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Climate change leads to heavier rainfall, increased flood risk

There are uncertainties in climate models and its data output, but there is mounting evidence that points to more frequent or intense heavy rainfall episodes in some regions across Asia and Europe, said Aon in its latest report.

The real-time climate change report, published last week, explored three recent examples of perils that show the fingerprints of climate change: Tropical cyclones, floods in Europe and Asia and wildfires in the US.

In the past decade alone, weather-related disasters have resulted in nearly $3tn in economic damage. This accounts for 85% of total natural peril losses. These losses include direct impacts from such perils as tropical cyclones, flooding, and wildfires - all of which are demonstrating changing behaviour that is putting more lives, livelihoods and property at risk.

Aon estimated that only 31% of these losses have been covered by insurance. Weather-related costs are expected to rise further as events become more frequent or intense, people continue to move into attractive, yet vulnerable areas and the price of daily life becomes more expensive.

Higher temperatures, more rain

One of the core principles of atmospheric science is that warmer air can hold more moisture. As the world has continued to warm at an accelerating rate in recent decades, this has also coincided with more extreme precipitation and subsequent flood events. Two highly anomalous 2021 flood events occurred in Western Europe and Asia. In both instances, the local insurance industry in Germany and China cited the highest natural disaster event pay-outs on record.

There was an historic volume of rainfall that fell in Zhengzhou, China (Henan Province) in mid-July, there was even more focus on the significant protection gap which exists in the country. On 20 July alone, Zhengzhou recorded 612.9mm of rain. This compares to its total annual average rainfall of 640.8mm. Catastrophic flooding occurred that led to more than 552,000 insurance claims being filed. Despite the local Henan insurance industry citing a record $1.9bn in insured loss from the event – the costliest weather event on record for Chinese insurers – it still represented less than 10% of the overall economic loss.

In the same month, across some parts of Germany and elsewhere in western and central Europe, nearly two times the annual July rainfall average fell in a 72 to 96-hour period that overwhelmed many rivers and streams.

There has been vigorous discussion regarding the role of climate change in both events, said Aon. The tremendous volume of rainfall that occurred was consistent with what scientific research continues to highlight as expected with warming in the oceans and atmosphere. Warmer temperatures act as an accelerant to the evaporation process – often over the oceans or other large bodies of water – then place more water/moisture into the atmosphere.

Actions must be taken

One important step to communicate rainfall and flood risk is via return periods – or how likely such an event is expected to occur. For example: A 100-year event means there is a 1% chance of such an event occurring at a location in any given year. It does not mean that it will be another 100 years until another such event happens again. The increased influence of climate change suggests that what is considered a one-in-100-year event today may becoming a one-in-75 or one-in-50-year event in the future. An understanding of this likely shift in event occurrence frequency is highly important when developing risk mitigation and adaptation plans. Such analysis will only enhance the essential need for more regularly updated flood mapping and flood risk tools.


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