Geneva — Hundreds of thousands of people in East Africa are affected by heavy rains and floods linked to record-breaking temperature changes in the Indian Ocean.
The western Indian Ocean has been about two degrees warmer this month than the eastern Indian Ocean. As a result, higher evaporation off the African coastline is being dumped inland as rainfall: a simplified description of 2019's positive Indian Ocean Dipole (IOD) episode.
This year, the IOD is "enormous", according to climate scientist Saji Hameed, who studies the phenomenon at the University of Aizu, Japan.
Hameed told The New Humanitarian that equatorial East Africa is "very, very likely" to be unusually wet from October to December, adding: "November is the most dangerous month as far as IOD impacts are concerned, as enhanced rains reach far into highlands and the watersheds of several rivers."
In an email response to questions, the Kenya-based regional Intergovernmental Authority on Development Climate Prediction and Applications Centre (ICPAC) confirmed the pattern.
While cautious not to attribute complex systems to a single cause, ICPAC climate modelling expert Zewdu Segele told TNH that "high rainfall events associated with flooding in [parts] of Ethiopia, Somalia, South Sudan, and Kenya are likely related to this positive IOD state."
Rainfall in the first part of October has already been "much wetter than average", according to monitoring by the multi-agency Greater Horn of Africa Climate Outlook Forum.
Segele said ICPAC predicts mixed blessings: some areas will have better harvests and grazing for animals. Others will suffer flash flooding - too much rain could spoil crops as they mature, and trigger livestock disease.
Hameed pointed to 2006 for some clues of what to expect. That year, East Africa saw heavy rains, floods, and extensive health issues. The wet conditions contributed to an outbreak of Rift Valley Fever, a disease that affects animals and humans. By March 2007, it had killed 155 Kenyans. In Somalia, 450,000 people were displaced by the 2006 floods and roads to the Dadaab refugee complex in Kenya were cut off.
This year's sea temperature difference is bigger than in 2006, and the biggest since the Australian Bureau of Meteorology set up weekly tracking in 2001. Australia's weather is also influenced by the IOD: a positive IOD is linked to a wetter East Africa, but drought in Australia.
This year's positive IOD may be may be the biggest since the 1980s, according to longer-range satellite-based estimates of sea temperatures, Hameed said.
According to the World Meteorological Organisation, the current period is "neutral" for the El Niño phenomenon, a better-known global climatic system influenced by temperatures in the Pacific Ocean. The relationships between the two - and their possible future effects on climate change and patterns of rainfall - remain the subject of research. The IOD itself was only identified in 1999 by researchers in Japan.
While longer-term predictions are therefore hard to make with much accuracy, here's the situation right now in East Africa:
The UN reported on 21 October that 600,000 to 800,000 people are affected by heavier-than-usual seasonal flooding in South Sudan.
While floods can be good news to refill groundwater and revive agriculture and fishing, the UN and other aid groups are assessing emergency needs in at least 10 locations.
Médecins Sans Frontières had to evacuate a hospital in another South Sudan town, Pibor, due to floods. The medical NGO said acute watery diarrhoea, cholera, malaria, and respiratory tract infections would likely rise as floods spread. The group also expects to treat more cases of snakebite as the reptiles seek refuge on dry land along with displaced people.
Floods around the South Sudanese town of Maban, fed by rivers from highland Ethiopia, have affected 200,000 people. The UN's refugee agency, UNHCR, reports that although floods at this time of year in the region are normal, the scale of Maban's this year is "unprecedented".
Local rainfall and increased river flow from Ethiopia makes flooding in October "highly likely" in many southern areas of Somalia, according to a report from the Food and Agriculture Organisation.
"We are seeing localised flooding and that is likely to increase," said Justin Brady, head of the UN's emergency aid coordination office, OCHA, in Somalia.
US-funded famine watchdog FEWS NET reported that higher rainfall in Somalia "would be a welcome relief from several consecutive seasons of agricultural and hydrological drought."
Brady said a poor previous rainy season had contributed to the worst harvest on record and hoped good short rains in the October-December period could see a "rebound in agricultural production."
In 2016-17, the reverse effect, a "negative" IOD, was linked to drought in Somalia and southern Ethiopia. "A lot is made of El Niño, but the dipole is what has the most impact in Somalia," said Brady.
The Kenya Red Cross Society is positioning supplies, preparing its response for an initial 30,000 affected people, and warning communities at risk. It has carried out some evacuations (including 100 stranded camels) and responses to localised floods already, for example in the northern town of Moyale.
"It is a serious event" and it "may get much worse", Red Cross climate advisor Maurine Ambani told TNH. "Everyone needs to be alert; so getting out the message is important."
Kenya's Meteorological Department provided a forecast in late September for the Kenya Red Cross saying there was a strong likelihood of higher than five-year average rains in most of the country, parts of which, like in Somalia, are recovering from drought.
Ambani said the Red Cross was seeking funding to prepare for various scenarios and called for early humanitarian action based on forecasts to be better funded. Given the inevitable uncertainty, donors should be "ready to take risks using imperfect forecasts", she said.