Tuesday, 4 March 2014

Flooding 2014

It has been the wettest winter on record and one when the expertise of British Geological Survey staff was in high demand as flooding extended across much of southern England. At the same time we feel very sorry for those who have been and continue to be materially affected by the flooding and the impacts of the extremely wet ground.

The British Isles are located on the edge of the European tectonic plate system and this location has underpinned a number of our geographic and geological attributes. The one in play over the past few months is that we face the Atlantic Ocean and in particular, we are subject to the position of major geographical fluxes such as the atmospheric Jet Stream and also the  Atlantic Gulf Stream. The long term research that is ongoing and needed is to be able to better predict the weather patterns and in a given year, to allow people and government, to prepare for them. I note that at almost exactly the same period two years ago, BGS staff were advising government on the risks of a severe drought as we had not received enough rain over the two previous winters.

Some might feel that the British climate is just too difficult to forecast. I think we are making strides and there are indications that we know what triggers the trajectory of the Jet stream and observations on the Gulf Stream show some significant changes in warm water ocean flux that must link to our weather patterns (NERC Rapid Watch). How these fluxes are being affected by climate change is also an important line of research, as we know that the Earth is absorbing more heat, but we do not yet know how this links to climate change. We do know, for example, that the fluctuations associated with the El Niño/Southern Oscillation (ENSO) have favoured a cool La Niña phase in the past few years and when this shifts the planet will most likely accelerate into a warmer climate.

When the rain falls, it either evaporates, is taken up by vegetation, runs off or soaks into the ground.  It is this underground flow that is the research realm of our BGS groundwater scientists. A large amount of the flooding in the Thames valley and across southern England is related to groundwater flooding, where the ground is completely saturated, the underground aquifers are full and the gradients in topography result in groundwater emerging at the surface in places where it has never, or very infrequently, appeared before. Some streams in the chalk of southern England are flowing for the first time in living memory. Interestingly, even in a normal flow regime ~ 65% of the water in the Thames in London is sourced from groundwater and not surface water and it is groundwater that keeps many of our rivers flowing during the summer months.

Oxford Floods 2014 BGS (c) NERC

What can we do to help the people who are struggling and inform the government? We can provide estimates of how long flooding will continue, based on the predicted rainfall patterns and or knowledge of how our aquifers respond, and we can model where groundwater flooding will be the most serious, although that is of little help to those who's homes are already flooded. We can also help provide information on protecting important infrastructure and future planning. Because groundwater flooding has only relatively recently been recognised as a serious issue, there is only limited information on historical events and so it is as just as important that we invest in the research needed to improve our understanding of groundwater flooding and develop resilience as it is to be able to predict the weather.

High rainfall amounts and ground saturation and shallow groundwater flow also result in increased landslides and sinkhole risk. These commonly form in areas where clays or sand-rich sediments overly soluble rocks such as the Chalk or Gypsum. BGS has maps of areas most likely to be susceptible to landslides, underground solution features (sinkholes) or mobility of rocks. These help inform insurance and construction companies, but prediction of where an event might happen is extremely difficult especially in urbanised areas. In mountain ranges and rural areas it is possible to use ground measuring satellites coupled to systems in the ground  to measure movement and indeed some of the most threatening landslides and subsidence areas on the planet are monitored constantly.

BGS staff have worked hard in providing information to the public and government and also worked with the press in helping explain to the public how exceptional this particular flooding crisis is. We must however continue  to better prepare for the next crisis whether is from too much or too little rainfall input into our catchments.