East African Drought – why we should be bothered

The recent news reports from East Africa show tragic and depressingly familiar images of desperate families arriving at UN food stations having not eaten for many days. In this case, the area most severely affected comprises includes southern Somalia, south east Ethiopia and northern Kenya (Figure 1).

Figure 1. Map of East Africa

Although it is easy to become desensitised to such images, it is worth emphasising that this has the makings of a terrible catastrophe on the scale of the 1984 famine in Ethiopia.  The reasons are partly meteorological and partly non-meteorological.

Figure 2. Mean March-May rainfall (2000 - 2009)

From a meteorological point of view, this is a dry area with less rain than at similar latitudes further west. The main rainy seasons, associated with the progression of the Inter-tropical Convergence Zone (ITCZ), occur in Spring and Autumn. Figure 2 shows the average  March to May rainfall total for the years 2000 – 2009 obtained from TAMSAT satellite-based rainfall estimates. The difference between the current year and this average is shown in Figure 3. The area of East Africa shaded brown in Figure 3 has had about 30% of normal rainfall.  The severity of the drought is exacerbated by the fact that this is the 3rd season in row with inadequate rains. For a large fraction of the population  food reserves have already been used up and there is nothing left to tide them through the current period. What makes the situation potentially catastrophic is that we are now entering the dry season. No rain is expected until October and no crops will be harvested till the end of the year.

From a non-meteorological perspective, lack of rainfall is not a problem if you can import food from elsewhere. Saudi Arabia and Israel are examples of countries with inadequate rainfall for feeding their respective populations. However, in both cases they are rich enough to import food to cover any shortfall. This is not the case in the Horn of Africa. In particular, Somalia is virtually ungoverned and infrastructure is non-existent. This means that transport of food even from within the region is practically impossible. Given that such food as is available within the markets is prohibitively expensive, the majority of the population  has little choice but to rely on rain-fed crops and livestock. When that fails, their only recourse is international aid.

For meteorologists, two questions spring to mind: why has the drought occurred? And could better warnings have been given?

Rainfall climate in the Horn of Africa is complex. Rainfall is primarily determined by the seasonality of the ITCZ modulated by the influence of other factors including El Nino/La Nina, the Indian Ocean sea surface temperature,  the location and strength of the easterly jets and low level monsoon winds. Dynamical models do not do a good job in predicting rainfall in this area and  statistical models based on correlations with sea surface temperature are more reliable. The Greater Horn of Africa Climate Outlook Forum (GHACOF) is a body composed mainly of scientists drawn from the East African national meteorological services (NMSs) whose task it is to provide a forecast for each rainy season. The forecasts are based on an assessment of a number of predictive models guided by local knowledge. The outcome is a tercile probability map with a probabilistic assessment of “above-normal”, “normal” and “below normal” rain. As in this country, an NMS which gives an inaccurate forecast is not viewed kindly by the public, therefore forecasts tend to err on the side of caution. The forecast given in February for the March -May season  (Figure 4) shows a slightly enhanced probability of a dry season but does not suggest anything like the scale of the drought which has occurred.

GHACOF seasonal forecast made Feb 2011

The other question of concern is whether the most recent failed seasons are part of a trend or natural variation of a stable climate. Here again, the complexity of the climate militates against easy answers. The 4th IPCC report suggests a tendency towards increased rainfall in East Africa in future climate scenarios. On the other hand some recent research (Williams and Funk, 2011) argues that warming of the Indian Ocean may be suppressing March-May rainfall on a long term basis. Developing a better understanding of the climate in this region is quite literally a matter of life and death.

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