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Flooding remains the most significant natural hazard worldwide. In the period 1985 – 2008 extreme rainfall events may have been responsible for USD 700 billion of damages. There is a general belief that such events will occur more frequently in the future due to climate change and changes in land use.
Flooding can be viewed as an environmental risk. Here, a flood event has a source such as an extreme rainfall event; waters with potential to cause flooding are conveyed through a pathway, the land surface and hydrological system; to a receptor, where flooding occurs. The risk of flooding to people and communities depends on the likelihood (probability) of a flood occurring and the consequences of the event when it does occur. The risk may be reduced by a combination of mitigation and adaptation. Mitigation refers to actions that seek to modify the source or pathway in order to reduce the probability of a flood occurring. Adaptation refers to actions taken to reduce the impact of flooding in receptor areas.
Although the largest share of economic flooding costs is borne by urban communities, agriculture occupies a large proportion of the landscape and has an important role to play in both flood mitigation and adaptation.
Agricultural land as a pathway
It is generally thought that the intensification of agriculture in the past five decades has resulted in greater and more rapid floods following extreme rainfall. Changing land management practices have reduced the infiltration capacity of the soil and drainage systems have been “improved” to evacuate water from agricultural land more quickly. Although there is little hydrological evidence to verify this relationship, it is generally felt that policies that encourage retention of water in the landscape can contribute to flood risk mitigation, especially for smaller, more frequent events. Practices such as (amongst others), low stocking rates, grazing management, low ground pressure tyres, and soil improvement measures can increase infiltration and reduce surface runoff. Measures such as contour ploughing, artificial bunding and retention ponds can slow down the rate of runoff from the land.
Agricultural land as a receptor
Agricultural land is often the receptor of flooding. The impact of flooding on agriculture varies considerably according to tolerance of the particular crop or land use activity to excess water, and the frequency, duration, depth and seasonality of the event. Where flooding is frequent, the use of the land may be limited to low productivity, flood resilient enterprises. Less frequent flooding may cause damage and losses to higher value land uses. If the likelihood of flooding is going to increase in the future, farmers will need to adapt by moving to more flood resistant or resilient enterprises and adopting measures to facilitate recovery after a flood event. These adaptations may also provide opportunities for parallel enhancements, such as biodiversity improvement through wetland re-creation and enhanced public access.
Flood water storage on agricultural land
National initiatives such as “Making Space for Water” (England & Wales) or “Room for Rivers” (the Netherlands), have encouraged a re-appraisal of land management options for floodplain areas. Agricultural land in washlands, polders and flood retention basins may be used for floodwater storage to mitigate flood risk elsewhere in the catchment. They provide opportunities to deliver multiple benefits, such as floodwater storage and enhancement of biodiversity and amenity, and potentially provide alternative sources of income for land managers.
Agricultural policy and flood risk
National policies for agricultural flood risk management in OECD countries have included a combination of mitigation and adaptation. Mitigation has mainly taken the form of public investments in flood defence and land drainage to support agricultural production. There have been few policies that directly mitigate flood generation from farmland, despite concerns that rural land use can contribute to flooding. Some features of agri-environment schemes now include components which are likely to reduce runoff. Furthermore, many policies that seek to influence agricultural land management in order to control diffuse pollution and soil erosion are also thought to have a beneficial impact on flood risk management. These policies typically adopt a non-regulatory approach, with emphasis on a mix of voluntary measures (such as agri-environment schemes), supported by economic incentives to farmers, with advice on improved environmental practices.
National policies include adaptation interventions that reduce vulnerability to flooding, mainly by providing flood warning systems, guidance on enhanced flood resilience, and emergency relief and compensation. Policies also include adaptation measures which seek to exploit potential synergy in the landscape. Examples include flood management and agri-environment initiatives that combine flood risk management, erosion control, biodiversity and agricultural livelihoods in floodplains. The creation of washlands and wetlands are examples of this.
Policy implications for the future
In future, given the prospect of increased flood probability associated with climate change, agricultural land is likely to play an important role in mitigation and adaptation strategies for flood risk management. Policies that are able to combine flood risk management with other objectives, such as, depending on priorities, nature conservation, the protection of natural resources and agricultural production and livelihoods, are likely to offer the best long term solutions. Where particular agricultural land management practices are known to result in serious flood risk, there may be a call for regulation and compliance with ‘good practice’. Where farmers purposefully manage land to retain and store potential floodwater to reduce flood risk for the benefit of others, there is scope for policies to reward them accordingly.
For the most part, agriculture’s role in flood mitigation and adaptation will be an adjunct to other flood risk management strategies, such as engineered flood defences for urban areas, rather than a complete substitute for them. The relative economic and environmental advantage of land management as an instrument of flood risk management depends very much on local, site-specific conditions, requiring careful assessment at the individual catchment scale. Given the uncertainties involved and the need to secure high standards of flood protection for urban areas in particular, it is unlikely that the management of rural and agricultural land can provide a complete solution for flood risk management. In some circumstances, however, it can make a significant contribution.