The Eastern African Paradox

The Eastern African Paradox 

My first associations with Africa and Climate change are often images of severe droughts, water shortages, and floods. Although floods are part of this image, I thought of Africa as getting dryer with just occasional extreme weather events such as heavy precipitation. This course together with my other course, global environmental change, has opened my eyes. I was very surprised when finding out that climate change models project the eastern part of Africa to get wetter, instead of getting a dryer climate.

Droughts are ravaging countries in the East African region as long rains in the wet season failed, bringing, among other humanitarian issues, a food crisis.  Although models predict the region to get wetter, both local weather data and dry streams show otherwise (Del Bello, 2017). This blogpost will consider this contradiction, the so-called Eastern African paradox.

Figure 1: Worldwide precipitation predictionIPCC, 2017

Observations

Lack of sufficient data on precipitation in the whole continent Africa makes it hard to conclude things about annual rainfall in most areas. Besides, the existing data is in many regions often inconsistent and therefore also not useful to draw conclusions (Niang et al., 2014). However, sufficient data in eastern Africa make it possible to draw some conclusions about precipitation trends in eastern Africa over the past century. It is very likely that annual precipitation in eastern Africa has increased. Yet the precipitation in eastern Africa differs a lot both spatially and temporally due to physical processes, thus decreases in precipitation have also been observed (Niang et al., 2014).

• A decrease in rainfall in the last 30 years between March and May/June, the so-called “long rains” (Niang et al., 2014; Rowell et al., 2015). Warming of the Indian Ocean is expected to be the cause of this. As convection and precipitation increases over the tropical Indian Ocean, due to the warming of the ocean, this contributes to both increased subsidence over East Africa and a decrease in precipitation (Niang et al., 2014).
• During the summer months, June until September, a decrease in monsoonal precipitation is observed over the last 60 years. The trends here in the “short rains” or do not have a clear downward trend such as the long rains, but there is more year-to-year variability. This is partly the result of changing sea level pressure gradient between Sudan, the southern coast of the Mediterranean Sea and the Southern Tropical Indian Ocean region (Niang et al., 2014).

Predictions

Models predicting precipitation in eastern Africa imply that there will be more intense wet seasons and less severe droughts in the months October-December and March-May. This prediction contradicts the observed changes that show a decrease in precipitation in the months March until May. It is, thus, expected that there will be a reversal of the trends in precipitation in recent decades. This will be the result of cooling in the eastern equatorial Pacific that will counterbalance the equatorial pacific sea surface temperature warming (Niang et al.,2014). Figure 2 shows the disparity between the predicted increase in East African rainfall and the observed decline (Rowell et al., 2015).

Nevertheless, also in the prediction models there are major regional differences such as predicting droughts in parts of Uganda, Kenya, and South Sudan in August and September because of weakening Indian monsoon and Somali Jet. Therefore, regional-scale atmospheric processes and local-scale factors such as land surface should always be considered and could be of a big influence on climate forecasts.

Figure 2: The Eastern African Paradox

Explanations

There are multiple possible explanations for the paradox. In this paragraph, I will mention some.

1. As I mentioned in the beginning, there is a problem with the data used. Both because of a lack of data and bad quality (Rowell et al. 2015; Niang et al. 2014). Although it seems that there is enough data to conclude things about the eastern region, poor quality data could still have had an effect on the observational data (Rowell et al. 2015).
2. Both past and future trends occur because of natural variability. Evidence suggests that it’s unlikely that natural climate variability is the only driver of the droughts. It is highly possible that another driver, such as aerosol, together with natural variability force the droughts. It might be possible that changing anthropogenic aerosol emissions are the cause of the downward trend of the long rains (Rowell et al. 2015).  
3. Land-use change in the Eastern region, as well as the rest of Africa, could also be the driver for the decline in recent rainfall. Tropical climates can be sensitive to large changes in the land surface. Studies have found a significant sensitivity of rainfall to land-use change in Kenyan with the expansion of agriculture. However, more studies are needed to really conclude if this contributes to the rainfall trends (Rowell et al. 2015).

1   Although the trend is often described as the paradox, it does not have to be a paradox. It could still, be the case that in the long term the eastern African region is getting wetter, but that other drivers bring droughts in the short term (Del Bello,2017).