What would happen to London if it rained as much as Valencia this week?

With Spain tackling its worst flooding disaster in modern history, several countries across Europe will be wondering – could we be next?

Scientists have long warned that climate change means extreme weather will become increasingly frequent and urged nations to be prepared.

So, how would London – home to almost nine million people and the economic centre of the UK – cope if a year’s worth of rain fell in a few hours, as it did in Valencia?

Although it’s difficult to know exactly how it would be impacted, experts have previously said the capital is far from ready for that kind of deluge and could suffer catastrophic consequences.

In January, for example, an independent climate research study, commissioned by London Mayor Sadiq Khan, deemed London seriously underprepared for severe flooding, as well as extreme heat.

The London Climate Resilience Review found a lack of planning will create a ‘lethal risk’ to the most vulnerable communities, the BBC reported.

And in 2021, the non-profit organisation Climate Central shared a worrying map showing which areas of London are particularly vulnerable to flooding and could be regularly underwater by 2030.

The map allows users to explore coastal flood risk and sea level rise projections by decade for anywhere in the world.

Red is used to show areas that could regularly be hit by flooding by 2030 and don’t appear to be protected by dikes.

In West London, most of east Twickenham, Chiswick, Hammersmith and Fulham are covered in red by 2030 – as well asmuch of Kew’s Royal Botanic Gardens.

Almost all of East London could also find itself prone to flooding and sea-level rises, including Greenwich, Stratford, Rotherithe and East Ham.

Like the east and west, a lot of the land south of the river is low and flat.

Battersea, Deptford, Southwark, Camberwell and Peckham could all be vulnerable to flooding by 2030.

Areas in red in north London include Hackney Marshes and Walthamstow reservoirs around the River Lee.

The data is based on a scenario of moderate cuts to pollution, with even more areas covered in red if pollution goes unchecked.

It should be noted that Climate Central, a US based organisation, acknowledges its maps ‘incorporate big datasets, which always include some error’.

It adds: ‘Our maps are not based on physical storm and flood simulations and do not take into account factors such as erosion, future changes in the frequency or intensity of storms, inland flooding, or contributions from rainfall or rivers.’

It also does not take into account the presence of sea defences designed to reduce or mitigate the impact of coastal flooding.

The government’s Environment Agency said London benefits from substantial infrastructure to protect it from coastal flooding, including the Thames Barrier, ‘one of the world’s largest movable flood barriers’.

In reference to Climate Central’s London maps, an Environment Agency spokesperson said: ‘Whilst useful to prompt discussion around the impacts of sea level rise and need to adapt to climate change, the sea level rise prediction made by Climate Central around the future flooding in the area is inaccurate and unsuitable to inform local coastal flood risk.

‘The prediction does not take into account extensive efforts taken to prevent such severe incidents in the future, including the presence of sea defences, which protect communities from flooding.

‘There may also be discrepancies between the climate change scenarios shown on the maps and those we currently advocate as being the most appropriate.’

The London Climate Resilience Review report, meanwhile, said the capital’s main climate risks were rising sea levels, surface water flooding, heat, drought and wildfires.

Review chairwoman Emma Howard Boyd said at the time: ‘London has many good plans and programmes to prepare for climate hazards but we need to recognise that Londoners now face lethal risks, and a step change is needed.

‘Last year was the hottest on record and this is causing chaos and disruption all over the world.

‘London is not immune, as shown by the flash floods in 2021 and a 40C heatwave in 2022.

‘It’s time for the UK, led by its cities and regions, to take action and prioritise adaptation.’

In response Mr Khan said his latest budget proposed an additional £3m to ‘accelerate climate adaptation work’.

This is an updated version of an article published on July 28, 2021.

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