Southern Africa is slowly plunging into the effects of what could be one of the region’s worst droughts in decades.
In the absence of timely interventions and adequate preparations being immediately implemented, a looming disaster which may equal to or even surpass the impacts of the 1991/1992 southern Africa’s drought of the century is gradually unfolding.
Virtually all available climatic pointers are concurring to that regional effect.
Unless the Almighty God intervenes to reverse these rather loud indicators, this slow onset hazard may lead to severe water and food shortages.
An analysis of the satellite-based rainfall estimates indicates that Western Zambia, Zimbabwe and south of Mozambique hardly received half of their respective rainfall totals since the beginning of the rainfall season.
This is despite the unprecedented scorching heat that is quickly evaporating any little rain that could have fallen and not only enhancing the depletion of available water bodies, but lowering the water tables beyond the majority of the borehole depths.
Even if the region is well past the mid-season, some significant pockets within the region are yet to record the onset of the rainfall season as defined by the SADC Climate Services Centre (CSC).
If this trend persists, the current rainfall season is poised to result in severe long-term environmental, economic and health impact on the population of the region.
Even wild and domestic animals may not be spared from the effects, given that the drought is coming on the backdrop of yet a preceding drought which has taken its toll on 200 elephants in Mana Pools and Hwange National Park in Zimbabwe just before the commencement of the current rainfall season.
The main culprit to these unfolding regional devastating events is attributed to the current occurrence of higher-than-usual temperature differences between the two sides of the Indian Ocean — something meteorologists refer to as the Indian Ocean Dipole (IOD).
The IOD — often called the “Indian Niño” because of its similarity to its Pacific equivalent of El Nino Southern Oscillation (ENSO) — refers to the difference in sea surface temperatures of opposite anomalies over the east and western parts of the tropical Indian Ocean.
The temperatures in the eastern part of the ocean oscillate between warm and cold compared with the western part, cycling through phases referred to as “positive”, “neutral” and “negative”.
The IOD this season is in its positive phase. Relative to ENSO, the IOD is quite a recent phenomenon to climate scientists, having been discovered in 1999 by a group of Japanese scientists that was led by Saji Hameed.
However, its associated impacts are well-documented, especially over East Africa and Australia.
When a positive Indian Ocean dipole event occurs, the rainfall tends to move with the warm waters, such that more rainfall than normal is experienced over the East African countries while the colder waters over the east of the Indian Ocean dries Australia and is accompanied by heat waves.
A neutral phase would mean sea temperatures that are close to average across the tropical Indian Ocean basin, with no identifiable related weather and climate anomalies in the adjacent Indian Ocean rim countries.
A negative dipole phase would bring about near opposite conditions compared to the positive dipole impacts.
Over southern Africa, the impacts are similar to those over Australia, and hence opposite those occurring in East Africa.
The current positive IOD and its impacts in other regions
The IOD’s positive phase this season has acquired a record intensity, surpassing the previous record-breaking positive IOD events of 1961, 1994 and 1997.
This ongoing extreme positive IOD event continues to affect people and ecosystems in the Indian Ocean rim countries and elsewhere.
The result of the current unusually strong positive IOD event has been higher-than-average rainfall and floods in eastern Africa and droughts in south-east Asia and Australia.
In order to appreciate the nature and magnitude of harm that has been associated with the potential impacts of the current positive IOD, the following is a chronicle of events which have so far been inflicted in its predominant geographical sphere of influence.
Already parts of East Africa have been severely devastated by the ongoing positive IOD-related exceptionally heavy rains that are accompanied by widespread flash floods and landslides since the beginning of the rainfall season.
This region of the Horn of Africa has been recording up to 300 percent above average rainfall from October, according to the Famine Early Warning Systems Network.
These heavy downpours, whose occurrence is set to continue till the expected termination of the IOD event in early January 2020, has so far resulted in heavy fatalities, destruction of property, and significant crop damage and infrastructure within parts of Djibouti, Ethiopia, Kenya, Uganda, Tanzania, Somalia and South Sudan.
More than 300 people have been reported dead and 2,8 million people have been affected, with hundreds of thousands having been forced from their homes, according to the UN Office for the Coordination of Humanitarian Affairs.
These sustained severe floods are now threatening a resurgence of infectious diseases such as malaria and Rift Valley Fever over the affected regions.
On the other side of the Indian Ocean, thousands of kilometres away in Australia, the opposing eastern pole of the IOD has not spared the region in form of destruction.
Australia has recorded its driest spring on record, which has been accompanied by similarly record-breaking spring temperatures.
The City of Perth has posted its hottest ever start to summer, with maximum temperatures hovering around 40C.
Several other towns and cities have also send their previous record temperatures tumbling.
The resulting record-breaking climatic conditions caused Australia’s wheat output to drop 45,6 percent in 2019 from a record high in 2017.
The combination rendered by a mix of these extra harsh climatic factors has also triggered heat waves that helped spark and fan a series of great bushfires across the country.
About 100 bushfires so far raged in the Australian state of New South Wales alone, with the most severe forming into a “mega blaze” north of Sydney.
As a result, this most populous city has been choking under a blanket of thick smoke funnelling in from the fire zones.
Its air quality exceeded prescribed hazardous levels on most occasions.
In fact, the bushfire season began much earlier than usual in eastern Australia and has been one of the most devastating on record, based on the area burnt.
In the adjacent Indonesia, haze from uncontrollable forest fire caused cancellation of flights, closure of schools, and respiratory health problems in the country including her neighbours.
The raging fires also drastically reduced forest cover and the resulting habitat loss which poses grave threats to the survival of rainforest dwelling species such as orangutans, tigers, and sunbears.
Severe floods in India and Pakistan during the southwest monsoon similarly resulted in losses of life, infrastructure, and agricultural productivity.
Meanwhile in Japan, the summer brought record-breaking heat, prompting much heated debate across the nation and its media on whether the 2020 Tokyo Olympics will be adversely affected by similar weather conditions.
Southern Africa’s summer impacts of the current positive IOD
The current positive IOD event peaked in mid-October when the waters around east Africa were about two degrees Celsius warmer than those near Australia.
Over the early summer months through to December, this event maintained the acquired record breaking extreme intensity — being the strongest event in the satellite era (post 1978).
In this regard, this intense phenomenon has exceedingly warmed the western Indian Ocean waters whilst drastically cooling the east.
Such a pattern of SSTs tends to concentrate moisture over the western Indian Ocean, hence denying convergence of moisture over the adjacent south eastern subcontinent of southern Africa.
The forecast of the positive IOD indicates that it is expected to remain at record strength even into early January or slightly beyond, where it is expected to interfere with the southward migration of the Inter Tropical Convergence Zone (ITCZ), the main rain bearing system of southern Africa.
In this case, the positive IOD is bound to divert the normal movement of the south easterlies which are the main defining component that uplifts the relatively warm and humid tropical air mass during the convergence process of the ITCZ.
Consequently, the absence of the south-easterlies over the subcontinent has restricted the southward movement of the ITCZ, resulting in the current prolonged mid-season dry spell over the region.
This is already having visible negative impacts on crops and dam levels over most of the southern African countries.
In fact, it is on record the over the sub region, a wet Christmas usually coincides with a good season whilst a dry one is synonymous with seasonal rainfall deficits.
Research on the IOD impacts over southern Africa has shown that when a positive IOD is at play, the best that the region can get is just an average rainfall amount that is poorly distributed, otherwise it will be an outright drought.
It is also noted that virtually all extreme droughts over southern Africa are linked to the impact of the positive IOD, either in isolation or in combination with the Pacific El Nino.
The drought mainly results from the ITCZ which will have been rendered inactive by the presence of the positive IOD.
Of late, the impacts of the IOD have not only been restricted to rainfall deficits, but has been accompanied by heat waves as is being witnessed during the current rainfall season over southern Africa.
SADC Climate Services Centre (CSC) has even issued for the first time in its history, extreme temperature alerts for the region during the last week of the month of October 2019.
The rainfall impacts due to the IOD largely occur concurrently over East Africa and Australia, but are delayed over southern Africa where they become more pronounced from late December.
Hence, the IOD rainfall impacts, though largely restricted to the later part of summer, are quite similar to those over Australia, but opposite to those over East Africa where they manifest much earlier in spring.
As such, the fortunate aspect about the delayed regional rainfall impact is that the IOD initially fires warning shorts over the Horn of Africa and Australia in early spring before turning its ugly head towards southern Africa during late summer.
For some strange reasons, which is currently an area under research, the IOD impacts seem to have its epicentre over Zimbabwe, meaning that the strongest effects manifest over this country.
These impacts are primarily effected through its influence on the ITCZ, the main rain producing regional system from end of December.
During the positive IOD interference, the south easterlies which reinforce the activity of the ITCZ, are forced to divert to the warm western IO waters rather than to the subcontinent.
This action explains why the current mid-season dry spell, which normally marks the transitional period to the regional impact from the ITCZ, has been prolonged.
As it stands now, the current prolonged dry spell is not expected to end any time soon, but to stretch to the near end of the first week of January (5th or 6th) beyond which a moderate wet spell is expected to set in.
After the present dry spell, we may only realise rainfall from pulses from the ITCZ which will be oscillating over Zambia to the north rather than from a downpour that is usually realised when the ITCZ migrates southward to predominantly anchor over southern Africa.
It is very unlikely to get an active ITZC over southern Africa under the prevailing positive IOD conditions.
However, all hope for the current rainfall season is not completely lost for the region of southern Africa, especially the eastern parts.
The warm waters of the western Indian Ocean, including the Mozambique Channel is giving birth to quite an unusually high number of tropical cyclones.
This observation raises the probability of having one or two stray tropical cyclones making landfall over the eastern coast of southern Africa.
Although the impacts of tropical cyclones are equally devastating, some areas which are not directly hit by the torrential rains may benefit.
This could be either through the watering of pastures, filling of dams and raising the levels of depleted water tables from moderate rainfall which comes from distant and less intense cloud bands that will be linked to the core of the tropical cyclone.
Global research on the current unique positive IOD event of 2019
In advancing climate science and applying it for societal benefit, a clear and detailed understanding of physical mechanisms underlying the climate system is essential to developing reliable predictions and robust mitigation strategies.
Inter-annual climate events such as the ENSO and IOD events provide unique opportunities to deepen knowledge of climate mechanisms, especially since the climate perturbations forced by these events are of basin or larger scales and persist for several seasons.
Ever since the discovery of the IOD phenomenon by a group of scientists led by Saji Hameed in 1999, Japan has led the IOD research in understanding the physics of the phenomenon as well as its simulation and prediction.
In the same vein, Japan has also initiated the related observational networks to study the phenomenon and in pioneering research on its societal applications
The ongoing positive IOD event is distinct in all respects.
The phenomenon is not being moderated from the Pacific Ocean ENSO, which also has a significant impact on the seasonal rainfall of Southern Africa, as ENSO is predominantly in the neutral phase at the moment and neither is there a regulatory effect from the Atlantic Ocean.
The IOD event is unique in terms of not only its unprecedented amplitude in the satellite-era, but also in that it occurred in isolation without the complicating influence of similar scale phenomena in the tropical Pacific or the Atlantic oceans.
In fact, since its early spring development, the IOD is poised to remain the sole dominating inter annual climate forcing from the global tropics for whole of the summer of 2019.
It is worth noting that this Indian Ocean-based phenomenon is having its greatest intensity in the satellite era, the period when surface temperature and other measurements could be verified by more reliable satellite observations.
This makes this IOD event to be well-sampled — being observed to be the first extreme singular IOD occurrence that is devoid of any moderating interference from other climate modes from neither the Pacific nor the Atlantic Ocean.
The undiluted IOD influence is being monitored through a wide range of insitu and satellite-based instruments measuring climate parameters such as sea surface temperatures, sea-level, and surface winds and environmental parameters such as ozone, carbon monoxide, aerosol and ocean-colour etc.
As such this current extreme IOD event indeed provides such rich observationa data are a rare opportunity for climate and related sciences research.
While the current impacts are not really unique to the positive IOD event in terms of occurrence, the high magnitude of the severity of the impacts of this extremely strong 2019 IOD has reactivated scientific and public awareness of the phenomenon, reminiscent of the situation in the 1970s and 1980s for El Nino.
Prior to 1972, El Nino was relatively unknown except to specialist oceanographers. However, the devastating societal and ecosystem impacts of the strong events of 1972 and 1982 led to coordinated international efforts to understand El Nino and predict its impacts.
These concerted efforts dramatically improved our understanding of multiple aspects of the climate system, leading to the development of coupled climate models that can predict El Nino with several months of lead time.
The impacts of the IOD events are poised to remain with us for at least the foreseeable future. With the advent of climate change, the extreme climate and weather events caused by the IOD are predicted to become more common in the future as greenhouse gas emissions increases.
In actual fact, the projections under climate change, according to a 2014 study published in Nature, scientists in Australia, India, China and Japan, are that the frequency of the extreme positive dipole events would increase this century from one in every 17,3 years to one in every 6,3 years.
This phenomenal increase in the frequency is not only disturbing, but should be quite alarming for the Indian Ocean rim countries which are within the impact domain of the IOD, including southern Africa.
Therefore, inaction is not an option as the fatal results over the region, similar to or worse than those explained here are eminent.
Considering this rare characteristics of this phenomenon, that are accompanied by glaring and highly devastating impacts, the initiation of a joint international effort to understand it with the aim of ameliorating the associated societal impacts has become imperative.
Japan has once again led this initiative to examine the climatic, environmental, and health impacts of the extreme positive IOD event of 2019.
Bindura University of Science Education in Zimbabwe is also involved with a specific task to examine the IOD impacts on the southern African region during the current rainfall season of 2019-2020.
This being said, advances in technology is making predictions of short-term events of less than three months almost impossible to miss for a well-trained meteorologist.
It is, therefore, up to the governments of southern Africa to take a leaf from this analysis of climatic events and consider the option for precautionary action whilst time allows.
This may save life and property from the impeding severe drought, especially that imports of food to get to the intended communities may take several weeks to months.
At the same time, Australia whose positive IOD impacts are quite similar to those over southern Africa, is already taking a proactive stance by bracing for the worst in her preparation to reduce the after effects of the current positive IOD event.
The Australian Bureau of Meteorology has already issued a stern warning to its communities, advising them to prepare not only for an extreme drought but for more severe fire danger, with a high chance of severe heat waves for much of the country throughout the current summer season.
Given the overwhelming scientific evidence on the extent and magnitude of the expected impacts from this positive IOD on southern Africa, I do not see any reason why governments of southern Africa should not be moved and similarly prepare for the worst in the current 2019-2020 rainfall season.
In any case, preparing for the worst in disaster risk reduction terms, is defined as a worthwhile bonus.
This work was prepared by Professor Desmond Manatsa of Bindura University of Science Education, with some contributions from Professor Saji Maheed, a Japanese climate scientist who led a team of Japanese colleagues that discovered the Indian Ocean Dipole in 1999. He is now leading the team of global scientists from different continents analysing the global impacts of the current positive IOD while Professor Manatsa has been assigned the role to examine the section on the ongoing positive IOD impacts over Southern Africa. Professor Manatsa is also the current president of the Africa Alliance for Disaster Risk Institutes (AADRI) as well as being a board member of the Global Alliance for Disaster Risk Institutes (GADRI) that is based at Kyoto University in Japan, where AADRI is affiliated.