The year 2024 is not only expected to be the warmest year on record, at the time of writing, but is also a year that has seen a multitude of extreme events, including severe flooding around the world. Particularly devastating floods were experienced in Afghanistan, Pakistan, Brazil, Uruguay and multiple places in Europe, such as the deadly floods in Spain in late October.

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As a warmer world makes heavier rainfall more probable in many regions, these floods were likely to some degree affected by climate change. But they also highlight the additional factors that are needed for meteorological hazards to evolve into disasters, many of which are controlled by humans.

There are often three dimensions that determine the overall danger from a weather event: hazard, exposure and vulnerability. Hazard describes the physical conditions that have the potential to cause damages. Exposure describes the number of people, infrastructure and assets affected. And vulnerability determines the damage that a hazard does if an area or a population is exposed.

When considering the physical hazard, meteorological extremes do not necessarily have to develop into disaster risks. In the case of flooding, heavy rainfall does not automatically result in extreme water levels, unless it is channeled through runoff and constrained by topography to sustain high water levels. For example, heavy rain over flat soils that can absorb large amounts of water will be less of a danger than the same amount of rainfall in a confined mountain valley with impermeable ground.

These environmental factors do not have to be static. For example, the flooding in Afghanistan and Pakistan in the boreal spring of 2024 has been linked to increased runoff as the soils were not able to absorb rainfall after an exceptionally dry winter, making the flooding more severe than it would have been in other years. In many other cases, humans shape these environments, for example, by urbanization, deforestation or rerouting rivers, and thus influence the streamflow and the likelihood that extreme rainfall can develop into high water levels.

Although humans have some influence on the hazard dimension, they have even stronger control over the exposure and vulnerability dimensions. Just because heavy rainfall occurs over large population centres it does not mean that many people have to be exposed to flooding. Protective infrastructure such as floodplains and dams can keep the water away from settlements, and warning systems can decrease the vulnerability of communities.

The importance of these measures has been demonstrated this year. In the boreal autumn, persistent heavy rainfall caused widespread flooding throughout central Europe. While large parts of Austria saw high water levels, the city of Vienna was far less affected than its surrounding areas, likely as a result of the flood protection installed decades earlier.

But even if protective infrastructure and warning systems are in place, there are still human decisions that can affect the degree of damage a specific hazard can create. For example, it has been argued that the death toll of the flooding in Spain in late October could have been massively reduced if warnings were sent out earlier.

These examples show that many more factors than just meteorological extremes are necessary to make a climate disaster. Still, debates often focus too narrowly on meteorological extremes. This is likely to have been influenced by advances in recent decades that have resulted in the meteorological components of hazards being better understood than other factors.

For example, climate models have become much better in representing extreme rainfall, while actual runoff and protective infrastructure are far less well represented in models. This means that larger-scale studies on rainfall extremes are becoming more reliable, but they can often only give limited insights on the actual flooding risks.

Another important advance has been the attribution of the meteorological components of specific events to climate change. This December marks the twentieth anniversary of one of the first studies that quantified the human contribution to a heatwave1, laying the groundwork for the field of attribution science. This research has since shaped reporting on many events, even as the authors themselves warn against a too simplified interpretation2.

This and other research has shown many times that climate change drives much of the risks of climate hazards and that mitigation of greenhouse gas emissions is the most efficient way of reducing climate-related disasters. But focusing mainly on the meteorological components of disasters must not distract from the many ways in which humans can influence how deadly a specific event gets.