There have been successive large scale droughts in East Africa. Shutterstock
Friederike Otto, University of Oxford and Maarten van Aalst, Columbia University
Drought is a common phenomenon in East Africa and has occurred throughout known history. Now, with climate change top of the mind, whenever there’s a drought some are quick to blame climate change as the “cause”.
It’s a fair scientific question to ask: Are these droughts (in part) the result of changes in the earth’s climate brought about by human activities? Or are they solely the result of natural processes?
With successive large scale droughts in East Africa in 2010/11, 2014, 2015 and the ongoing drought, it’s easy to assume climate change caused by human behaviour does indeed play a role.
But droughts are complex extreme events that result from a combination of drivers. In the atmosphere these include; regular climate variability – including day-to-day weather – but also larger seasonal patterns related to cycles, such as El Nino and La Nina. It could be human-induced drivers – like greenhouse gas emissions, or events like volcanic eruptions.
Beyond the atmosphere itself, the condition of water reserves, soil, and vegetation are critical. This could of course be coupled to human activity like irrigation or the number of livestock.
Finally, whether a drought becomes a problem doesn’t just depend on the meteorological conditions but on human decisions on the ground. For example, the effects of a lack of rainfall strongly depends on human vulnerability: how dependent on the climate are people’s livelihoods, do they have assets or financial reserves, and access to markets?
Let’s first look at the science. It’s impossible to say for any single event that it could not have occurred without anthropogenic – caused by human activity – influence. But, in the same way that loading a dice can increase the likelihood of rolling a six, the presence of human-induced climate change can alter the likelihood that a drought will occur.
In the last few years there’s been rapid development in the science of quantifying what role human activity plays in bringing about extreme weather events. These links can be established fairly routinely for some extreme events. But for others we are pushing the boundaries of this new emerging field. Droughts in a relatively data poor region like East Africa belong in this category.
With the World Weather Attribution initiative and the Climate and Development Knowledge Network we are aiming to shed light on this. We are assessing whether climate change, brought about by human activities, altered the risk of the ongoing drought in Kenya and Somalia.
We are not the first to do an “attribution” study like this in East Africa. But we are the first to:
- Use three different and largely independent methodologies to analyse the role of climate change.
- Do this while the event is still unfolding.
- Partner with scientists and practitioners in the region.
Every extreme event attribution study has four outcomes when analysing the impact of human-induced climate change. Climate change can make an event more likely, less likely, not significantly changed its likelihood, or we may conclude that the impact of climate change cannot be reliably assessed. The outcome may also depend on how we define the extreme event in question, for instance in terms of the region, and time period we look at.
High quality observational data and local scientific expertise are crucial. Working with national institutions such as the Kenya Meteorological Department and Ethiopia’s National Meteorology Agency, we identify the event that captures what’s happening on the ground and can be interrogated in climate models.
And we use proven scientific methods. When we initially make these results available, they are not yet peer reviewed. But we apply approaches that have been published in numerous peer-reviewed papers.
East African drought
When examining the current drought in East Africa we can first look at rainfall. We note that some weather stations recorded a decrease in rainfall in recent years. But the region also has large year-to-year natural variability. Combining our multiple methods, we found that human induced climate change is currently not a game changer.
At the same time temperatures in the region are increasing. This may contribute to the current drought conditions. While these increases can be attributed to human-induced climate change, the effect of a changing climate on rainfall is much less straightforward.
On a global average, a warmer atmosphere can hold more water vapour leading to more extreme rainfall. But more greenhouse gases in the atmosphere can also affect what type of weather systems – a lot of low pressure that brings rain or high pressure that brings clear skies – come into a region. This could mean it does rain more on average but at a different place.
Higher temperatures can furthermore affect the interplay between land surface and the atmosphere. For example rain evaporates faster with higher temperatures but once the rain has evaporated higher temperatures don’t have much of an effect. Therefore, it strongly depends on the region and the season how human-induced climate change is affecting rainfall, and if it leads to longer or more frequent dry spells.
This demonstrates that science often doesn’t provide a simple statement, such as “climate change is to blame”. In the case of the drought in Somalia we have no evidence that climate change made this event more likely.
But this does not mean that climate change didn’t play any role.
The less-simple-but-more-honest message from science is that these events are part of the regional climate and even without a strong climate change signal will happen again in the near future. We don’t know if climate change has made them slightly more likely, and furthermore, a period of low rainfall may now also be aggravated by rising temperatures and more research is needed to quantify this effect.
Risk and vulnerability
And that honest message matters even more because of a second element of our analysis: risk is not just determined by what’s happening in the climate, but how something in the climate affects us.
In cases of high vulnerability a relatively moderate lack of rainfall can have a dramatic impact on people’s lives. Somalia is a case in point, where decades of conflict have left the country unequipped to provide assistance in times of crisis.
As a result, it’s important for governments like Kenya’s that are preparing legislation on disaster management to understand the different risk factors that result in a drought.
In the presentation of our findings it has become apparent that scientific evidence is relevant to these discussions. And the demand is there for better data and information. This was made clear in the policy brief on the Kenya drought study.
Honest climate analysis can inform public awareness, policy and practice – especially when events are happening and the appetite to address the problem is highest. Let’s use that window for well-informed debate about addressing rising risk, rather than playing a blame game.
Friederike Otto, Deputy Director and Senior Researcher, Environmental Change Institute, University of Oxford and Maarten van Aalst, Director, Red Cross Red Crescent Climate Centre, Adjunct Research Scientist, Columbia University
This article was originally published on The Conversation. Read the original article.