The influence of ENSO and IOD on water trends in Africa

Following the study cases I explored in the previous blog posts, I will discuss the influence of climate patterns on extreme weather events in Africa. The two events worth discussing are El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). ENSO has an influence around the Tropical Ocean, where El Niño tends to increase precipitation from warming the ocean surface, with La Nina cooling down the ocean surface and decreasing. Even though it is not geographically located next to Africa, previous studies have suggested that ENSO has influenced the amount of heavy rainfall in 1970-2000 in Eastern Africa, and it is generally considered to be a driver behind drought in Southern Africa through the inter-annual climate variability created in this region. Furthermore, ENSO has an influence on the Indian Ocean Dipole, directly involving Eastern Africa and surrounding areas of the Indian Ocean.

Indian Ocean Dipole can be defined as the difference in sea surface temperature between two regions within the Indian Ocean. A positive IOD phase, being cooler water temperature in the East Indian Ocean and warm temperature in the West Indian Ocean, is most relevant to the study cases discussed, as it tends to increase heavy rainfalls and floodings in Eastern Africa. (Figure 1) Inversely, a negative IOD tends to increase rainfall in parts of Australia, and bringing below-average temperatures from changing wind patterns in most parts of Africa. It is important to note that the intensity of the IOD has been significantly higher as climate change intensifies, observable in the 2019 positive IOD phase, which was the strongest in the last 6 decades and is gradually intensifying. Furthermore, it is expected that extreme IOD events, such as floods, and droughts, will happen every 6 years in the 21^st century, being three times more than in the 20^th century.

 

 

 

Figure 1: Indian Ocean Dipole Positive Phase

The influence of these climate patterns on precipitation is heavily argued in various research. For example, a statistical analysis performed in Nigeria between seasonal rainfall of different regions and IOD Mode Index suggested that IOD events increase and decrease precipitation in Nigeria, despite being non-contiguous geographic regions. (Ezedigboh et al., 2018) For the case of Madagascar, IOD events tend to increase rainfall in the northwestern and southern regions. (Randriatsa et al., 2022) This would coincide with the increased rainfall causing severe landslides in Antananarivo and frequently worsening cyclones in Eastern Madagascar. The increasing influences of both ENSO and IOD due to environmental change emphasizes the need to predict the impacts of these environmental variables on rainfall. Endris et al.’s (2019) study on future rainfall trends associated with ENSO/IOD changes found that there would be an increase in rainfall anomalies in Eastern and Southern Africa, as well as an increased teleconnection between rainfall changes from ENSO/IOD in the remaining regions of Africa.