Special Report on Floods in Southern Africa
REGIONAL FOOD SECURITY PROGRAM - GROWING SEASON STATUS - 1999/2000 - Issue 2 - February 2000
Released 9 March 2000
A tropical depression and Cyclone Eline ravage large parts of the four southern African states of Mozambique, South Africa, Botswana and Zimbabwe during the month of February. High winds, torrential rains, and severe flooding has left a trail of destruction and heavy loss of life.
- Large areas of potentially productive agricultural land has been flooded, together with livestock and farming implements.
- The food security prospects at both national and regional level are still uncertain.
- Considering the present accumulated rainfall and hydrological situation in the six major river catchment areas in southern Africa, the situation is not likely to improve in the near future.
- Mozambique is the worst affected country, where up to 400 people reported dead and about a million displaced.
- An international appeal for assistance has been launched.
The Regional Remote Sensing Unit (RRSU) has prepared this Special Report on the recent floods in Southern Africa, covering the period February 1-29, 2000. This Special Report serves as the monthly Growing Season Status Report for February 2000.
The analysis presented in this bulletin is based on Meteosat derived Cold Cloud Duration (CCD) images, which are received through the RRSU managed PDUS receiving station which is located at the Zimbabwe Meteorological Department in Harare, Zimbabwe (ZMD-Harare). The RRSU acknowledges the role of EUMETSAT in making the Meteosat data accessible through the ZMD-Harare.
The RRSU has also provided regular updates on the progress of the 1999/2000 rainy season through the Agromet Update, which is being distributed by the SADC Regional Early Warning Unit and the FANR Web-site.
Cyclone Eline hit the southern African region on Monday 21 February 2000 and caused heavy and excessive rains in the already waterlogged lower and upper coastal regions of Mozambique. The cyclone was preceded by a tropical storm during the first half of February. The accumulated rainfall situation will have a great impact on the region for the next few months and will be a threat to the food security situation in the region which will last well in to the next growing season. This report summarises the rainfall situation during February 2000 and will show the impact on the six major river catchment areas in the region.
Analysis in this bulletin is primarily an interpretation of satellite imagery, with incorporation of appropriate ground information. Ground data and interpretation are provided by the collaborating national meteorological services and national early warning units of the SADC Member States and are summarised in the situation map on the last page.
The focus of this bulletin is primarily at the regional level. At the moment the RRSU satellite image archive does not include the Democratic Republic of Congo, the Seychelles and Mauritius. These countries will be included in future bulletins. However, any information available has been included in this report. For more detailed sub-national analysis, readers should consult the national meteorological agencies and food security early warning units.
Special Report on Floods in Southern Africa
This Report is being produced at a time when large parts of the southern Africa region are in the middle of an unprecedented disaster in term of human suffering, loss of life and severe destruction of the basic infrastructures due to the effects of two tropical storms that hit the region in February
Nature of cyclones in Southern Africa
While cyclones are a feature of the rainy season in southern Africa, with the cyclone activity expected between November and March, very few of these cyclones cross the land with such devastating effects. The last such cyclone to cross onto the subcontinent mainland was "Bonita" in 1996, but only brought heavy rains and minimal flooding. The double effects of the tropical depression that affected parts of the four southern African countries (Mozambique, Zimbabwe, South Africa, and Botswana during the first half of February, and quickly followed by cyclone Eline during the second half of the month resulted in unprecedented flooding across the region. Cyclone Eline pounded a region that was already soaked with the heavy rains of the tropical depression the week before.
River catchment areas
The flooded areas in Mozambique consist of the floodplains and lowlands of the major rivers in this region, the Limpopo, Save, Pungoe, Zambezi, Incomati, and Buzi. Both the tropical depression and the cyclone saturated the catchment areas of the above-mentioned rivers, with some areas receiving half to three quarters of their average annual rainfall during this period. The subsequent high river flows emanating from these catchment areas caused severe floods in downstream areas.
Cyclones and tropical depressions
The high frequency of tropical depressions in the Mozambique Channel, and the several cyclones that came into the area in January and February (note that Eline was the 5th cyclone into the region this season), also had the effect of keeping the Inter Tropical Convergence Zone (ITCZ) anchored in the region with heavy convective activity linking the low pressure centre in the Caprivi area with the one in the Mozambique Channel. The net effect has been heavy rains associated with the ITCZ falling into the Zambezi river basin during the past few weeks.
The rivers and dams in the Zambezi basin have also been flooding in recent weeks, culminating in the necessity to open the floodgates on the Kariba Dam in late February. The release of floodwaters from the Kariba Dam, and possibly from Kabora Bassa downstream at a later stage, is likely to add to the flooding that is occurring in the floodplains of the Zambezi downstream.
Cyclones are spawned in the central and eastern Indian Ocean, 5°-10° south of the Equator, when sea surface temperatures of 27°C or warmer enable the formation of a low pressure area that then develops into a tropical depression. About half a dozen or so cyclones are formed in this way every year. Once formed, and conditions continuing favourable, the depression moves westwards towards Madagascar. The movement and intensity of the depression depends on the availability of warm moist air along its path. When its winds reach a speed of 115 km per hour or more, the tropical depression becomes a cyclone. On average the cyclones that reach the western Indian Ocean normally reach Madagascar, and often the Mozambique Channel, but then curl away to the southeast into the Indian Ocean. Because a cyclone needs huge areas of warm moist air to sustain its strength, it quickly loses its strength once it hits the land due to ground friction and loss of the source of the energy.
However, Cyclone Eline was an exception as it became rejuvenated over the land.
Figure 1. The major river catchment areas that are responsible for the continuing flooding situation in Mozambique.
In figure 1 the major river catchment areas responsible for the flooding situation in Mozambique, Zimbabwe, South Africa and Botswana are shown. Also indicated in this map are the lower and upper coastal areas in Mozambique which have been flooded as a result of the heavy rainfall. These coastal areas will be further affected as rains continue not only in the catchment areas, but also in the flood plains of Mozambique.
Progress of the season until late-January
The season had so far been characterised by a late start of seasonal rains in parts of South Africa, Lesotho, Swaziland and southern Mozambique. Normal rains started across the region in November, into December. A prolonged dry spell in December affected parts of central and southern Mozambique, Zimbabwe, southern-central and eastern Zambia, southern and central Malawi, and caused some concern in the affected countries. However, the dry spell dissipated at the beginning of January and favourable rains have been received in most parts of the region so far.
Although the Climate Outlook Forum (SARCOF) had predicted normal to above normal conditions across most parts of the region, the high frequency of tropical storms and possible flooding was not foreseen. To date, seven storms, some at cyclone strength, have been observed moving into the western Indian Ocean and the Mozambique Channel.
Two of these are responsible for the flooding and extensive damage that has occurred in Mozambique, South Africa, Zimbabwe and Botswana in February 2000.
Tropical storm in early February
Progression of the first tropical depression over Southern Africa. The red and orange colours show the position of the depression. The black shaded areas are the 6 major catchment areas in the region.
The first tropical depression in the period from 1 to 15 February 2000 caused severe flooding in Mozambique, Zimbabwe, South Africa and Botswana. High and excessive rainfall was recorded in the southern half of the marked area, which are the Limpopo and Buzi catchment areas.
The tropical storms of early February were followed by Cyclone Eline. This cyclone started its move into Southern Africa on the 21st of February (see figure 3). After this it continued its destructive route into the region causing excessive rainfall in the Pungoe, Buzi, Save and Limpopo catchment areas.
Figure 3. Satellite image showing the position of Cyclone Eline on Monday 21 February 2000
in relation to the major catchment areas.
Again the Limpopo catchment received heavy rains, but also the Save and Pungoe catchment areas received excessive rains. The associated rains in the other areas in the region were also considerable high.
Time Series for the major river catchment areas
One of the RRSU products derived from satellite information are data extracts from Cold Cloud Duration (CCD) imagery, which are presented as cumulative values compared with an 11-year (1988-1999) average for specified sub-regions of SADC. These sub-regions can be administrative boundaries, watersheds, catchment areas, or agricultural areas. Suggestions for new areas to allow a more focussed monitoring are welcome. CCD curves are here presented for the six major river catchment areas. The catchment areas have been composed from the ALCOM watershed map of southern Africa. All satellite information used for the CCD curves has been received and processed by the RRSU.
Flood Plains in Mozambique
The two worst affected areas in Mozambique are the low-level coastal flood plains (see figure 1: Lower and Upper coastal areas). In figure 5a and 5b there are two graphs with the cumulative rainfall situation in both areas. It can be seen that until late January the rainfall season was developing favourably around the normal pattern. During February a sharp increase in rainfall was observed and the present cumulated rainfall situation for this season is well above normal in both areas.
While the curves for the Zambezi catchment area and the northern and southern Kariba catchment areas seem to indicate that the situation is near to normal, recent heavy rains in these catchment areas, and the subsequent opening of the Kariba dam, are likely to cause flooding in downstream areas.
All graphs provide evidence that, considering the present accumulated rainfall and hydrological situation in the six major river catchment areas in Southern Africa, the situation is not likely to improve within the near future. It will take considerable time before the water will recede from the flooded areas in Mozambique, Zimbabwe and South Africa.