Flooding is a naturally occurring process which cannot be prevented. In the UK, heavy rains are the most common cause of flooding. The UK has a history of flooding occurring when rivers receive more surface runoff water than they can cope with. Given the impact of climate change there is likely to be an increase in flood risk for some parts of the UK.
Flooding need not always be a problem. In some circumstances it is an important natural process which has beneficial impacts for biodiversity and soil health, for example. However, if it occurs in the wrong place a flood event can have significant negative economic and social impacts.
There are recent examples of lives being lost during a flood event (Dublin in October 2011 and Cumbria in 2009). Additional social and health costs of flooding have been identified especially for vulnerable sectors of society including the elderly, young, and single parent households. Flooding impacts directly on both physical and psychological health, and can cause problems including shock, gastrointestinal illnesses and respiratory illnesses. Psychological problems including acute stress, clinical depression and post-traumatic stress disorder have been recorded following various floods in the UK.
A flood event can have economic costs. Flooding can result in damage to businesses, in the form of lost output, stock damage or insurance claims and to homes through structural damage and destruction of possessions. Flooding can also cause substantial damage to agricultural land in terms of lost production, soil erosion and costs associated with removing debris and sediment from fields after a flood event. It is estimated that in the UK the annual flood damage cost is £1.1 billion.
The main drivers of flood risk and flood risk management have been identified as agricultural reform and land use policy and climate change.
The relationship between land use and flooding is complex. It depends on a variety of local factors including topography, soil structure, rainfall pattern and land use itself. In the agricultural landscape, several factors affect runoff generation, including the connectivity of flow paths, soil compaction and drainage efficiency. Agriculture can modify the scale and magnitude of flooding as it influences the timing and character of the delivery of water to the river. The impact that agriculture has on flooding can be seen throughout the world. For example it was shown that the increase in water fluxes in the Mississippi river between 1902 and 2008 were the result of an increase in agricultural discharge. Similarly, soil compaction and saturation in agricultural land were linked to the 2000 flooding in England.
There is a variety of evidence which indicates that intensive agriculture practices can affect hydrological processes and increase runoff and flooding. For example:
- loss of hedge rows and subsequent creation of larger fields (thus increasing slope lengths)
- cultivation practices (i.e. the use of heavy machinery or increased land stocking densities causing deeper compacted soils with reduced storage
- land use change from spring-planted to autumn-planted cereals which result in soil erosion
- cracks and mole drains feeding overland flow to drains and ditches
- intensive grazing and increase stocking densities, associated with decreased soil infiltration rate, porosity and hydraulic conductivity
The impacts of climate change are difficult to predict due to the complexities of flood generating responses and the inherent uncertainties within climate change predictions. However, much research shows that climate change is likely to increase flooding. The most recent IPCC report concluded that “the frequency of heavy precipitation events has increased over most land areas” and it is “very likely…that this will continue in the future”. Predictions from the Hadley Centre suggest drier summers and wetter winters with heavier and more frequent precipitation in Scotland.
Recent experience and predicted increases in flooding has led to a focus on flood risk management in the policy arena in recent years. A policy chain including the EU Water Framework Directive 2000, the Water Environment and Water Services (Scotland) Act 2003, the EU Floods Directive 2007, the Flood Risk Management (Scotland) Act 2009 and the Flood and Water Management Act 2010 has focussed on a more sustainable approach to flood risk management in the UK.
Sustainable flood management may be seen to have a number of components:
- legislation driven by good science, policy and planning;
- monitoring networks and warning systems;
- data for trend analysis and investigating flood generation processes;
- protecting, benefiting and involving communities;
- engineered flood protection schemes;
- natural flood management.
For more information contact: Wendy Kenyon