Understanding slow and rapid onset disasters

Alex Randall

Alex is programme coordinator of the Climate and Migration Coalition

Slow and rapid onset disasters: it’s a common distinction, but what does it mean?

Not all disasters happen at the same speed. Consider two examples.

1. Typhoon Haiyan / Yolanda made landfall in the Philippines on the 8th of November. It had been identified as one of the most powerful Typhoons ever recorded only hours before. In a few hours it had killed 6,000 people and injured nearly 30,000. The typhoon displaced 4 million. By the 9th of November the storm had moved into Vietnamese and Chinese territory.

2. In July 2011 a severe drought hit the Horn of Africa. It lasted almost an entire year. By September 2012 nearly a million people had fled Somalia to camps in Kenya and Ethiopia. Early warning systems first forecast the looming disaster 11 months before it hit. The massive displacement was created partly by the fact the region had been made more vulnerable by previous droughts.

Rapid-onset disaster unfold almost instantly, slow-onset disasters can be predicted much further in advance and unfold over months or even years. Rapid-onset disasters tend to create their destruction through the immediate physical impacts. Slow-onset disasters also create crises through the economic and social impacts of the disaster.

Slow-onset Rapid-onset
Drought Cyclones, Typhoons, Hurricanes
Desertification Storm surge
Sea level rise Flash flooding
Erosion Earth Quakes
Water salination Volcanic eruptions

How are slow-onset disasters affected by climate change

The key question is – how are each of these disasters affected by climate change? Which of them might become worse as the planet warms? This info graphic gives a simple indication of how much each hazard will be affected by climate change, and how strong the evidence for that effect is.

How do slow-onset disasters affect migration, how is it different from rapid-onset?
We can analyse this by looking at how slow and rapid-onset disasters create different kinds of human movement.

Do they both create forced movement?

Yes. This is the most obvious similarity. People are forced to move by both kinds of disasters. In our two earlier examples (Typhoon Haiyan and the Horn of Africa drought) millions of people had no choice about moving. They simply had to move in order to survive.

Do they both create voluntary movement?

Sudden disasters tend not to create voluntary movement. Slow-onset disasters can create both forced and voluntary movement. The slowly unfolding pace of slow-onset disasters means that some people might choose to move, before they are forced to move later on. Often people with slightly more money or resources will leave an area as conditions get worse. Clearly this movement is not entirely voluntary. However it may leave people with more choices about when they move and where they go.

Do they both create internal movement?

Yes. In fact the vast majority of people who are affected by both rapid and slow-onset disasters move within their own country.

Do they both create cross border movement?

Slow-onset disasters are more likely to create cross border movement. For example during the Horn of Africa drought millions of people fled across international borders into neighboring countries. As we’ve pointed out in previous posts, this was the result of a complex web of environmental, economic and conflict drivers. During sudden disasters people tend to move short distances. They have little or no time to collect possessions, and often move to the nearest safest place.

“The water came at night and we didn’t have time to save our belongings; we had to chose whether to save our children and ourselves or our property and assets, so we chose to save our kids. We left everything and ran to save our lives.” Unnamed survivor of the 2010 floods (World Food Programme)

There are circumstances in which rapid-onset disasters might influence the choices of migrants who are already outside their own country. For example a large number of people from the Philippines work overseas, and the Typhoon will have affected their decisions about if and when to return.

Do they both create internal movement?

People affected by slow and rapid-onset disasters often express a deep desire to return, as do many people displaced by factors other than disasters.

People fleeing both kinds of disasters often do return. In the case of slow-onset disasters like drought, people will often return when conditions improve. With rapid-onset disasters people will often return quickly to take part in reconstruction. This can leave both groups vulnerable if the same disaster strikes again. Some kinds of slow-onset disasters might be permanent, and might create permanent displacement. For example sea level rise is already creating permanent movement away from low lying areas.

Desertification in many cases is not reversed and creates situations where farming may not be possible again. In these circumstances the movement may be permanent rather than temporary. Some kinds of slow-onset disasters may create seasonal and circular migration. For example if altered rainfall patterns make farming less profitable people may move during dryer periods and then return as conditions change. People might also seek work elsewhere during quieter parts of the agricultural year, and then return when more work is available.

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