Warmer temperatures in the atmosphere mean that air is able to hold more water vapor. This is leading to more frequent, heavier rainfall events.

From the United Nations Environment Program:

Climate change and floods—how they are connected

Floods are made more likely by the more extreme weather patterns caused by long-term global climate change. Change in land cover—such as removal of vegetation—and climate change increase flood risk.

Extreme floods can be triggered by intense precipitation, longer duration, close repetition of precipitations or a combination of these. In the case of intense precipitations, such as was experienced in the United Kingdom, the Intergovernmental Panel on Climate Change in its comprehensive assessment of the physical science basis of climate change found that there is high confidence that this is an increasing trend in Europe, especially for winter flooding.

“While it is difficult to make a direct link between an individual extreme event and climate change, it is clear that we need to be prepared to face more intense and more frequent extreme hydro-meteorological events due to climate change,” says Pascal Peduzzi, Director of the United Nations Environment Programme’s (UNEP) Global Resource Information Database in Geneva.

Rising global temperatures mean more rain

With higher temperatures, we have more energy in the Earth’s system. Higher ocean water and air temperatures increase the possibility for evaporation and therefore cloud formation. At higher temperatures, the air can hold more moisture content. This can lead to an increase in precipitation intensity, duration and/or frequency.

Temperatures increase faster at higher latitude than at the equator. It results in a smaller temperature gradient between mid-latitude and polar temperatures, which can affect the jet stream. For the North Atlantic region, research points to a potential higher frequency of extreme hydro-meteorological events, such as heavy storms in winter, or prolonged drought in summer.

Temperatures are on the rise

Our global temperature in January was the highest ever on record. The global average temperature is now 1.1oC higher than the beginning of last century. UNEP’s World Environment Situation Room includes regularly updated information about  global temperature anomalies, and this graph shows that January 2020 was the warmest January since records began, rising to 1.19oC above pre-industrial levels.

Above average temperatures per month, showing that the month of Jan 2020 was the warmest ever recorded.
Source: UNEP World Environment Situation Room: wesr.unep.org

What can we expect?

Extreme flooding will continue to be concentrated in regions where humans have built on floodplains or low-lying coastal regions. As global warming increases the likelihood for more extreme weather events to occur, risks will expand beyond the high-risk areas known today. More extreme flooding must be expected, and for the towns and cities where flooding has already occured, theirs will no longer be a ‘once in a lifetime’ risk but now far more frequent.

The reality is that this is the world we live in with 1.1oC of warming. These records temperatures, record floods are not anomalous, they are the beginning of a new norms, and the new records will continue to be exceeded, year after year.

What will things be like in a few decades when we hit 1.5oC? As affected communities drain, dredge, dry out and count the cost of lost belongings, ruined homes and businesses, as people live with lingering damp, and new fears of future storms, it appears that much needs to be done to prepare ourselves to face our future reality.

Everyone – governments entities at all levels, business, civil society, individuals — need to be prepared to face more extreme weather events as the climate continues to change at an increasing pace. Climate science must be taken into serious account in how we build, adapt and protect our homes, communities, businesses and infrastructure. Most urgently, greenhouse gas emissions must be reduced, so that rising global temperatures can be controlled while this is still possible. Nature-based climate solutions, such as reforestation and land restoration should be considered, as they can both reduce the impacts of extreme weather events and absorb CO2.

2020 is the year that governments will meet to take stock of and increase the ambition of their commitments to taking climate action. It is the year that global emissions must drop by 7.6 per cent, and by 7.6 per cent again every subsequent year until 2030 in order to limit global temperature rise to 1.5 oC, according to UNEP’s 2019 Emissions Gap Report.

Governments, companies, industry and the public of countries of the G20, who are responsible for 78 per cent of emissions, must set targets and timelines for decarbonization. We must embrace the vast social, economic and political opportunities of transitioning to a world powered by renewable energy and the deployment of a multitude of carbon neutral solutions across society.

The insight these floods give to the growing threat of a changing climate are a somber reckoning for the United Kingdom on the year of their presidency of the United Nations Climate Conference.