Flooding and climate change

Catastrophic flooding, such as one that swept through Valencia during the autumn of 2024, will become increasingly frequent as global temperatures rise. That makes finding ways to adapt – and to finance that adaption – all the more important.

2024 was the hottest year on record and is likely to have been the first year where temperatures are 1.5 degrees centigrade above their pre-warming baseline. Reference temperature is held to be the average for 1850 to 1900   This is already starting to have a significant environmental, social and economic impact, not least flooding. The incidence of super-rare events that lead to massive rainfall increased by 40 per cent in the 30 years to 2013 compared to the 30 years to 1980 Fischer, EM and R Knutti, Observed heavy precipitation increase confirms theory and early models, Nature 2016 , with abnormally heavy precipitation particularly notable across the US’s southern and eastern states, across Europe and Asia, and southern Africa.

As the air grows warmer, it is able to hold more water vapour. Normal atmospheric conditions cause this vapour to precipitate out in the form of rain, hail or snow. For each degree of warming the result is between 1 per cent and 3 per cent more precipitation, which can be heavily concentrated in a particular location. Over the span of hours, as much rain can fall during single major downpour as normally falls over weeks or even months, causing flash floods. Urbanisation, soil erosion, the lack of vegetation and trees, the destruction of wetlands and flood plains that can absorb a rapid increase in water volume all contribute to flooding risk.

Given that progress on climate change mitigation has been insufficient so far, it’s reasonable to assume that average temperatures will climb to at least 2 degrees above baseline by the end of this century. As a result, there has to be a focus on adaptation.

The Intergovernmental Panel on Climate Change notes that flood protection measures can be particularly effective – which is unsurprising given that flood control has a long history. https://www.ipcc.ch/assessment-report/ar6/

This could mean more porous surfaces in cities, planting schemes to protect soil and allow it to absorb more water, the re-introduction of wetlands, the creation of underground reservoirs with capacity to take on large amounts of water for short periods. These and an array of other measures have been applied successfully in cities prone to flash flooding, like Singapore, Rotterdam and Tokyo.

Governments are increasingly aware of the need for adaptation. A growing proportion of climate finance is flowing into it – in 2016, USD10bn went into adaptation compared to USD42bn into mitigation, according to the OECD. By 2022, those respective numbers were: USD32bn, a three-fold increase, and USD70bn, a proportionately smaller 1.6-times rise. And that trend is only likely to continue.

The stark gap between actual investment and what’s needed to reach net zero was highlighted by recent research produced by Pictet in conjunction with the Institute of International Finance. For instance, to reach net zero by the middle of this century, the ratio of low-carbon to fossil fuel energy investment must rise from 2:1 to approximately 7:1 by 2050. This means climate investment will need to increase by as much as USD8 trillion annually through the end of this decade. 

But while rich countries will look for and implement solutions to risks like flooding, poorer countries – which are much more vulnerable to catastrophic events because of a lack of infrastructure and populations pushed into marginal lands – don’t have the wherewithal. That’s particularly inequitable given that these countries also have far lower per-capital emissions of greenhouse gases.

Unfortunately, the biggest proportion of climate mitigation and adaptation finance is steered towards countries with good institutional capacity – and therefore more likely to allocate the money effectively. But these tend not to be the poorest countries with the greatest need. Concerns about mis-appropriation of funds make rich countries reluctant to help financially those with the greatest need. Squaring this circle is a complex challenge.

There is also the question of maladaptation. Some adaptation strategies cause other harms, or aren’t cost-beneficial. So, for instance, building out concrete infrastructure in the form of spillways or emergency canals could do substantial environmental damage and increase greenhouse gas emissions out of proportion to the good it does.

Increased flooding, caused by rising temperatures, shows the necessity of looking beyond mitigation strategies and putting resources into adaptation as well.  This isn’t just an issue for emerging markets. Developed economies are also being forced to recognise the importance of this approach. Though planning and implementation vary, there has been progress. For example, Switzerland’s federal council adopted a climate adaptation plan in 2012. The increasing amount of finance flowing into adaptation in developed countries is a hopeful sign.

One key issue is the insularity with which adaptation policies are being pursued. Funding tends to favour local priorities – the willingness to invest heavily in adaptation strategies abroad is likely to decline. The world is likely to become more fragmented and regionally based when it comes to mitigation and adaptation financing.