livestock – Cabot Institute for the Environment blog

East Africa must prepare for more extreme rainfall during the short rainy season – new study

Posted on March 11, 2024 by amanda.woodman-hardy

Rainy season in Kenya

East Africa has recently had an unprecedented series of failed rains. But some rainy seasons are bringing the opposite: huge amounts of rainfall.

In the last few months of 2023, the rainy season known as the “short rains” was much wetter than normal. It brought severe flooding to Kenya, Somalia and Tanzania. In Somalia, more than 2 million people were affected, with over 100 killed and 750,000 displaced from their homes. Tens of thousands of people in northern Kenya lost livestock, farmland and homes.

The very wet short rainy seasons are linked to a climate event known as a positive Indian Ocean Dipole (known as the “IOD”). And climate model projections show an increasing trend of extreme Indian Ocean dipoles.

In a new research paper, we set out to investigate what effect more frequent extreme Indian Ocean Dipole events would have on rainfall in east Africa. We did this using a large number of climate simulations and models.

Our results show that they increase the likelihood of very wet days – therefore making very wet seasons.

This could lead to extreme weather events, even more extreme than the floods of 1997, which led to 10 million people requiring emergency assistance, or those of 2019, when hundreds of thousands were displaced.

We recommend that decision-makers plan for this kind of extreme rainfall, and the resulting devastating floods.

How the Indian Ocean Dipole works

Indian Ocean Dipole events tend to occur in the second half of the year, and can last for months. They have two phases: positive and negative.

Positive events occur when the temperature of the sea surface in the western Indian Ocean is warmer than normal and the temperature in the eastern Indian Ocean is cooler than normal. Put simply, this temperature difference happens when winds move warmer water away from the ocean surface in the eastern region, allowing cooler water to rise.

In the warmer western Indian Ocean, more heated air will rise, along with water vapour. This forms clouds, bringing rain. Meanwhile, the eastern part of the Indian Ocean will be cooler and drier. This is why flooding in east Africa can happen at the same time as bushfires in Australia.

The opposite is true for negative dipole events: drier in the western Indian Ocean and wetter in the east.

Under climate change we’re expecting to see more frequent and more extreme positive dipole events – bigger differences between east and west. This is shown by climate model projections. They are believed to be driven by different paces of warming across the tropical Indian Ocean – with western and northern regions projected to warm faster than eastern parts.

Often heavy rain seasons in east Africa are attributed to El Niño, but recent research has shown that the direct impact of El Niño on east African rainfall is actually relatively modest. El Niño’s principal influence lies in its capacity to bring about positive dipole events. This occurs since El Niño events tend to cool the water in the western Pacific Ocean – around Indonesia – which also helps to cool down the water in the eastern Indian Ocean. These cooler temperatures then help kick-start a positive Indian Ocean Dipole.

Examining unprecedented events

Extreme positive Indian Ocean Dipole events are rare in the recent climate record. So to examine their potential impacts on rainfall extremes, we used a large set of climate simulations. The data allowed us to diagnose the sensitivity of rainfall to larger Indian Ocean Dipole events in a statistically robust way.

Our results show that as positive dipole events become more extreme, more wet days during the short rains season can be expected. This effect was found to be largest for the frequency of extremely wet days. Additionally, we found that as the dipole strength increases, the influence on the most extreme days becomes even larger. This means that dipole events which are even slightly “record-breaking” could lead to unprecedented levels of seasonal rainfall.

Ultimately, if positive Indian Ocean Dipole seasons increase in frequency, as predicted, regular seasons of flooding impacts will become a new normal.

One aspect not included in our analysis is the influence of a warmer atmosphere on rainfall extremes. A warmer atmosphere holds more moisture, allowing for the development of more intense rain storms. This effect could combine with the influence of extreme positive dipoles to bring unprecedented levels of rainfall to the Horn of Africa.

2023 was a year of record-breaking temperatures driven both by El Niño and global warming. We might expect that this warmer air could have intensified rain storms during the season. Indeed, evidence from a recent assessment suggests that climate change-driven warming is highly likely responsible for increased rainfall totals.

Responding to an unprecedented future

Policymakers need to plan for this.

In the long term it is crucial to ensure that any new infrastructure is robust to withstand more frequent and heavier rains, and that government, development and humanitarian actors have the capacity to respond to the challenges.

Better use of technology, such as innovations in disseminating satellite rainfall monitoring via mobile phones, can communicate immediate risk. New frontiers in AI-based weather prediction could improve the ability to anticipate localised rain storms, including initiatives focusing on eastern Africa specifically.

Linking rainfall information with hydrological models designed for dryland environments is also essential. These will help to translate weather forecasts into impact forecasts, such as identifying risks of flash flooding down normally dry channels or bank overflow of key rivers in drylands.

These technological improvements are crucial. But better use of the forecast information we already have can also make a big difference. For instance, initiatives like “forecast-based financing”, pioneered by the Red Cross Red Crescent movement, link forecast triggers to pre-approved financing and predefined action plans, helping communities protect themselves before hazards have even started.

For these endeavours to succeed, there must be dialogue between the science and practitioner communities. The scientific community can work with practitioners to integrate key insights into decisions, while practitioners can help to ensure research efforts target critical needs. With this, we can effectively build resilience to natural hazards and resist the increasing risks of our changing climate.

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This blog is written by David MacLeod, Lecturer in Climate Risk, Cardiff University; Erik W. Kolstad, Research professor, Uni Research; Cabot Institute for the Environment member Katerina Michaelides, Professor of Dryland Hydrology, School of Geographical Sciences, University of Bristol, and Michael Singer, Professor of Hydrology and Geomorphology, Cardiff University. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Working with the weather to manage parasites of livestock in changing climates

Posted on October 27, 2016April 6, 2023 by janet.crompton

Parasites can be found in every environment on earth and infect a wide range of hosts – birds, fish, plants, insects, wild animals, domesticated animals and humans. When parasites are discussed they often trigger an “ewww” reaction. However, they have much more serious economic, food security and animal health and welfare impacts when they infect grazing livestock. Grazing livestock contribute greatly to food security and this is not going to change any time soon. Not only is the global population (and therefore food requirement) growing, there is an increasing demand for animal-based food products in developing regions and there is an essential role of animal products in marginal environments where crop production is infeasible. Parasite control is therefore vital, but is not easy to achieve.

Many parasites have complex lifecycles which depend upon specific climatic conditions. For instance, temperature and moisture determine development rates and survival. Farmers could once use this to their advantage as the predictable, seasonal weather patterns led to predictable, seasonal patterns of parasites. Reliable livestock husbandry practices therefore developed for parasite management. However, in recent years there have been changes in climate and less predictable weather patterns. Traditional management practices are often no longer effective as parasites are being found in unexpected regions and at unexpected times of year. What’s more, whilst other organisms are being put under threat by climate change, parasites are successfully evolving and adapting to these changes in environment due to their short reproductive cycles.

Predicting the risk of infection to parasites involves multiple areas of expertise. An in-depth knowledge of parasite characteristics is essential, and needs to be updated as they evolve. Accurate forecasts for climate are also needed to help predict which regions may have an environment suitable for the parasite and changes to its seasonality. An accurate forecast for weather (daily climatic conditions) is essential for certain parasites. Combining historical data with forecasts, knowledge of the parasite’s requirements for development and farm characteristics (such as altitude and orientation) within complex models gives precise information on infection risk and helps farmers to be one step ahead of the parasites. Technology is also aiding the rapid diagnosis of specific parasite infections to guide effective management practices.

Despite these advancements in parasite control, uptake of the technologies by farmers is often slow. The science behind parasites and the models developed are complicated and daunting. Livestock farming is demanding, both economically and in terms of labour. Therefore farmers need these complex technologies to be transformed into tools that are still effective, yet simple and easy to integrate into their current practices. They need to feel confident in using the tools and understand the benefits that come with them – not the science. These benefits include more efficient animals, both economically and environmentally, and improved animal health and welfare.

There is still much to learn about parasites. The rapid changes to the environment, the livestock industry and the parasites themselves means that this is an area of work that will be ongoing for the foreseeable future. There is a huge need for collaboration between disciplines to not only develop the tools, but also to communicate their need and promote their use on farms. This barrier to technology uptake could be a bigger hurdle for scientists than technology development itself.

This blog is written by Cabot Institute member Olivia Godber, a PhD student in the School of Biological Sciences at the University of Bristol.

Do not make policy during the middle of a flood crisis

Posted on March 14, 2014April 19, 2023 by janet.crompton

Across the country, we have seen our neighbours’ homes and farms devastated by the floods. We understand their anger and frustration. We understand their demands for swift action.

What they have been given is political gamesmanship. Blame shifting from party to party, minister to minister, late responses, dramatic reversals of opinion. It reached its well-publicised nadir this past weekend, with Eric Pickles’ appearance on the Andrew Marr show:

‘I apologise unreservedly and I’m really sorry that we took the advice; we thought we were dealing with experts.’

Throwing your own government experts to the wolves is not an apology.

This political vitriol, at least with respect to the Somerset Levels, all appears to come down to a relatively simple question – should we have been dredging?

This is not a simple question.

It is an incredibly complex question, in the Somerset Levels and elsewhere, and this simplistic discussion does the people of those communities a great disservice.

Image by Juni

But more fundamentally, this is not the time to be deciding long-term flood mitigation strategy. In times of disaster, you do disaster management. Later, you learn the lessons from that disaster. And finally, informed by evidence and motivated by what has happened, you set policy. And that, to me, is the most frustrating aspect of the current political debate. In an effort to out-manoeuvre one another, our leaders are making promises to enact policy for which the benefits appear dubious.

So, what are some of the issues, both for Somerset and in general?

First, the reason the rivers are flooding is primarily the exceptional rainfall – January was the wettest winter month in almost 250 years. This rain occurred after a fairly damp period, so that the soil moisture content was already high. However, these issues are exacerbated by how we have changed our floodplains, with both agricultural and urban development reducing water storage capacity.

Second, as the 2013-2014 flooding crisis has illustrated, much of our nation is flood-prone; however, those floods come in a variety of forms and have a range of exacerbating causes – some have been due to coastal storm surges, some due to flash floods caused by rapid flow from poorly managed lands and some due to sustained rain and soil saturation. We have a wet and volatile climate, 11,073 miles of coastline and little geographical room to manoeuvre on our small island. Our solutions have to consider all of these issues, and they must recognise that any change in a river catchment will affect our neighbours downstream.

Flooding on West Moor, Somerset Levels
Image by Nigel Mykura

Third, returning to the specific challenge of the Somerset Levels, it is unclear what benefit dredging will have. The Somerset Levels sit near sea level, such that the river to sea gradient is very shallow. Thus, rivers will only drain during low tide even if they are dredged. And widening the channels will actually allow more of the tide to enter. Some have argued that in the past, dredging was more common and flooding apparently less so. However, this winter has seen far more rain and our land is being used in very different ways: the memories of three decades ago are not entirely relevant.

Fourth, where dredging is done, it is being made more costly and challenging by land use practices elsewhere in the catchment. The rivers are filling with sediment that has eroded from intensively farmed land in the headwaters of the catchments and from the levels themselves. Practices that have greatly accelerated erosion include: heavy machinery operations in wet fields; placement of gates at the bottom of hillslopes so that sediment eroded from the field is very efficiently transported to impermeable road surfaces, and thence to streams downslope; cultivation of arable crops on overly steep slopes (increasing the efficiency of sediment transport from land to stream); overwintering of livestock on steep slopes; and excessive stocking densities on land vulnerable to erosion.

Image by Nicholas Howden

Nutrient enrichment from livestock waste and artificial fertilisers (when used in excess of crop requirements) also contribute to the dredging problem. The nutrient loading often exceeds the system’s recycling capacity, such that nutrients flow into ditches and waterways, stimulating growth of aquatic plants that can readily clog up the minor ditches and waterways. With less space to dissipate water within the network, it is forced into the main channel. In other words, some of these floods are a subsidised cost of agriculture – and by extension the low costs we demand of our UK-produced food.

And finally, if we are going to consider long-term planning, we must consider climate change impacts. Flooding will become worse due to sea level rise, which has already risen by about 12cm in the last 100 years, with a further 11-16cm of sea level rise projected by 2030. It is less clear how climate change will affect the intensity and frequency of these particularly intense rainfall events. Although almost all projections indicate that dry areas will become dryer and wet areas will become wetter, predictions for specific geographical regions are highly uncertain. And our historical records are not long enough to unravel long-term trends in the frequency of uncommon but high impact weather events. This should not be reassuring – it is another major element of uncertainty in an already complex problem.

As challenging as these issues are, they are not intractable. The solutions will involve stronger planning control and scientifically informed planning decisions (including allowing some areas to flood), a reconsideration of some intensive farming practices, some dredging in key areas, some controlled flooding in others, and better disaster management strategy for when the inevitable flooding does occur. But now is not the time to resolve such a complicated knot of complex issues. It is certainly not the time to offer false promises or miracle cures.

Now is the time to help our neighbours in distress, listen to their stories, and remember them when the floodwaters recede. And then we should let our experts get on with their jobs.
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This blog is co-written by Professor Paul Bates, Professor Penny Johnes (Geographical Sciences), Professor Rich Pancost (Chemistry) and Professor Thorsten Wagener (Engineering), all of whom are senior members of the Cabot Institute at the University of Bristol.

This blog post was first published in the Guardian on 12/02/2014, titled Flood crisis: Dredging is a simplistic response to a complex problem.

If you have any media queries relating to this blog, please contact Paul Bates or Rich Pancost (contact details in links above).

Prof Paul Bates, Head of
Geographical Sciences

Prof Rich Pancost, Director of the
Cabot Institute