The beginning of 2014 has seen extensive flooding, predominantly in the south of England, due to a series of storms passing over the UK resulting in some of the largest rainfall totals seen on record: the wettest January since records began, twice the monthly average for January for Southern England with December and January being the wettest two-month period since records began (http://metofficenews.wordpress.com/2014/02/06/uks-exceptional-weather-in-context/).
The cause of the series of storms has been due to an unusually strong North Atlantic jet stream, resulting in a continual supply of moisture from the Atlantic over the UK causing the high rainfall totals. The cause of the strong North Atlantic jet stream is due to exceptionally cold weather in Canada and the USA and Pacific jet stream, caused by enhanced rainfall over Indonesia due to higher than normal ocean temperatures.
The effect of climate change will be for these events, and summer flash flooding, to become more frequent, which means that current methods of dealing with flooding, protecting homes in the event of a flood will not be enough. Fundamental changes into the design of homes, where homes are built and even accepting that current housing locations that are susceptible to flooding may need to be abandoned for more flood-resistant locations (http://www.theguardian.com/commentisfree/2014/feb/11/climate-change-flooding-engineer-somerset).
There have been many arguments about whether dredging the rivers would have prevented the current flooding, and whether it will reduce the probability of flooding in the future. It is important to realise that in the current situation the flooding is due to extreme rainfall, and not all of the flooding has been from rivers, e.g. ground-water flooding and storm-surges. Dredging is very costly and the benefit is unclear, e.g. to locations such as Somerset, and will not be a solution to many areas. Dredging isolated parts of a river will only move the problem further downstream; it is not a miracle cure to the current flooding crisis (http://www.theguardian.com/environment/2014/feb/12/flood-crisis-dredging-climate-change).
There are no quick fixes to the current flooding however the UK should be prepared for flooding to become more frequent. Once the current flood-water has disappeared will be the time when we should be remembering the flooding and looking towards long-term solutions to a problem that is going to become more frequent.
The UK has recently experienced two different types of flooding events. The first was coastal flooding caused by the low pressure of extra-tropical cyclone essentially pushing water from the sea into the rivers and along the coast. The second was caused by the prolonged rainfall associated with extra-tropical cyclones which have typically travelled across the Atlantic from the East coast of North America, picking up moisture which then falls as rain as the cyclones pass over land due to the presence of raised land. Both these events are more typical during the winter period (October – March) and last several days resulting in a lot of rain over this period. This leads to long periods of flooding (days) and typically over large areas, e.g. the whole of southern England.
The Flooding From Intense Rainfall (FFIR) programme is looking at the flooding that is caused by more short-lived events, such as convective storms that are more typical during the summer period (March – September), resulting in flooding that lasts hours and affecting a much smaller area. One of the most recent infamous examples of this was the flooding in Boscastle in August 2004 (http://www.metoffice.gov.uk/education/teens/case-studies/boscastle) which saw 75 mm of rain over 2 hours resulting in the destruction of houses, businesses as well as a significant economic impact. The summer 2007 floods that affected the whole of the UK were also due to short-lived intense rainfall events over a much wider area.
The difficulties faced when predicting these events is that they have a much smaller scale, typically less than 10s of kms, compared to the winter events which can have scales of 100s to 1000 kms. The timing and location of the rainfall is particularly difficult to predict and have a big impact on how well a specific catchment can cope – large catchments, e.g. the Thames can cope with a short intense rainfall event much more easily than a small catchment, e.g. the Valency which runs through Boscastle. To predict these events with greater accuracy a number of questions need to be addressed: 1) what are the atmospheric conditions that lead to these rainfall events, 2) how does the hydrology of each catchment vary and thus their ability to cope with such events, and 3) how do the different catchments respond to different rainfall intensities. These are the research questions of FFIR which is looking at catchments in the UK and their responses to surface water and flash floods.