Intertropical Discontinuity (ITD), which marks the northern boundary of maritime air. This year's migration of the ITD, which is generally equivalent to the ITCZ, is shown in Figure 2. Northward anomalies equate to enhanced rainfall in the Sahel. Through June, its northward advance (solid line) was close to the 15-year (1979-93) normal (dashed line), but from July into October, the humid air was north of normal. As a consequence, much of the Sahel and the southern Sahara Desert saw the heaviest rains in years.

The June-September average latitude of the ITD correlates historically with both rainfall and agricultural production in the Sahel region of Africa. Figure 3 shows that the 1994 ITD latitude was the highest across West Africa since records began in 1979.

Data across eastern Africa is more limited, but also shows that the conditions were favorable for heavy rainfall in East Africa during 1994, including Sudan, Ethiopia, and Eritrea. Figure 4 indicates that the ITD east of 20øE was the farthest north of the last six seasons.

Rainfall Totals

The total rainfall and percent of normal rainfall maps for the season (Fig. 5) illustrate the large areal extent of the heavy rains across Africa, with cumulative totals exceeding 120 percent (%) of the 1961-90 mean across large sections of Senegal, Mauritania, and Mali, as well as most of Niger's crop area, southwestern Chad, northern Sudan, and eastern Ethiopia. Over 1000 mm fell on the Ethiopian highlands and most areas from 11øN southward to the Equator, except from central and western Burkina Faso southward across central and eastern Cote d'Ivoire and western and southern Ghana.

Damage frequently resulted from heavy rains and was especially pronounced in Sudan, Ethiopia, and Niger, according to press reports. In August, the Niger River Basin Authority reported that the Niger River contained its highest volume since 1950. During the five-month period in Niger alone, more than three dozen individuals were killed by flooding, over 127, 000 people were rendered homeless, and approximately 3000 sq. km. of crops were destroyed, according to government officials appealing for international aid.

There were few areas with below-normal rainfall. The most significant dryness stretched along the Gulf of Guinea coast from Cote d'Ivoire eastward to the immediate coast of Togo and Benin. Less than 80% of normal seasonal rains fell from extreme eastern Liberia eastward across central and southern sections of Cote d'Ivoire, Ghana, Togo, and Benin and only about half of normal was measured along the extreme southern tier of Cote d'Ivoire.

Monthly Highlights

The season began with fears of a developing famine across East Africa, with weather problems only one among other contributing factors. Below-normal rainfall during May ensured a poor minor season ("belg") crop for much of Ethiopia. There were also food supply concerns in Kenya, Sudan, Somalia, and Eritrea due to earlier poor harvests.

June brought near or above normal rains to much of the Sahel as most areas south of 12øN recorded over 200 mm of rain, with the exception of the Gulf of Guinea coastline from extreme eastern Guinea eastward to Benin. Less than half of normal rain fell on these areas, as well as parts of Chad and the Ethiopian lowlands. Other areas, however, received ample rainfall, with well above-normal amounts in northern Nigeria and central and southern Sudan. Plentiful rains also alleviated food shortage concerns in Somalia and Kenya.

In July, the main rainy season got under way in Ethiopia, but its delay in some central and eastern areas posed a potential problem for the autumn harvests. When the rains arrived, however, they were impressive. Media reports indicated that flooding forced 60,000 people from their homes near the Red Sea in Ethiopia and Djibouti. Farther west, abundant rains fell on much of the Sahel and sub-Saharan Africa, with significant showers reaching exceptionally far north (past 20øN) in both Mali and Sudan. Well above-normal July rains also soaked southeastern Niger and parts of central and northern Chad. Farther south, less than 25 mm fell on most areas from eastern Liberia to southwestern Ghana.

August was also unusually wet, with heavy rains (100-400 mm) drenching most areas from Senegal and southern Mali eastward to western Sudan as well as central and northwestern Ethiopia, northern Cameroon, and northwestern Zaire. Totals were well above normal (>150%) in a swath from north-central Mauritania southeastward to central Chad. Flooding marooned 30,000 people in the Ethiopian highlands early in the month, according to press reports. Flooding even swept into some of the drought-affected areas of southern Ethiopia during the last half of August, destroying lives and property, and reportedly left 30,000 people homeless in Niger.

The widespread wetness continued through September, with exceptionally heavy rains (100-400 mm) falling from central Senegal southward through Liberia and eastward to central Ethiopia. Convective complexes continued to track unusually far north into typically dry areas of Mali and Niger.

October saw drier conditions finally beginning to cover the Sahel, but occasional heavy rains still fell unseasonably far north, with new October records established in southeastern Mauritania. Flood reports continued, including one event near Khartoum, Sudan. Farther south, above-normal rains erased lingering dryness in Cote d'Ivoire and along the Guinea coast.


Despite localized crop damage from excessive rainfall and flooding, production prospects for the crops currently being harvested are mainly favorable. There are some areas of concern because of either a late start to the rainy season (Senegal's northern groundnut basin, eastern Ethiopian crop areas) or dry periods within the growing season (central and southwestern Burkina Faso, western Mali, western Niger south of the Mali border), but the abundant moisture in most areas should lead to a positive outcome across the region from Mauritania eastward to Sudan and Eritrea.

Contributing Factors

The anomalous northward extension of the ITD during 1994 was a major factor contributing to the wet conditions across the Sahel/Sudan zones of Africa and the dryness farther south along the Gulf of Guinea coast. African tropical waves tend to be more active in the Sahel when the ITD is farther north, and the squall lines associated with the tropical waves are believed to be responsible for about 80% of the total rainfall during the rainy season. In 1994, the relatively high frequency of the waves and the associated squall lines may have been associated with a well-established African Easterly Jet (AEJ) at 700 mb and a strong Tropical Easterly Jet at 200 mb. The location and intensity of the subtropical high pressure systems over the oceans surrounding Africa, along with the location and intensity of anomalous sea surface temperatures, also influence Sahelian precipitation. During the summer of 1994, the subtropical high pressure systems tended to be north of normal, both at the surface and aloft. This contributed to the hot summer in Europe and likely to the northward extension of the rains in Africa. In addition, during June and July, there were unusually low sea surface temperatures in the Gulf of Guinea near the equator. Historical studies have shown a correlation between cool water in this region and unusually wet seasons in the Sahel. The effects of large-scale circulation features and sea surface temperatures on the 1994 season are still being investigated.

Comments on the Long-term Outlook

There is no evidence that the 1994 season is the start of a trend toward the wetter Sahelian climate of the 1950s and early 1960s (Fig. 1). The long-term climate records of rainfall , lake levels, and stream flow suggest that the extended period of dryness which began in the late 1960s and has continued into the early 1990s should eventually be followed by a period of increased rainfall in the Sahel, but there is no reason to believe that this change is imminent. Though the outlook for next year is also not known, there are a few indicators that raise some hope for normal or better rainfall, at least compared with the past 25 years or so. Research by Chris Landsea, Bill Gray, and John Knaff of Colorado State University has shown that above-normal rainfall over the Gulf of Guinea countries during the August-November period correlates with favorable rainfall the following summer in the Sahel. The October-early November period is especially significant. This year, so far, rainfall has been well above-normal in the Gulf countries during October. Some other indicators, such as stratospheric winds, also look favorable. Nevertheless, given the mixed record of past attempts at seasonal forecasts for the Sahel region, extrapolating this year's rainfall into the future would be very speculative.