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doi 10 1016j landusepol 2009 08 019 L H a b a A R A K W F W H m T m V o a o c r r m l U d a G 0 d Land Use Policy 26S (2009) S251–S264 Contents lists available at ScienceDirect Land Use Policy journa.

Land Use Policy 26S (2009) S251–S264 Contents lists available at ScienceDirect Land Use Policy journal homepage: www.elsevier.com/locate/landusepol Land use, water management and future flood riskଝ Howard Wheater a,∗ , Edward Evans b a b Department of Civil and Environmental Engineering, Imperial College, London SW7 2BU, United Kingdom Engineering Science, Oxford University, United Kingdom a r t i c l e i n f o Article history: Received 24 August 2009 Accepted 24 August 2009 Keywords: Water resources Flood risk Water quality a b s t r a c t Human activities have profoundly changed the land on which we live In particular, land use and land management change affect the hydrology that determines flood hazard, water resources (for human and environmental needs) and the transport and dilution of pollutants It is increasingly recognised that the management of land and water are inextricably linked (e.g Defra, 2004) “Historical context, state of the science and current management issues” section of this paper addresses the science underlying those linkages, for both rural and urban areas In “Historical context, state of the science and current management issues” section we discuss future drivers for change and their management implications Detailed analyses are available for flood risk, from the Foresight Future Flooding project (Evans et al., 2004a,b) and other recent studies, and so we use flooding as an exemplar, with a more limited treatment of water resource and water quality aspects Finally in “Science needs and developments” section we discuss science needs and likely progress This paper does not address the important topic of water demand except for some reference to the Environment Agency’s Water Resources Strategy for England and Wales (Environment Agency, 2009) © 2009 Queen’s Printer and Controller of HMSO Published by Elsevier Ltd All rights reserved Historical context, state of the science and current management issues The urban environment Urban development provides a useful illustration of some of the most obvious effects of land use change on water management Vegetated soils are replaced with impermeable surfaces, increasing overland flow and reducing infiltration, bypassing the natural storage and attenuation of the subsurface In addition, the conveyance of runoff to streams is modified Overland runoff is conventionally collected by piped storm-water drainage systems and conveyed rapidly to the nearest stream The result is a greater volume of runoff, discharging in a shorter time, potentially leading to dramatically increased flood peaks, but also reduced low flows and less groundwater recharge Urbanisation effects on fluvial floods The size of the effect of urban development on streamflow will depend on the natural response of the catchment The effects will be ଝ While the Government Office for Science commissioned this review, the views are those of the author(s), are independent of Government, and not constitute Government policy ∗ Corresponding author E-mail address: h.wheater@imperial.ac.uk (H Wheater) greatest where natural runoff is low, in catchments with permeable soils and geology, and can include changes in flood seasonality Natural catchments in the UK mainly flood after prolonged rainfall in winter, when soils are already wet and storm runoff is readily generated Urban catchments are not so seriously affected by these antecedent conditions and respond more rapidly to rainfall This means that intense summer rainfall may become a major cause of flooding (Institute of Hydrology, 1999) It is expected that the relative effects of urbanisation will reduce in larger, rarer floods, but current design guidance to quantify this is highly speculative For larger catchments, the effects are more complex, as the location of development within the catchment will affect its response For example, urban development located near to the outlet of a catchment may generate runoff before the main response of the natural catchment arrives The overall effect of urbanisation on the catchment flood peak will depend on the relative magnitude and timing of the constituent responses These effects have been well known for some 40 years (see e.g Hall, 1984), and to mitigate them, engineered solutions have routinely been adopted to reduce flood peaks through the provision of storage One common solution is the construction of a reservoir to provide “detention storage.” Crooks et al (2000) report on the effects of 30 years of urbanisation on two sub-catchments of the Thames, showing an apparent increase in flood frequency with urbanisation, followed by a reduction as storage solutions were implemented 0264-8377/$ – see front matter © 2009 Queen’s Printer and Controller of HMSO Published by Elsevier Ltd All rights reserved doi:10.1016/j.landusepol.2009.08.019 S252 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 There is much interest in Sustainable Urban Drainage Systems (SUDS) to manage urban runoff and associated problems of water quality Various design solutions can be implemented, for example restoring the infiltration of rainfall into the soil by directing storm runoff to engineered soakaways, or seeking to retard flows within the storm sewer system (Verworn, 2002) However, a lack of clear responsibilities for design and maintenance have limited uptake of SUDS in England and Wales The official review of the UK’s 2007 summer floods (Pitt, 2008) highlights the current problems of governance of water in the urban environment Pitt also comments on the increasing density of urbanisation He proposes solutions such as planning controls on paved areas within areas of domestic housing While well-developed design guidelines are available for conventional storage, based on a substantial body of research (Hall et al., 1993), the research base to support SUDS applications is much more limited There is no clear understanding of the effects of extreme rainfall on the performance of SUDS, and there is substantial anecdotal evidence that control of local-scale installations is ineffective, leading to errors in construction and defective operation (Packman, pers comm.) Urban stormwater flooding “Urbanisation effects on fluvial floods” section above addressed the effects of urban development on river flooding There are also major issues of flooding due to surface runoff within the urban environment This type of flooding is a major cause of insurance claims for flood damage Storm runoff is normally channelled via gully pots, into storm sewers, which are usually designed to accommodate relatively frequent events Under more extreme conditions, these sewers will start to surcharge (flow full under pressure), and as pressures build up, manhole covers can lift and the sewers discharge to the surface Such flows combine with surface runoff to generate flooding of roads and properties Urban flooding is often complex Sewer flooding can arise when pipes exceed their capacity, become blocked, have their capacity limited by river flooding, or a combination of these factors Divided management responsibilities are a problem in this area One of the recommendations of the Pitt report (2008) is for clear overall responsibility for urban flooding in England and Wales There are technical problems in urban flood design The frequency of surface flooding for storm sewers is not a design criterion, is often not known, and will vary greatly for different systems There has been a lack of technical capability to address this problem But in the past few years, models have been developed to represent the surface routing of overland flows, and associated storm sewer interactions, supported by high resolution topographic data, for example from LIDAR airborne remote sensing systems (Djordjevic´ et al., 2004) This offers exciting potential for a paradigm shift in the design of the urban environment to manage flood risk Floodplain development Finally in this discussion of urban flooding, we turn to issues of development on floodplains Many major towns and cities are adjacent to rivers, and there are continuing economic pressures to build in river floodplains However, floodplains have precisely the function that their name suggests; rivers can be expected naturally to flow beyond their banks every few years The natural functioning of a floodplain is to store and subsequently release flood waters, attenuating a flood as it travels downstream Over the past century or more, floodplains have been increasingly used for urban and agricultural development, and the need to protect that development has led to engineered disconnection of the river from its floodplain The result is a loss of flood attenuation, and increases in flood risk downstream This remains an issue of concern for the major European rivers such as the Rhine Levels of flood protection for some German cities have significantly decreased and active efforts have been made in recent years to recreate floodplain storage The same issues arise in the UK, although little work is available to quantify the effects of historic changes There is now interest in the UK in the potential for the return of floodplain land to an active water storage role, for example by reducing the level of flood protection of agricultural floodplain land (see below) Recent moves have been made by the UK Government to strengthen the role of the Environment Agency in the planning process in England and Wales (CLG, 2006), and also to raise awareness of planners of the risks of flooding A particular problem, highlighted by the 2007 floods, is the location of strategically important utility infrastructure in floodplains It is also not uncommon for emergency services, hospitals and residential homes for the elderly to be located in floodplains Water resource and water quality tissues Towns and cities need water supplies, which are often imported from other catchment areas After use, this water is conventionally routed through the sewer system, treated, and discharged to the local river Urbanisation reduces natural water infiltration into soil, so that in urban rivers, effluent discharge may be a dominant component of river flows, particularly under the low flow conditions of summer The release of treated effluents to streams has long been a major source of pollution, and nutrients have been a particular concern EU legislation, in the form of the Urban Wastewater Treatment Directive, has required major treatment works to introduce tertiary treatment to reduce nutrient loads, but this requirement does not extend to the large numbers of small treatment facilities Jarvie et al (2007) report observations of phosphorus in the river Lambourn in Berkshire These measurements show the effect of sewage effluent on phosphorus loads in the river, the reduction in phosphorus when treatment was improved, and the subsequent release of phosphorus from river sediments as the system re-equilibriated In addition to the discharge of treated effluents, there is potential for pollution from urban storm runoff, which can include oils and heavy metals Urban storm drainage systems normally include simple devices, such as gully pots, to collect sediments and associated pollutants, while one of the roles of SUDS, discussed above, is to reduce pollutant discharge Particular problems arise where storm and foul sewers are combined Under extreme flows, treatment facilities are unable to accept the storm discharges, and overflows of sewage effluent to watercourses can occur This is a concern for pollution of the Thames in London, and is one of the motivations for major investment in a new interceptor sewer There is also scope in urban areas for a wide range of pollutants to be released to the water environment from accidents, spillages, broken pipes and illegal activities In recent years, industrial pollution of surface water systems in the UK has been greatly reduced in response to tighter regulatory controls But in the subsurface, there is a legacy of pollution of soils and groundwater, with long-term consequences Groundwater in urban environments is commonly polluted and is not suitable as a potable resource The management of water in the urban environment can significantly modify hydrological impacts The harvesting of rainwater from roofs can reduce both storm runoff and the demand for other water resources, while the re-use of so-called ‘grey water’ at a domestic scale is technically feasible, although not currently economic (Liu et al., 2007) Vegetation can be used to attenuate and reduce runoff and associated pollution, either at the scale of ‘Green Roofs’ or in larger scale implementation of SUDS In water-limited areas, the management of urban water has been intensified, and H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 associated investment has been made to reduce pollutant loading In Singapore, for example, runoff is collected as a resource from approximately 50 per cent of urban areas, and wastewater is treated to create ‘NewWater’, mainly for industry, but in part for domestic supply Changes in water management can have important effects In London, a large lowering of groundwater levels occurred due to industrial water use after the industrial revolution In recent years, that use has reduced, and rising groundwater levels have posed major problems for subsurface infrastructure, including basements and the underground rail system Pumping is a solution, but due to historical pollution, the water that it produces is not suitable for water supply The mismanagement of water can also have significant impacts Leaking water distribution systems provide a source of water to the subsurface, and leaking sewer systems are a source of pollution A striking example is in Riyadh, Saudi Arabia, where the leakage of imported water has created major problems of rising groundwater, and perennial flows in the once ephemeral Wadi Hanifah The rural environment Afforestation While urbanisation is a dramatic change to the natural environment, the effects of other land use changes are more subtle The first long-term experimental hydrological research programme in the UK, based initially on the Plynlimon catchments in Wales (Hudson and Gilman, 1993), was initiated some 40 years ago in response to concerns for the effects of afforestation on water resources This research showed that high rates of evaporation of interception storage (water wetting the surface of leaves) had important effects on the water balance This finding was consistent with a large body of international literature which shows that in the long term, afforestation reduces flows due to increased evaporation (Bosch and Hewlett, 1982) However, there has been some ambiguity about the effects of lowland broad leaf forests, with contrasting views put forward (Calder, 2007; Roberts and Rosier, 2005) Although long-term effects are relatively well defined, in the short and medium term, effects on flows may be very different Studies by Robinson (1986) show that the drainage practices widely used at that time to establish forests in the UK uplands gave rise to an increase in storm runoff, an effect that may last for many years Field drainage In the 1970s, attention in the UK turned to the effects of agricultural drainage on flooding (Robinson and Rycroft, 1999; Robinson, 1990) Under-draining, the use of underground pipe systems to drain soils to improve production, is a common agricultural practice and the UK is one of the most extensively under-drained countries in Europe Much of this drainage occurred between the 1940s and the 1980s, encouraged by government grants (Robinson and Armstrong, 1988) In the UK, very low-permeability soils often have a secondary treatment such as ‘subsoiling’ or ‘moling’, to improve the flow of water to the drains Although the cessation of grants in 1984 has meant that there has been little new land being drained, existing drainage is still maintained to varying degrees (Armstrong and Harris, 1996) The installation of field drains will generally cause a reduction in surface and near-surface runoff due to a lowering of the water table and an increase in the available storage capacity of the soil However, runoff from drained land may be faster or slower than from undrained land depending on the nature of the soil and its management (Armstrong and Harris, 1996), as well as the timing and intensity of rainfall Reid and Parkinson (1984) illustrated how runoff response from drained fields varied seasonally, depending on antecedent moisture conditions A reduction in the time to S253 peak flow and an increase in the magnitude of peak flows has been reported in relation to installation of field drains in a 16 km2 clay catchment in North East England (Robinson et al., 1985) The drainage of soils rich in organic matter may have both short and long-term effects Lowering the water table in peatlands will increase the amount of available storage capacity in the short term but will also increase organic matter decomposition rates, resulting in a subsequent decrease in available storage as the organic matter content decreases (Holden et al., 2004) and hence potentially an increase in flood peaks in the long term, as well as long-term soil damage Agricultural intensification The floods that have affected England and Wales since 2000 have reinforced more general concerns that changing agricultural practices in the UK may have increased the risk of flooding (Wheater, 2006) This is not an issue solely confined to the UK and similar concerns have been raised elsewhere across northern Europe (Evrard et al., 2007; Pinter et al., 2006; Bronstert et al., 2002; Pfister et al., 2004; Savenije HHG, 1995) Prior to World War II, the UK agricultural landscape was characterised by small fields with dense hedgerows and natural meandering rivers The subsequent drive for increased productivity in farming brought about major changes (O’Connell et al., 2007) These include the loss of hedgerows and an increase in field size, the installation of land drains connecting hilltop to river channel, and channelised rivers with no riparian zone This landscape change has been accompanied by changing patterns of agricultural land use and the intensification of production, although recent changes in agricultural policy have led to some de-intensification in the past few years Changes in arable production have been associated with changes in cropping and land cultivation practice and the increasing use of heavy machinery There have been pressures to work land when soil moisture conditions are unsuitable, and to work land unsuitable for purpose In the uplands, the source areas for the UK’s major rivers, land use is dominated by grassland production, mainly for sheep In Wales, 72 per cent of agricultural land was estimated to be under grassland production in 2005, almost exclusively to support sheep farming Sheep numbers in Great Britain doubled between 1950 and 1990 as a result of farm support payments based on stock numbers (Fuller and Gough, 1999) Associated with this change has been an increase in the amount of improved pasture in upland areas, which has been created by draining, ploughing, and reseeding, also financially supported by government and EU incentives (James and Alexander, 1998) These increased numbers also led to the use of less suitable land for grazing, supporting higher stock intensities on marginal land The degradation of soil structure, due to either arable or grazing intensification, can lead to reduction in soil infiltration rates and available storage capacities, increasing rapid runoff in the form of overland flow (e.g Heathwaite et al., 1990; Bronstert et al., 2002; Carroll et al., 2004; O’Connell et al., 2004) There are concerns in the UK and elsewhere in Northern Europe that this may increase the risk of flooding (Holman et al., 2003; Stevens et al., 2002; Boardman et al., 1994; Burt, 2001) However, the role of land use management in enhancing or ameliorating UK flood risk has been identified as an unanswered question in a major review commissioned by Defra (O’Connell et al., 2004) The research cited above mainly focuses on the role of land management intensification at the scale of individual fields The catchment-scale effects remain largely unresolved Beven et al (2008) attempted to identify the catchment-scale effects of land use and land management change by interrogation of catchment-scale data, but failed to identify a clear relationship between land use and land management and river flows This does S254 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 not mean that such a relationship does not exist, but rather that errors in catchment-scale measurements and the multi-faceted nature of catchment change, combined with climate variability, not allow such effects to be detected, although they may be substantial A recent multi-scale experimental and modelling study has been established at Pontbren, in mid-Wales, to provide data and models to address this issue (Marshall et al., 2009; Jackson et al., 2008; Wheater et al., 2008a,b) The soils at Pontbren mainly comprise heavy clay, with a history of land drainage, and are predominantly grazed by sheep Pontbren’s land management background is also noteworthy From the 1970s to the 1990s, sheep numbers increased by a factor of six, and animal weights doubled Since that time, farmers have reduced stocking densities, moved to smaller and hardier breeds, and started reinstating hedgerows and shelter belts Experimental studies have shown rapid improvement in soil structure and permeability associated with the establishment of tree shelter belts, and modelling studies have been used to investigate both field and small catchment-scale effects While runoff volumes are not significantly changed by the planting of shelter belts, important changes to runoff peaks are indicated Simulations suggest that for frequent events, the median effect of reverting to 1990s patterns of land use would be to increase flood peaks by 13 per cent Conversely, introducing optimally placed tree shelter belts to the current land use would reduce peak flow by 29 per cent, and introducing full woodland cover would reduce flows by 50 per cent Considering an extreme event, the corresponding median effects are a per cent increase and a per cent and 36 per cent reduction, respectively While some of these effects are not large, neither are they insignificant It is worth noting that such intervention measures also have benefits for diffuse pollution and for wildlife habitats, but there is currently no framework for integrated assessment of these possible benefits The above discussion has related to the generation of runoff from fields and hillslopes, i.e the amount and timing of water entering rivers The routing of flows down rivers is affected by floodplain management As we have seen in “Floodplain development” section, there has been a disconnection of rivers from their floodplains, itself associated with the provision of increased flood protection for agricultural land But it is possible to reduce flood risk downstream by reducing the level of protection for agricultural land in floodplains, and allowing the natural storage and attenuation of water associated with floodplain inundation to be re-established However, issues are not straightforward; agricultural areas with flood defences can act as washlands in high flows, storing water above its natural level and reducing the peaks of flood hydrographs Hence removing the surrounding flood protection banks entirely may in some cases perversely increase flood risk to downstream areas In addition, there are social and economic issues associated with their removal, for example with compensation payments paid to landowners rather than tenants Water quality, sediments, geomorphology and habitats The flow regime of a catchment, in combination with its sources of sediment supply, determines the geomorphological behaviour of a river This means that land management practices have implications for suspended sediments, river geometry and bedform This has implications for habitats and infrastructure Defra (2008) states that up to 75 per cent of sediment loading to rivers can be attributed to agriculture Collins et al (1997) analyse sediments on the Upper Severn and note the signature of accelerated erosion of soils due to afforestation and deforestation and the erosion of pasture soils Hatfield et al (2008) analysed sedimentation rates in NW England Pulses of erosion and sediment flux were associated with mining and deforestation in the 19th century, agricultural intensification in the mid-20th century, and a recent possible signal of climate change Henshaw and Thorne (2008) report significant increases in sediment bed-load when comparing improved and unimproved pasture at Pontbren Major stream incision has taken place in areas of improved pasture Field ditches, gullies and over-steepened banks provide sources of coarse sediment These authors also identify a recent reduction in bed-load yields, possibly associated with measures taken by the farmers to protect banks from cattle and reinstate hedgerows and woodland shelter belts Land management is also strongly associated with chemical water quality The major pollutants of concern for the UK are nutrients, particularly nitrate and phosphates Defra (2008) estimates that 60 per cent of nitrate pollution and 25 per cent of phosphates in English waters originates from agriculture In response to the EU Nitrates Directive (1991), controls are placed on agriculture through the designation of Nitrate Vulnerable Zones (NVZs), which have recently been revised for England, increasing the area designated from 50 per cent to 70 per cent This means that in most of England and Wales, limits are imposed on the permissible loading of organic and inorganic nitrogen applications, and on their timing, and no application is allowed on areas defined as being at high risk of runoff There are important tensions between agriculture and water quality, and these raise associated policy issues Lovett et al (2006) demonstrate that nutrient standards in the River Slea could only be met by taking substantial areas of land out of agricultural production An overarching issue is where the responsibility for nitrate pollution should lie Lovett et al (2006) also provide an economic analysis that indicates that the cost of nitrate reduction in agricultural production is four times that of nitrate removal by treatment of the potable water supply Similar issues apply to phosphorus In a modelling study of the potential impacts of phosphorus management on the rivers of eastern England, Wheater and Daldorph (2003) conclude that while constraints on agricultural management can reduce river concentrations significantly, it would be hugely expensive to achieve the low levels of phosphorus concentration associated with good ecological status Relatively little attention has been paid to biological water quality, although faecal indicator fluxes are of concern Hunter et al (1999) show the effects of sheep grazing on faecal bacteria levels in an upland environment in England, and Oliver et al (2005) show significant E coli loads in runoff from land grazed by cattle and treated with livestock wastes Crowther et al (2002) demonstrate the effects of lowland pastoral agriculture on coliform, E coli and Streptococci concentrations on river waters and hence on marine bathing water quality But Kay et al (2005), in an analysis of the 1600 km2 Ribble catchment in NW England, concluded that urban areas were the dominant source of faecal indicators for that catchment Many other pollutants are relevant to the rural environment, but space precludes their detailed treatment here Some are of local concern (e.g pollution from sheep dips), others reflect specific incidents (e.g disposal of carcasses in the Foot and Mouth epidemic) and some are widespread and may reflect long-range pollution (e.g acid deposition, which is dependent on land cover) A principal driver for water resources management is the EU Water Framework Directive This focuses on ecological quality and is a driver for the protection of water quality and of aquatic habitats It involves a timetable for the achievement of environmental targets However, particular issues arise with respect to groundwater and groundwater-dominated rivers, such as the chalk streams of South East England Chalk groundwater is recharged by water travelling through an unsaturated zone that can be up to 100 m deep Recent research has addressed uncertainties in H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 S255 Fig The flooding system Upper image: the fluvial/coastal flooding system Lower image: the intra-urban flooding system (from Evans et al., 2004a,b) the transport of nitrate in this unsaturated zone, confirming that rates of movement are of the order of m per year This means that a legacy of decades of nitrate history is moving slowly to groundwater—the so-called ‘nutrient time-bomb.’ (Jackson et al., 2007) Land use futures: a water management perspective The relationship between land use and flooding was explored in the 2004 Foresight Future Flooding project (Evans et al., 2004a,b), which was recently revised as part of the Pitt Review of 2007 floods S256 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 Fig Combined climate change and socio-economic futures used in the Foresight 2004 analysis (Pitt, 2008; Evans et al., 2008) We first summarise key issues from these reviews, and then discuss the water resource and water quality perspectives Future magnitude, distribution and drivers of flood risk in England and Wales The aim of the 2004 Foresight Future Flooding project was to use the best available science to provide a challenging vision for flood and coastal defence in the UK between 2030 and 2100 and so inform long-term policy It employed two forms of analysis—a quantitative, probabilistic, computer analysis using very large Geographical Information System (GIS) databases based on the Risk Assessment for System Planning (RASP) system developed by the Environment Agency, and a qualitative analysis The latter used a structured method to draw out evidence-based expert knowledge to estimate approximately how big an impact the various drivers and responses might have on flood risk under different future scenarios, and then ranked them in order of impact on flood risk The project saw the flooding system as being composed of two sub-systems, the catchment and coastal flooding system, and the ‘intra-urban’ system, where flooding arises from events within urban areas This is in contrast to river and coastal flooding, where water enters urban areas from outside (Fig 1) The analysis used four combinations of climate and socioeconomic scenarios to create alternative pictures of possible futures (Fig 2), drawing on UKCIP02 and the Foresight Futures socio-economic scenarios (SPRU et al (1999); OST 2002) uing to spend the same amount of money and following the same policies as in 2004 The results of this were striking, with flood risk increasing in the 2080s under all four scenarios, as illustrated in Tables and The distribution of flood risk was shown by maps such as those in Fig 3, which compared the present and future distributions of economic damage The concentration of flood risk around the coast and in the major urban areas is obvious, as is the lesser severity of future flood risk under the Global Sustainability scenario compared with the high-growth, high climate change, low-regulation World Markets scenario It should of course be borne in mind that UK government expenditure on flood risk management has increased considerably since the publication of the Future Flooding report in 2004, thereby reducing the growth of future risk under the ‘business as usual’ scenario Nevertheless the flood risk multipliers and the distributions of future flood risk shown in Fig remain of interest in showing the potential for flood risk to increase in the future Drivers of future flood risk What then were the drivers of these large increases in future flood risk? Here we draw on the Pitt Review update of the original qualitative analysis, which grouped the drivers according to a Source/Pathway/Receptor (SPR) classification as shown below in Table 3: The top 12 drivers, graded by national flood risk multiplier in the 2080s, are shown in Table 4: It can be seen that while climate change drivers feature highly, many drivers connected to land use are also prominent including infrastructure, buildings and contents, urbanisation and intraurban runoff In addition, the flood risk created by climate change is dependent not only on the increased frequency of flooding, but also on the distribution and number of receptor assets in the floodplain, a function of the degree of regulation under the different scenarios in Table The Future Flooding analyses went on to show that with portfolios of structural and non-structural responses, implemented in a sustainable way, the future risks could be pulled back to a level around that of the present day The top 12 responses are shown below It can be seen that responses related to land use rank alongside engineering responses as the most powerful in controlling future flood risk Land use and the drivers of future flood risk Magnitude and distribution of potential future flood risk The quantitative analysis was first run under a ‘business as usual’ assumption for flood risk management, with government contin- We now examine more closely some of the flood risk drivers and responses in the context of land use Table Flood risks expressed as Expected Annual Damage (EAD) and the baseline costs of flood defence for the business as usual option—catchment and coastal, 2080s Present day Baseline case, EAD£ million/year Baseline cost £ million/year 1040 500 World markets 20,500 500 National enterprise 15,100 500 Local stewardship Global sustainability 1500 500 4860 500 Table Flood risks expressed as Expected Annual Damage (EAD) and the baseline costs of flood defence for the business as usual option—intra-urban, 2080s Baseline case, EAD£ million/year Baseline cost £ million/year Present day World markets National enterprise Local stewardship Global sustainability 270 320 7830 320 5060 320 740 320 1570 320 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 Fig Foresight futures: comparative risk – Expected Annual Damage – residential and commercial properties, 2080s S257 S258 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 Table Combined list of fluvial/coastal and intra-urban drivers Driver group Driver SPR classification Climate change Precipitation Temperature Relative sea-level rise Waves Surges S S S S S Catchment runoff Urbanisation Rural land management P P Groundwater systems and processes Groundwater flooding P Fluvial systems and processes Environmental regulation River morphology and sediment supply River vegetation and conveyance Urbanisation and Intra-urban Runoff P P P P Urban systems and processes Sewer conveyance blockage and sedimentation Impact of external flooding on intra-urban drainage systems Intra-urban asset deterioration P P P Coastal processes Coastal morphology and sediment supply P Human behaviour Stakeholder behaviour P Socio-economics (now includes rural and intra-urban receptors and all types of flooding: river, coastal, pluvial and coincident) Buildings and contents Urban impacts Infrastructure impacts Agricultural impacts Social impacts Science and technology R R R R R R Climate change drivers The high ranking of coastal drivers draws attention to their importance and to the choices which must be made between providing high levels of funding to resist rising coastal threats, realigning defences, or abandoning large tracts of land to the sea The connection between land use in coastal areas and future flood risk is obvious Table National ranking of drivers, graded by national flood risk multiplier—2080s Precipitation is a pervasive driver for non-coastal flood risk Although future precipitation is highly uncertain, increased frequency of extreme events is expected This raises concerns for consequential impacts including intra-urban, fluvial and groundwater flooding Increased flood risk for urban and rural areas will impact on lives, infrastructure, agricultural production and ecosystems, while increased floodplain flows have implications H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 S259 Table Response rankings for the 2080s for land use management The possibility of having to find the space through our riverside towns and cities to accommodate flood flows up to 40 per cent greater than today’s values presents great challenges not only in engineering terms but particularly to urban planning It contrasts awkwardly with Government policy of reusing brownfield sites Many of these originated as waterside developments during the industrial revolution, using water as a source of power and transport Increased flooding will also impact on the role of agricultural land management in flood mitigation, as well as affecting agricultural land and productivity Managed realignment is often seen as a solution to coastal flood and erosion defence problems However, the cost effectiveness of this measure may be less than was believed (Rupp-Armstrong, 2008) and it may not be as widely adopted as originally envisaged Two factors have a bearing here The first is the increasing cost of managed realignment schemes The second is the rising value of agricultural land in the UK and the greater awareness of food security as an issue due to climate change and changing world markets (Brown and Funk, 2008; IAASTD, 2008) Although less than per cent of flood damage affects the agricultural sector (Evans et al., 2004a,b), a large proportion of the most agriculturally productive land in England and Wales is dependent on flood protection and land drainage All the scenarios in our 2004 report reveal high exposure to flood risk in the Fens of East Anglia The increased importance now being placed on future food security may require response options to be re-evaluated to reduce flood risk and to maintain standards of land drainage in areas of national agricultural importance Urbanisation Urbanisation acts as a driver of flood risk by increasing runoff which affects communities downstream, and by increasing the assets at risk of flooding The effects of urbanisation on runoff are well known Without mitigation, urbanisation increases flood risk The key issue is the extent to which mitigation measures are implemented, either at catchment or local scale (see below) So the effect of this driver is heavily dependent on socio-economic scenarios Urban areas are also impacted by floods, a process exacerbated by population growth, household distribution and human attitudes and desires Development on floodplains is of great concern It puts property and infrastructure at risk of flooding, and affects the transmission of floodplain flows The Pitt Review (Pitt, 2008) shows vividly that a number of recently constructed housing estates were flooded in 2007 Decisions on where to build houses, factories and other infrastructure are now recognised as a key tool in managing future flood risks The importance of protecting vital infrastructure from flooding is also clear However, this issue is not a simple one The 2004 Foresight flooding reports (Evans et al., 2004a,b) drew attention to the need to balance flood management against other economic, social and environmental needs, especially the demand for new housing It would be controversial to ban redevelopment of brownfield sites that lie in the floodplain, but are behind well-managed flood defences affording a high standard of protection This applies to much of London The need is perhaps for more sharply targeted policy instruments Future urban flood risk will be affected by changes in the way in which urban areas are managed, their characteristics, and how planning and management change in the context of social and climate change Important effects here may include the renewal of existing urban spaces, new urban forms, new densities of development, more green space, and encroachment into green belts While changes in existing urban form are certain to occur, the fabric of urban areas changes relatively slowly in the UK For example, the current rate of replacement of the housing stock is 0.1 per cent per S260 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 annum and the rate of addition to that stock is per cent In addition, 22 per cent of all land in England is already in some urban usage and there is limited scope for further urban expansion This limitation is compounded under some scenarios used in the Foresight Future Flooding project which suggest that the UK could be short of agricultural land for food production A significant percentage of insurance claims for flood damage originate from outside of the floodplain They arise from the presence of groundwater, local flooding in the form of ‘muddy floods’ (runoff from nearby hills and fields), and from intra-urban flooding Urban drainage systems and processes As we noted in “Historical context, state of the science and current management issues” section, a number of drivers connected with the urban drainage system also are of relevance to urban land use via their interaction with the form and function of the urban area, and are likely to become a more important factor in limiting flood risk in the future Building development, operation and form include opportunities to manage local flood risk though actions taken at the building level Examples include the use of permeable surfacing in car parks and rainwater harvesting Responses from the various stakeholders are also included (i.e individual behaviour) together with responses that relate to actions when flooding does occur (mitigation) However, even where there is control over urbanisation, ‘creep’ adds hard surfaces in an uncontrolled and unpredictable manner Source controls comprise a range of possibilities Classical solutions to increased flood risk include construction of storage reservoirs to attenuate flows More recent methods focus on SUDS, although lack of clear responsibilities has limited their uptake in England and Wales The 2008 Pitt Review also highlights increasing density of urbanisation—proposing controls on paved areas within domestic housing, for example Rural land management As was the case for urban water management, rural land has a role both as a driver of flood risk, and a receptor The role of rural land management in flood runoff generation has been discussed above Although there has been some de-intensification of agriculture in recent years, this followed dramatic intensification of UK agriculture over the previous 30 years, in response to agricultural policy and economic and social pressures It is thought that this intensification has increased runoff generation at the local and small catchment scales, and a significant proportion of UK soils are classed as degraded Clearly the opportunity exists for land management to mitigate flood risk, both in the context of runoff generation, and by the potential use of agricultural floodplain land for flood storage and attenuation (Morris et al., 2005) Such intervention measures also have benefits for diffuse pollution and for wildlife habitats, as we noted above, but there is currently no framework for the integrated assessment of these benefits There is also a growing perception that changes in peri-urban land use and land management may have a significant impact on flood risk Agricultural intensification, together with additional urbanisation of the peri-urban area, has produced significant changes in the volumes of runoff that enter the urban area from the peri-urban area, including the effects of reduced infiltration and increased overland flow Farm land is more tolerant of flooding than urban land, and the unit costs of damage are much lower there While flooding and soil waterlogging in some intensively farmed areas can result in significant losses of agricultural output, in others this is not the case Changing polices towards agriculture and environment suggest there could be benefit in ‘setting back’ some previous agricultural flood defences to restore ‘natural’ floodplains in ways which provide benefits in terms of flood storage and enhanced biodiversity Promoted by financial rewards to land managers, these measures could support rural livelihoods With respect to the alternative futures explored in the Foresight Future Flooding project, the constituents of the driver set (Table 4) are mainly ranked as having a medium impact on future flood risk, although the impact of urban and rural land use is perceived to be particularly high for the utilitarian world market and national enterprise scenarios Agriculture is shown to exert a medium influence as a receptor under most scenarios The reason for this assessment varies between scenarios due to differences in land use, damage costs, and the degree of exposure to flooding For rural land use as a pathway and a receptor, flood risk is mainly a function of societal preferences evident in agricultural and environmental policy drivers Similarly, the contribution of urbanisation to flood risk is influenced by socio-economic factors which shape the nature and rate of urban development Land use, water resources and water quality Future flooding in the UK has received considerable attention, with extensive scenario definition and analysis undertaken in two Foresight studies But other aspects of water management futures are less well developed Water resources for the future For England and Wales, an Environment Agency, 2001 report on Water Resources for the Future (Environment Agency, 2001) gave projections of water demand under a number of scenarios similar to those used by Foresight Future Flooding This has recently been updated, with a 2009 report on the Water Resources Strategy for England and Wales (Environment Agency, 2009) The problem of the provision of water is compounded by the fact that precipitation is biased towards the North and West of Britain whereas population and hence consumption are biased towards the South and East The current water resources status shows relatively large areas of the South East as either overabstracted or over-licensed, and the scenario adopted for 2050s climate shows reductions in mean monthly Summer and Autumn river flows of up to 80 per cent Scenarios are used to support projections of future demand on the basis of variables including population growth They suggest changes by 2050 ranging from a 35 per cent increase for ‘uncontrolled demand’ to a 15 per cent reduction for ‘sustainable behaviour’ One possible growth area is water use for irrigation At the moment this accounts for only 1–2 per cent of water use, although this demand is naturally at its peak at times and in areas of water shortage Use of water for irrigation could rise by 25 per cent by 2020, and given the large changes in growing conditions projected for the 2050s (see Fig 4), could be much higher by then However, water resource futures are highly uncertain The Environment Agency report (2009) points out that more than 60 per cent of water consumed in food and goods and services used is imported, so the UK economy is particularly vulnerable to global water scarcity Although the provision of extra water is a challenge, proposals such as storing more water in mid-Wales and transferring it eastwards to the Thames basin and beyond are under active study (Thames Water, 2009) The problems of realising such transfers are several They include the current structure of the water industry in England and Wales, funding, the environmental impacts of different water quality levels, and the possibility of invasive species H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 S261 Fig Potential changes in summer growing conditions (after EA, 2009) It also raises local, rather than national, land use issues, because new reservoirs would be needed But the report said that contributions to solving the water supply problem might come in part from more efficient water use in the home, in industry and in agriculture Looking to the 2050s, more radical futures for water resources seem plausible, particularly in South East England These would have implications for urban and rural land use In addition to the obvious target of leakage reduction, water management in the urban environment could plausibly include rainwater harvesting, water re-use and the use of controls such as green roofs, which have benefits in terms of reduced flood runoff and reduced demand for public water supply Rural land management will depend heavily on land use policy and socio-economic factors, and the future of agricultural land use appears particularly uncertain at the present time Scarcity of food in world markets could lead to a re-emphasis on UK food production In combination with change in the UK climate, this could lead to significantly increased demand for water from the agricultural sector Apart from irrigation issues, water-related implications of climate change for future land use remain relatively unexplored The Environment Agency (2009) notes that “If land use changes S262 H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 significantly in some locations, our work has shown that it can change the amount of water that makes its way to the water environment.” This report notes the potential for the greening of urban areas to limit the increases in temperature which are implied by predicted climate change This greening is identified as another source of demand for water, but the report may underestimate its scale In current urban desert environments, domestic water use is extremely large—some 870 l per person per day in Phoenix, Arizona (Gober, in press), mainly for outdoor use This compares to the Environment Agency target for the UK of 150 l per person per day The same authors note that “clearly on a larger scale, afforestation, or a change in land use to deep-rooted biomass crops could adversely affect water resources, or a move to crops with lower water intensive requirements could have a benefit.” Current EU legislation, as we have noted, emphasises the protection of ecological quality, and this aspect of land management will undoubtedly need reconsideration in the light of climate change There is little sense in protecting unsustainable ecosystems Much research will be required to develop appropriate strategies for habitat protection and management, given the magnitude of the changes to climate and the water environment that are foreseen by the 2050s Interactions between land use and water quality can also be foreseen, although as yet they remain relatively unexplored Obvious issues concern future policy for diffuse pollution, given changes to the water flows available to transport and dilute nitrate fertilizers, and changes to the intensity of storms that will change the mobilisation of phosphorus These depend on changes to soils and vegetation which are as yet unquantified Emerging issues include the transport of organic carbon from organic upland soils This is of concern to the water industry because it can introduce colour and by-products to water This raises the more general issue of catchment carbon budgets, and the integrated management of land and water to maintain carbon stores as an ecosystem service Science needs and developments Rural land use and flooding The prediction of the hydrological impacts of rural land use change remains a challenging research question (Wheater, 2002; O’Connell et al., 2007) Few land use manipulation studies include the extensive monitoring necessary to define the effects on runoff processes at local scale adequately, and there is a multi-scale modelling problem of upscaling to represent impacts at catchment scale While new methods have recently been developed to represent the effects of changing soil properties and vegetation for upland land management (Jackson et al., 2008; Wheater et al., 2008a,b), they have been supported only by a single extensive experimental data set Current research is intended to generalise these modelling tools for a wide range of land use issues, but the results will be subject to high uncertainty without more extensive data At the local scale, new technology for detailed digital elevation mapping of urban areas has provided support for new simulation tools for urban flood management Prototypes are available now to represent the interaction between sewer flows and surface flooding, and hence to support new approaches to intra-urban flood risk assessment and the design and management of urban infrastructure Land use and water quality A further set of fundamental research questions concerns the impacts of rural land management on water quality, and specifically diffuse agricultural pollution For example, the processes governing the nitrogen cycle in soils are extremely complex They can be represented in simplified process-based models (e.g INCA, Wade et al., 2002), but the data to support the selection of appropriate parameter values is limited, as is the information available to specify past inputs This means that attempts to synthesise catchment response are typically based on subjective judgement, and are subject to high uncertainty The complexity of the models is such that inverse modelling will lead to high levels of parameter uncertainty (e.g McIntyre et al., 2005) The approach adopted by the Environment Agency to determine NVZs is based on a combination of modelling results and observed nutrient concentrations, but with the data being given greater weight where it is available An alternative approach is to ignore process complexity and use simple data mining Thus in the case of phosphorus, ‘export coefficients’ have been defined from observed data to estimate annual catchment-scale phosphorus exports Johnes (1996) These can be used to constrain dynamic models, as demonstrated by Wheater and Daldorph (2003) It is likely that progress in all of the issues of rural land management discussed thus far will depend on the maximum use of process understanding and data, combined with catchment-scale observations In the urban environment, water quality issues remain particularly challenging A wide range of pollution is possible, including for example, road runoff, accidental spills, leaking sewers, leaking industrial facilities, and leaking petrol station storage tanks And there is often a long-term legacy of pollution in soils and groundwater, for example from the history of town gas production in the 19th and 20th centuries There is a need for more extensive data to quantify these pollution problems, but specific issues are likely to need intensive forensic investigation Particular problems arise for groundwater-dominated catchments For example, Jackson et al (2006) developed a new model to represent the subsurface flow paths in chalk catchments While it was able to represent catchment-scale response, the simulations could not be reconciled with site-specific data on loadings and observed borehole water quality data More complex groundwater systems may have flow paths associated with de-nitrification (Lovett et al., 2006) A much improved understanding is needed of groundwater flow dynamics and geochemistry for reductions to be made with reasonable confidence Urban flooding Integrated decision support tools The effects of urbanisation are well understood The basic problem is that the runoff response is strongly influenced by local management interventions The multi-scale problem recurs of how to represent local detail in catchment scale impact assessment Methods developed for rural land use could in principle be applied to this problem However, the authors are not aware of any significant research to address this issue In the context of flooding, DEFRA’s policy document Making Space for Water (2004) defines the need for a holistic approach to land and water management DEFRA-funded research (Wheater et al., 2007) has set out a medium term vision to achieve this It emphasises both integrated modelling systems that can represent effects on flow, sediments and habitats, and the interface H Wheater, E Evans / Land Use Policy 26S (2009) S251–S264 with socio-economic effects on both drivers and receptors of risk Effective land management clearly needs integrated models for catchment planning and management They must cover surface water and groundwater systems, flow, water quality, sediments, habitats, and socio-economic interactions, and have national applicability Implementation could be possible in 5–10 years, but only with a major investment in resources Climate change Finally we turn to climate change, and the improved science needed to support assessment of climate change impacts on land use and water These include: • improved understanding of the climate system, recognising that factors such as future precipitation are poorly understood, particularly with respect to extremes, persistence, and the effects of weather patterns, and that improved downscaling methods are needed, • improved understanding of climate change impacts on soil structure, biogeochemical cycles and hydrological processes This work is in its infancy, with a 10 year horizon for significant progress, • improved understanding of climate change effects on ecosystems, and the development of policy for habitat protection under a changing climate Little work has been done in this area, and there is a 10-year horizon for major progress Conclusion In conclusion we cannot better than quote from the Executive Summary of the 2004 Foresight Future Flooding study (OST, 2004) the factors which should inform our long-term approach to flood management, all of which have important implications for the future of 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England Chalk groundwater is recharged by water travelling through an unsaturated zone that can be up to 100 m deep Recent research has addressed uncertainties in H Wheater, E Evans / Land Use Policy