Science

Climate change predicted to intensify East Africa’s rainy season

Source: John Wambugu (Flickr)
New research suggests climate change will lead to longer rainy seasons in East Africa, resulting in floods followed by droughts, and harder conditions for farming.

By Rowenna Hoskins | Science Editor

According to new research, climate change is going to affect East Africa with much wetter conditions than scientists had previously thought.

The University of Texas at Austin, who published the study in Climate Dynamics, have found scientific data that contradicts predictions of a much drier climate made earlier in the century. The new data shows that East Africa’s rainy season called the ‘short rains’ is going to almost double by the end of the century and the pattern is already observable in recent years.

Africa has two rainy seasons the ‘short rainy season’ and the ‘long rainy season,’ both of which have different sensitivities to greenhouse gases.  The study contains 30-kilometre resolution simulations which measure the amount of precipitation that falls within an area.

While the ‘short rains’ are very sensitive to greenhouse gases, and are set to increase dramatically, the ‘long rains’ are less sensitive. They are projected to remain relatively stable, meaning that East Africa will experience more rain for a longer period of time.

“Our paper shows that the short rains will continue to increase – in fact, flooding and locust infestations are already occurring – and there is no dying trend for the long rains,”

says Kerry Cook, a professor at Jackson School of Geoscience department of Geological science.

The reason for this difference in sensitivities is down to the way that precipitation is formed in the different rainy seasons.

Precipitation difference occurs because the transportation of water vapour by atmospheric circulation and the distribution of rain are sensitive to differences between ocean and land temperatures.

Climate change is causing the heating up of the planet; greenhouse gases trap the heat from the sun within the atmosphere. This causes the land and the sea to heat up, but due to different heat capacities, they do so at different rates. Oceans warm and cool slower than land, as it has the highest heat capacity of all common Earth materials, making it a great thermal buffer. Unfortunately, this means that the difference between the temperature of land and the sea is increasing which causes more moisture to evaporate from the oceans which in turn causes more extreme weather conditions.

When short rains in Africa develop, typically peaking in November, the southern hemisphere circulation is in a summer pattern. This means there is a high pressure over the ocean and low pressure over the land in the subtropics. The differing pressure sets up a circulation patterns that funnels more moisture over East Africa.

Contrastingly, long rains which peak in March to May, are less sensitive as they peak near the northern hemisphere’s spring equinox. This creates low pressures that are centred over the equator, meaning that the rains are not largely affected by the difference in heat capacity between the land and the sea.

The simulation that predicts this pattern has been achieved at the highest resolution currently possible, 26 kilometres above what was possible a year ago. It involves complex analysis of East African topography and represent a much more accurate measurement of seasonality and precipitation than previous global models.

The simulation’s projected rainfall patterns up to 2050 are consistent with current observed rain amounts and seasonality. While the long rains will not change, the short rains will increase in November. They are predicted to increase by a third by 2050 are set to double by 2100.

Despite only contributing 4% of greenhouse gases, Africa will be the hardest hit by climate change. 17% of the worlds population that live in Africa will suffer dire consequences as a result of pollution that they did not largely contribute to.

Although there will be more rain in the short rainy season, this is not good news for Africa. Climate change will mean than Africa will experience long droughts and then equally long rainy periods. This means that there will be more floods, hurricanes, and rainfall.

Agriculture will be severely threatened as it will be both too hot and too wet throughout the year, with no grace period within which farmers can grow healthy and successful crops with the addition to locust infestations. It will become impossible to grow food to feed the 1.3 billion people who live there, and thus there will be an increase in migration, as well as an increase in conflict for resources.

“This research will allow people to plan ahead in East Africa,” said Cook. “But future work will need to see how additional rainfall will be delivered because, if it is as intense as the current observations and continues to impact agriculture, developing infrastructure will be important.”

Climate change is a matter of social justice, the worst affected are the countries who have had the least impact on the climate crisis. This statement is highlighted by the ominous predictions for Africa’s raining season.

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