The Indian Ocean Dipole Part II -- The Future Concerns Behind Climate Change and Future Uncertainty for Africa

Last time we have talked about the reason behind extreme events -- the Indian Ocean Dipole (IOD), which contributed to Africa’s precipitation in the eastern region via its positive phase. Under the current situation, the effects of IOD in the future could be worse off due to climate change, especially for Africa. Thus, today I want to continue with this topic and extend our focus to the bigger picture of the future, which is associated with Africa’s resilience to any changes regarding climate change.

 

In a warmer world, there will be more strong positive IODs, such as the one in 2019 that caused devastating floods in east Africa (eg: Mozambique), to bring more extreme events. The climate extremes in 2019 tend to occur more frequently under global warming in the future (Cai et al., 2021). Also, it has been illustrated that pIODs are becoming more common. The occurrence and effects of pIODs are expected to increase with greenhouse warming from the modelling reconstruction and prediction of IODs (Abram, 2020).

 

The reconstruction from 2020 shows that before 1960, the extreme pIODs were rare, followed by the most extreme one on record in 1997, which resulted in the comparable floodings that we have seen in regions of eastern Africa at that time (Abram, 2020). Then, there was an unusual increase in both the number and intensity of pIODs after the 1960s. As demonstrated in figure 1, the pIOD events show a continuing growth trend, with the number of pIODs continuing to rise from 4 events/30 yrs in 1960 to 8 events/30yrs in 2020, and they have exceeded the number of negative IOD events in 2010. This frequency is predicted to continue in the future (2020 to 2080), reaching a peak at over 12 events/30yrs in 2080. At the same time, the pIODs are become more variable in recent years, with the IOD index exceeding over 0.5 °C and peaked at 2 °C for this decade (figure 2). This is further supported by the research evidence from another modelling by scientists in 2014, which claimed that increasing CO2 emissions will contribute to more frequent extreme pIODs for this century, which would shorten the period between two events from every 17.3 years to every 6.3 years.

Figure 1 The number of Indian Ocean Dipole events (per 30 years) based on climate modelling.

 

Figure 2 The IOD index that is used to track the variability of the IOD in the past and future.

 

These facts are undoubtedly associated with the accelerated warming of the western Indian Ocean, which is particularly favoured by human activity. The situation is becoming more tricky under the current situation. It is indicated that the uncontrolled warming during the 21st century could still triple the frequency of extreme pIODs, despite they are supposed to be stabilized at double that of pre-industrial periods due to the aim of limiting the global temperature increase to 1.5 °C from the Paris Agreement (Abram, 2020). Therefore, the affected countries in eastern Africa, such as Mozambique, Uganda, and South Sudan, have experienced much more heavy rainfall and frequent flooding relating to these events, and have suffered from the upcoming damages on crops, infrastructure and human lives. Almost 300 people have died and 2.8 million people have been affected by the events according to the UN (OCHA, 2019).

 

Delay of IOD event

 

Normally the IOD event ends at the start of the monsoon season. However, this ending period had been delayed. According to Dr Watkins, “Normally a period would end at the start of December as the monsoon moves into the southern hemisphere”, but now it's moving quite slowly towards the southern hemisphere, and we are still waiting to see its further movement. He predicted that the event may end one month later than the original. As a result, the negative effects from pIOD, such as the rising temperature, will stay until January. Figure 3 shows this fact by illustrating the trend of monthly sea surface temperature anomalies for IOD regions, it can be seen that after the IOD index was reached its highest due to the pIOD, there is still a long way to go for temperatures to get below the pIOD threshold. Therefore, the affected regions in Africa could suffer from extreme events in a longer period, and may take a longer time to recover from the associated damage. This further increases its vulnerability to climate change.

 

 

Figure 3 Monthly sea surface temperature anomalies for IOD region (source: BOM)