Low rainfall and high evapotranspiration would not have led to droughts without global warming, study shows
Photo: iStock Long-term droughts such as the one going on in the Horn of Africa region, especially in its southern parts, have been made 100 times more likely by climate change, according to a report by the World Weather Attribution (WWA) group.
The WWA is a collaboration of climate scientists from around the world who work on attributing extreme weather events such as droughts, heatwaves, extreme rainfall, floods and cold spells to the effects of anthropogenic greenhouse gas emissions-induced global warming and resultant climate change.
Such droughts are a result of a combination of impacts from low rainfall and high temperatures and can be categorised as meteorological (lack of rainfall) as well as agricultural (decrease in soil moisture content, increase in transpiration from plants and reduction in crop yields).
The southern parts of the Horn of Africa, which includes southern Somalia, southern Ethiopia and eastern Kenya, witnessed below-normal rainfall from 2020-2022, the study found.
There are two kinds of rainfall periods in this region known as the short rains, which occur from October to December, and long rains, which occur from March to May.
While scientists observed below-normal short rains in 2020, 2021 and 2022, they observed below-normal long rains in 2021 and 2022.
The scientists analysed all rainfall events that occurred in the region from January 2021-December 2022 and also the short rains and long rains periods separately.
They found that below-normal rainfall in the long rains period occurred once in a decade, while the same for short rains period occurred was once in five years.
They also noticed a trend of low rainfall during the long rains period, while an opposite trend of more rainfall was noticed for the short rains period.
For the 24-month period, there was only a 5 per cent chance of below-normal rainfall every year without a major trend.
To quantify the contribution of climate change in the above occurrences, they used climate models and looked for similar less rainfall events in the model data.
They found that the actual observations of low rainfall events matched the model data and that low rainfall during the long rains period has been made twice as likely by human-induced climate change.
The fact that during this entire period a La Niña event was also occurring in the equatorial Pacific Ocean made the trend of increased rainfall during the short rains periods attributable to climate change.
During La Niña, the cooler-than-normal phase of the El Niño Southern Oscillation phenomenon, the drought occurrence is enhanced in the Horn of Africa region.
To understand the contribution of climate change in the occurrence of agricultural drought, which accompanied the low rainfall periods in the region, the scientists also looked at how evapotranspiration changed during the 24 month period.
During an agricultural drought, the decreased rainfall reduces the moisture content of the soil that is essential for the growth and productivity of crops. High temperatures increase the chances of this happening as they increase the evapotranspiration from plants.
Evapotranspiration is the process through which plants lose water to the atmosphere to maintain their water content and temperature.
The authors of the report found that in a world without the current global warming of 1.2 degrees Celsius, the combined impact of low rainfall and high evapotranspiration would not have led to drought at all.
But in a warmed up world grappling with climate change, the events lead to an exceptional drought.
“Climate change has made events like the current drought much stronger and more likely; a conservative estimate is that such droughts have become about 100 times more likely,” the scientists noted in the report.
The three-year drought in the region has had wide-ranging impacts on people’s food and water security, their livelihoods and health. Around four million people in the region are suffering from acute food insecurity.
This is mainly because most of the people in the region are still dependent on rain-fed agriculture, agro-pastoralism and pastoralism which are extremely vulnerable to drought conditions.
Prolonged drought conditions are not the only factors which are caging the region’s people in a cycle of poverty that would be difficult to get out of.
“State fragility and conflict, as well as the length of the drought played a significant role in worsening outcomes, especially for people in Somalia,” the study showed.
“Further, the severity of impacts linked to the long duration of the drought also raises serious questions about the length of droughts that government drought management systems and the international aid infrastructure should be prepared to handle in the future,” the researchers observed.
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