An unprecedented amount of rainfall fell across the UK last week, with many people left without power, a home and an answer to the question “why?”. It has been a stark reminder of how unprepared we are for tackling extreme weather events and will hopefully show local councils and the wider government the need to increase funding for environmental agencies and environmental engineering.

Although a miserable ordeal for those affected and an indictment of our governments ability to foresee the effects of natural disasters and listen to expert opinion, communities have been working hard to provide aid and comfort for one another.

Are the floods linked to climate change?

There are a few factors at play here, however the evidence is suggesting that yes, climate change has had an influence on the widespread flooding. To understand why, we must look at the processes and phenomena which drive such weather.

Greenhouse gases and their effect on temperature

You may be familiar with greenhouse gases (GHG’s) as they’ve been a hot topic of discussion for many years. They are an important part in keeping a temperature balance between the atmosphere and surface of the planet, however human activity is causing a positive feedback loop where more GHG’s are being added to the atmosphere faster than plants and oceans can fix and absorb them.

The main greenhouse gases:

  • Carbon Dioxide (Burning fossil fuels)
  • Methane (Agriculture)
  • Water Vapour
  • Ozone
  • Nitrous Oxide
Earth's_greenhouse_effect_(US_EPA,_2012)

Figure 1: Simplified greenhouse effect diagram

Some of the incoming solar radiation is absorbed by the surface and also by greenhouse gases in the atmosphere where it is re-emitted and distributed in all directions, as shown in Figure 1. The result is a rise in global atmospheric and surface temperature A.K.A the greenhouse effect.

The perfect conditions for extreme precipitation

What has this to do with flooding? The answer is that temperature controls how frequently it rains through natural processes called convection, evaporation and the merging of warm and cold air masses (including orographic). The warmer the air is, the more water vapour from evaporation is lifted up into the atmosphere through convection and can be stored, which later cools, condenses and falls as rain.

The United Kingdom has had one of the warmest winters on record, creating perfect conditions for an increase in moisture in the atmosphere. Theses conditions have been worsened by extra-tropical cyclones Storm Frank, Eva and Desmond which have brought a concentrated atmospheric river of moist air from over seas over areas of the UK increasing the amount of rainfall exponentially as the air becomes saturated and begins to cool.

Naturally more rainfall has been entering river channels and catchments where the excess water begins to overflow, spill and burst river banks. Areas located near rivers which don’t have much vegetation or woodland are more likely to flood due to poor soil structure where vegetation would prevent collapse and reduce the flow of water allowing time for it to be absorbed into the soil and root systems.

Inadequate drainage methods in urban areas where a lot of concrete exist has become evident, showing that underground pipes can’t transport water fast enough and lead to conditions worsening elsewhere in a catchment, often on the surface as the water can’t percolate (filter slowly) downwards through the impermeable concrete.

El-Nino

El-Nino is another factor affecting the extreme weather we’ve been seeing recently. Occurring at random intervals up to 7 years apart, El-Nino is a weather phenomenon caused by sea surface temperature changes in the tropical eastern pacific ocean. It has affected our weather by increasing surface temperatures, rainfall and wind storms. As the climate changes El-Nino is becoming more volatile and increasingly more difficult to predict, having the potential to devastate many developing countries which rely on El-Nino for agriculture and subsequently developed countries who are not prepared for such events.

Facing the reality of climate change

It is still uncertain whether climate change is to blame, however scientists have been running detailed models with results which suggest that climate change has increased the likelihood of floods by 40%. The study by Oxford University and the Royal Netherlands Meteorological Institute (KNMI) is yet to be peer-reviewed.

The reality is that we can expect in the coming years an increase in extreme weather and an increase in global atmospheric and surface temperatures regardless of our efforts to reduce GHG emissions which is not to say we should abandon them. The COP21 climate deal has at least shown leaders are thinking about climate change in regards to policies and regulations meaning next year it is up to us to pressure those who promised to produce more renewable energy projects and help ease out of the carbon economy.

On top of the deal, our government has promised an increase in spending on flood protection, albeit after the flooding occurred and a shortfall in funding for key flooding projects. Emergency council meetings should be under way to discuss flood planning with communities which are most likely to be affected, including talks on new and novel ways to combat extremes in weather like natural means of flood defences such as coppicing and permeable concrete.

As the year draws to a close, only action will tell how well we can deal with the worsening weather next year. We may have only witnessed the calm as more storms make their way through the UK, though we should remain hopeful that the government can learn from their mistakes and acknowledge that climate change will have severe socio-economic consequences.