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Comparing local and global water scarcity information in determining the water scarcity footprint of potato cultivation in Great Britain
Journal of Cleaner Production 87 (2015) 666e674
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Comparing local and global water scarcity information in determining the water scarcity footprint of potato cultivation in Great Britain T.M. Hess a, *, A.T. Lennard a, b, A. Daccache a a b
Cranfield Water Science Institute, Cranfield University, Bedfordshire MK43 0AL, UK School of Environmental Sciences, University of Liverpool, Liverpool L69 7ZT, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 May 2014 Received in revised form 29 September 2014 Accepted 24 October 2014 Available online 31 October 2014
In Great Britain (GB), more water is abstracted from surface and groundwater resources for the irrigation of potatoes than for any other crop. This abstraction occurs in the driest catchments and at the driest times of year, and therefore has the potential to exacerbate pressures on water supplies and aquatic ecology. The water scarcity footprint is a metric that describes the impact of an activity on the water scarcity in a locality. In this paper, we use the concept to estimate the volume of blue water consumed in potato production in an average year for the potato growing regions of GB. This has been contextualised by weighting the water consumption according to a global map of water scarcity (Ridoutt and Pfister, 2010) and a local assessment of water resource availability (Environment Agency, 2002). Average blue water consumption for the cultivation of potatoes in Great Britain is 61 Mm3 per year, equivalent to 11 m3/t. The global map of water scarcity was shown to be insufficient for identifying “hotspots”, however the combination of water consumption estimates and local water resource availability assessments allowed the identification of catchments where potato production may be contributing to water scarcity. The East of England was identified as a “hotspot” of water related risk for potato production due to the large area of production, high irrigation need and the fact that many of the catchments are already over abstracted or over licenced. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Blue water Impact assessment Potato Water footprint Water risk Water scarcity
1. Introduction Global supplies of freshwater are increasingly under pressure. Population growth, continuing industrialisation and the need for increased agricultural production all exacerbate stresses on this vital resource. The World Economic Forum identified water crises, resulting from mismanagement and increased competition, as the third highest risk of global concern (WEF, 2014). Given that agriculture accounts for >70% of global freshwater withdrawals, (Comprehensive Assessment of Water Management in Agriculture (2007)) the sustainable use of freshwater for food production is an increasing concern for governments, businesses and society. Water use for agriculture has the potential to cause environmental harm through the exploitation and potential pollution of water resources (Hess et al., 2014) whilst the security of water resources creates a risk for food supply chains (Kelly, 2014). It is therefore critical to examine water use, water availability and associated
* Corresponding author. Tel.: þ44 1234 750111. E-mail address: t.hess@cranfield.ac.uk (T.M. Hess). http://dx.doi.org/10.1016/j.jclepro.2014.10.075 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
environmental impacts of agriculture to aid understanding for current and future resource management and to assess water related risk in food supply chains. The term ‘water footprint’ was introduced by Hoekstra and Hung (2002) as an analogy to the ‘ecological footprint’ developed by Wackernagel and Rees (1996) and built on the concept of virtual water proposed by Allan (1998). It was defined as the life-cycle water consumption of a commodity or product, and was an indicator of the human appropriation of water associated with production. The concept has been applied to a range of commodities and products - for example, cotton (Chapagain et al., 2006); tea and coffee (Chapagain and Hoekstra, 2007); bio-energy (GerbensLeenes et al., 2009); food-waste (Ridoutt et al. 2010); and wheat (Mekonnen and Hoekstra, 2010). Whilst this provides an indication of the human appropriation of the global water resources, it reveals little on the impact on the environment or other water users, or the risk to agriculture associated with water availability. During the early phases of water footprinting, impact assessments were largely disregarded (Hoekstra et al., 2011) and water footprints based on total volume of water consumed have been criticised for being ‘misleading and confusing’ (Ridoutt and Pfister, 2010:117), lacking environmental relevance (Ridoutt and Huang, 2012) and
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disregarding the impacts of water resources on livelihoods, other natural resources, or environmental amenities (Wilchens, 2011). It is common to differentiate between water that is withdrawn from surface or groundwater resources (blue water) and rainfall that is used at the point where it falls (green water) (Falkenmark, 1995). This differentiation is important as, generally, green water has little, or no, alternative use except for environmental uses, whereas blue water use is in competition with other industrial, domestic and environmental uses. However, the blue water consumed in the production of a commodity may have come from different sources (rivers, groundwater and reservoirs); in different locations (regions, countries); and been withdrawn at different times (seasons). A total blue water consumption estimate would not distinguish between these different withdrawals and Pfister and Hellweg (2009) perceived the blue water footprint as simply a water “shoesize”. In order to evaluate the impact of production on water scarcity, the blue water consumption must be put into the context of the water resources at the place of withdrawal. For example, 100 m3 of water taken from a water-stressed catchment is likely to have a higher impact on other water uses than an equivalent volume taken from a catchment where water is abundant. Reducing blue water consumption in areas of water scarcity will release water for other uses and understanding the volumes and sources of water consumed in the production of goods in relation to local water scarcity can help businesses mitigate the risks presented by water scarcity (Hoekstra, 2014). Qualitative and quantitative water footprint impact assessment methods have been developed using various water stress or water scarcity indices to identify the vulnerability of the water sources where withdrawal is located. In a study of the water footprint of the Netherlands, van Oel et al. (2008) identified ‘hotspots’ where the volumetric water footprints were large and water scarcity was high. This comparison showed that the biggest impact of Dutch consumption was not necessarily in those countries where the water footprint was largest. Pfister and Hellweg (2009) suggested that weighting is required to express volumes of water consumed in terms of potential impact on water scarcity and several studies have developed impactorientated water footprints as part of Life Cycle Analysis (LCA) studies (Berger and Finkbeiner, 2010). Many indicators have been used to characterise volumetric water footprints based on human water requirements, water resources or environmental requirements (see Kounina et al., 2013; Brown and Matlock, 2011; White, 2012; UNEP, 2012; for reviews) and Jeswani and Azapagic (2011) showed how using different methods results in a huge i Canals variation in the interpretation of water footprints. Mila et al. (2009) developed Life Cycle Impact Assessment (LCIA) characterisation factors based on the environmental water stress indicator (EWSI) (Smakhtin et al., 2004) to estimate how consumptive water use can impact water availability and affect ecosystems. The freshwater ecosystem impact (FEI) is a measure of ‘ecosystemequivalent’ water and is expressed in ecosystem equivalent volumes (Mil a i Canals et al., 2009). The withdrawal-to-availability (WTA) ratio (Alcamo et al., 2003a) is a representative proxy for water scarcity (Kounina et al., 2013) and many studies (e.g. Ercin et al., 2011; Jefferies et al., 2012; Gerbens-Leenes and Hoekstra, 2012) have used global maps of WTA to compare alternative locations. Ridoutt and Pfister (2010) developed a Water Stress Index (WSI) calculated using the WTA ratio from the Water GAP 2 model (Alcamo et al., 2003b). The WSI was calculated from the WTA ratio corrected by a variation factor that considers the variability of annual and monthly precipitation and how strongly flows are regulated in the basin (Pfister et al., 2009). The volume of blue
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water consumed was weighted by the WSI value of the basin where the consumption was located to produce an impact-orientated water footprint. The weighted consumption can also be normalised by the global average WSI (e.g. Ridoutt et al., 2010; De Boer et al., 2013) or the average WSI for the country of production (Page et al., 2012) to express the consumption as an H2O equivalent (H2Oeq) of freshwater water use at a global or national level respectively. A water footprint that considers only the impact of water consumption on water scarcity is known as a “water scarcity footprint” (ISO, 2014). Although agriculture accounts for <2% of total freshwater withdrawals in Great Britain (GB, i.e., England, Wales & Scotland), irrigation potentially has a large impact on water resources. By definition, its use is restricted to a few months and the driest years when resources are most constrained; it is concentrated in the driest areas of the country; and it is a consumptive use e that is, water is not returned to the environment in the short term. As a result, irrigation can be the largest abstractor in some catchments in some dry summers. More water is used for the irrigation of potatoes than any other crop in GB and potatoes account for 43% of the total irrigated area and 54% of irrigation water use in England and Wales1 (Defra, 2011). Potato production has the potential to contribute to local water scarcity more than any other crop. Nationally, 127,000 ha are planted with potatoes across mainland GB, with an average (2004e2013) annual production of 5.7 Mt and a yield of 44.6 t/ha (Potato Council, 2014). Although potatoes can be grown without irrigation in many regions of GB, supplementary irrigation is often used to ensure crop yield and particularly quality. As yield is a function of many agronomic factors including planting date, variety, soil type and location and there is no significant difference in the average yield between irrigated and non-irrigated potatoes in GB. This paper aims to estimate the potential impact of potato production on water scarcity in GB and to identify the regions where water related risks are greatest. It will determine the total water consumption of ware potato cultivation in GB and compare impact assessment based on global water scarcity maps with local water resource assessment in order to test whether global water scarcity maps can adequately capture local water resource vulnerability. 2. Material and methods 2.1. Water consumption Although potatoes are grown in all regions of GB, cultivation is concentrated in particular areas where soil and climate conditions are favourable (Daccache et al., 2012). Thirteen locations were identified in the areas where potato cultivation is concentrated (Fig. 1) and crop evapotranspiration for potatoes was estimated using the CROPWAT 8.0 software (FAO, 2009) and average (1981e2010) monthly climate data (Met Office, 2012) (Table 1). Average annual blue (BWC) and green (GWC) water consumption from evapotranspiration (m3/t) were estimated for each location using the methods presented by Hoekstra et al. (2011) and recommended by Hess (2010) for temperate climates. Main crop potatoes in the UK are usually planted from mid-March to mid-May and are harvested from mid-August to mid-November; therefore a planting date of 1st April has been selected with a season length of 175 days. Crop development stages and crop parameters were estimated from FAO (2012). The dominant soil types across all the growing sites are either loamy, sandy loams or sandy soils,
1
Comparable figures are not available for Scotland.
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Fig. 1. a) Potato growing areas (green) and location of representative weather stations (C) and b) regions in Great Britain. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
therefore a sandy loam with a maximum rooting depth of 0.7 m and an available water capacity of 150 mm/m was chosen as a representative soil type for all growing locations. A typical irrigation schedule was defined as an application of 25 mm when the soil moisture deficit reaches 25 mm which is typical for supplementary irrigation of main crop potatoes in the GB (MAFF, 1982). Typically, at harvest 80% of the mass of potatoes is water which equates to 0.8 m3/t of incorporated water to be added to the evapotranspiration in addition to the indirect, or virtual, water associated with inputs (such as agrochemicals, fertilizers and energy). Water consumption of inputs are generally insignificant compared to evapotranspiration and have been ignored. Therefore the BWC of potato production includes only consumed irrigation water. In order to extrapolate the BWC from the 13 locations to all growing locations, a regression was performed between the station BWC and the average (1961e1990) maximum potential soil
Table 1 Location of representative climate stations and long-term average annual reference evapotranspiration, ETo, rainfall and maximum potential soil water deficit, PSMDmax. Site Blackpool Boulmer Cambridge High Mowthorpe Leuchars Marham Ross-on-Wye Shawbury St Mawgan Tenby Waddington Wattisham Wye
Latitude N
Longitude E
Annual ETo, mm
Annual rain, mm
PSMDmax mm
53.77 55.41 52.19 54.10 56.40 52.65 51.91 52.79 50.43 51.67 53.18 52.12 51.19
3.04 1.60 0.13 0.64 2.86 0.57 2.58 2.66 4.99 4.71 0.52 0.96 0.94
648.3 593.1 729.4 610.0 632.6 698.1 714.0 684.7 639.6 628.6 672.7 713.9 645.6
818.3 689.3 568.1 751.4 690.9 652.6 733.7 659.9 1017.4 1110.9 614.4 613.8 741.1
76.1 54.8 217.0 90.6 105.4 164.9 154.4 132.9 86.1 51.9 167.2 202.4 161.8
moisture deficit (PSMDmax) which has been shown to be a useful agroclimatic indicator that is well correlated with irrigation need (Knox et al., 1997). The location and area of ware potato cultivation in GB in 2009 was determined from survey data of 106,000 ha (Potato Council, Pers. Com.) which also recorded whether or not the crop was irrigated. The regression was used to estimate the BWC for each irrigated location. For rain-fed locations, BWC was assumed to be zero. Average blue water consumption for each region (BWCr) was estimated from.
BWCr ¼
Pi¼n
i¼1 ðBWCi Areai Þ Pi¼n i¼1 Areai
(1)
where, BWCr is the blue water consumption in region r, m3/t BWCi is the estimated blue water consumption at location i, m3/t Areai is the area of cultivation at location i, ha 2.2. Contribution to water scarcity An impact-orientated quantitative assessment, based on global maps of water withdrawals and availability from the Water GAP 2 model (Alcamo et al., 2003b) was used to assess the water scarcity footprint following the approach outlined by Ridoutt and Pfister (2010). The Water Stress Index (WSI) is defined as a logistic function of the modified withdrawal-to-availability ratio (WTA*)
WSI ¼
1 *
1 þ e6:4WTA
1 0:01
(2)
1
A WSI < 0.1 represents “low”; 0.1 WSI < 0.5 “moderate” and WSI 0.5 “severe” water stress on a global scale (Pfister et al., 2009). A global map of WSI (www.ifu.ethz.ch) was used to derive WSI for each growing location.
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The average WSI for potato growing areas of each region of GB was calculated as the average of the WSI for each grower location (WSIi) in a region, weighted by the area of production (areai).
WSIr ¼
Pi¼1
WSIr is the average water stress index of the potato growing locations in region r. The potential contribution to water scarcity is the product of production, blue water consumption and WSI. BWC in each region (BWCr) was weighted by the WSIr and normalised by dividing by the national average WSI (Ridoutt et al., 2010; Page et al., 2012) to produce a water scarcity footprint (WSFr) expressed as an equivalent (m3 H2Oeq) of freshwater water use at a national level.
WSIr WSIaverage
Definition
Water is likely to be available at all flows including low flows. Restrictions may apply. No water available No water is available for further licensing at low flows. Water may be available at higher flows with appropriate restrictions. Over-licensed Current actual abstraction is such that no water is available at low flows. If existing licences were used to their full allocation they could cause unacceptable environmental damage at low flows. Water may be available at high flows, with appropriate restrictions. Over-abstracted Existing abstraction is causing unacceptable damage to the environment at low flows. Water may still be available at high flows, with appropriate restrictions. Water available
where
WSFr ¼ BWCr
Table 2 Definition of water resource availability in Catchment abstraction management strategies. Water resource availability status
i¼n WSIi areai Pi¼1 i¼n areai
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(3)
where WSFr is the contribution to water scarcity in region i, m3 H2Oeq WSIaverage is the national average WSI ¼ 0.082.
2.3. Hotspot identification Hotspot identification may be useful in a business context to identify areas for further investigation and prioritise response strategies (Jefferies et al., 2012) and provide useful information for focussing water risk mitigation strategies. Hotspots are locations where the blue water consumption is large and water scarcity is high (Hoekstra et al., 2011). In these locations, water related risks are highest. Hotspots were identified by comparing the BWCi to the water resource status at each location. In England and Wales, local assessments of water resource availability were carried out as part of the Catchment Abstraction Management Strategies (CAMS) (Environment Agency, 2010). Each major catchment has been divided into Water Resource Management Units (WRMUs) and the water availability status of surface and groundwater was determined, based on a water balance of each WRMU (Environment Agency, 2002). This included the quantification of river flows, groundwater recharge, abstractions and discharges back into water bodies and a hydro-ecological environmental weighting based on the ecological sensitivity of rivers to abstraction. Water resource availability was categorised according to ability of the water body to support further water withdrawals (Table 2). The hotspot analysis has been applied to England and Wales only as Scotland was not covered by CAMS. However, all water bodies in GB have been assessed for ecological status and pressures for the Water Framework Directive. Water bodies where pressure from abstraction has been identified can be compared across GB. Grower locations in catchments of water bodies at risk of failure to meet good ecological status in part due to pressures from abstraction (Scotland) or “at risk” or “probably at risk” (England and Wales) have been identified. This allows water risk in Scottish potato growing locations to be compared with hotspots in England and Wales.
evapotranspiration of the production area and is largest at Cambridge (86 m3/t) and smallest at Boulmer (67 m3/t). Whilst there is little variation in the volume of green water consumed per ton of production (62.6 ± 1.6 m3/t), the potential blue water consumption exhibits a wide variation. In an average year, the blue water consumption of a fully irrigated crop accounts for a quarter to a fifth of the total water consumption at Cambridge (29%), Wattisham (27%), Ross-on-Wye (26%), Marham (23%), Wye (22%), Shawbury (22%) and Waddington (19%). At these sites, it is likely that, if available, irrigation would be used in most years in order to ensure quality of production and yield. Blue water accounts for a smaller proportion of the total at Leuchars (15%), High Mowthorpe (13%) and Boulmer (10%). At Blackpool (9%), St Mawgan (7%) and Tenby (3%) it may not be economic to invest in irrigation and irrigation may only be used on some farms in dry summers if equipment is available. In South West and North West less than 25% of the potato growing area was recorded as being irrigated (Table 3). The relationship between BWC and PSMDmax was described by;
BWC ¼ 0:15PSMDmax 3:69 R2 ¼ 0:91; p < 0:001
(5)
Taking into account the proportion of the crop that is actually irrigated, the average blue water consumption for potatoes in GB is 11 m3/t, but there is a large range from 19 m3/t for potatoes grown in the East of England to 2 m3/t for potatoes grown in the North West (Fig. 3). Given a total production of 5.68 Mt, an estimated 61 Mm3 of water is consumed (as opposed to withdrawn) from freshwater resources for irrigation of potatoes in GB in an average year.
3. Results 3.1. Water consumption The BWC and GWC for each site are presented in Fig. 2. The total water consumption depends largely on the potential
Fig. 2. Estimated blue and green water consumption, m3/t, of an irrigated potato crop at thirteen locations in Great Britain.
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Table 3 Annual potato production, % irrigated and water stress index (WSI) for regions of Great Britain. Region
Production, Mt
% Irrigated
BWC, Mm3
WSIa
East of England South East East Midlands West Midlands Yorkshire and the Humber North East Wales Scotland South West North West Total
1.65 0.16 0.81 0.77 0.73 0.06 0.08 0.83 0.33 0.27 5.68
80% 68% 51% 53% 47% 65% 65% 61% 17% 22% 58%
32.2 2.7 8.5 7.1 5.4 0.3 0.4 3.5 0.9 0.5 61.4
0.164 0.366 0.139 0.098 0.140 0.120 0.088 0.017 0.040 0.667 0.148
a Average WSI for potato growing locations within the region, weighted by area of production.
3.2. Contribution to water scarcity The average WSI for potato growing locations in GB is 0.148, compared to an average for all GB of 0.082 (Table 3), suggesting that potatoes tend to be grown in areas that are more water-stressed than the average for the country. Therefore, water used for irrigating potatoes has a disproportional impact on national water scarcity. WSIr ranges from 0.017 in Scottish potato growing areas to 0.667 for potato growing areas in the North West. On this basis, 1 m3 of water abstracted in the North West, for example, has about 40 times the impact on water scarcity of an equivalent volume abstracted in Scotland. The WSFr, expressed per ton potatoes, is 21 m3 H2Oeq and ranges from 83 m3 H2Oeq t1 in the South East e where the need for irrigation is higher and there is moderate water stress (WSIr ¼ 0.366) e to <1 m3 H2Oeq t1 in Scotland (Fig. 3). Although the WSI shows potato growing regions in the North West to have “severe water stress” (WSIr ¼ 0.667) the region has the lowest irrigation requirement, such that the water scarcity footprint per ton of potatoes (17 m3 H2Oeq) is lower than that of the South East, East Midlands and East of England. The national WSF of GB potato cultivation is equivalent to 115 Mm3 H2Oeq, i.e., equivalent to 115 Mm3 of water drawn equally from across GB. More than half of this (65 Mm3 H2Oeq) is due to
Table 4 Average water stress index and proportion of area of production in catchments classified according to water resource status in England & Wales. WSIr
Over Over No water Water abstracted licensed available available
East of England 0.164 34% South East 0.366 50% East Midlands 0.139 36% West Midlands 0.098 23% Yorkshire and the Humber 0.140 10% North East 0.120 0% Wales 0.088 0% South West 0.040 14% North West 0.667 1% Total 0.667 25%
23% 18% 8% 9% 26% 3% 21% 6% 21% 17%
35% 27% 44% 62% 59% 0% 66% 24% 46% 45%
8% 6% 12% 6% 5% 97% 13% 56% 33% 13%
potato production in the East of England, where a large area of production (z30% of national production) coincides with a high irrigation need and “moderate” water scarcity (WSIr ¼ 0.164). Although a significant proportion of national production is from Scotland (z15%) the low level of water scarcity (WSIr ¼ 0.017) and lower irrigation need means that it only contributes less than 1% of the total WSF (Fig. 3). 3.3. Hotspot identification When comparing the location of potato production with the resource availability status, 17% and 25% of the potato production areas (Table 4) are in WRMUs defined as over abstracted (i.e., where abstraction is causing unacceptable damage to the environment at low flows) or over licenced (i.e., where unacceptable damage could be caused if all abstractors used their full licensed amount) respectively. These account for 35% and 19% of the blue water consumption in potato production (Table 5) respectively. The East of England is clearly identified as a hotspot with the largest contribution to national BWC and 62% of the water consumed coming from WRMUs that are either over abstracted or over licenced. Potato production in the East of England is therefore potentially vulnerable to drought and the potential for increased abstraction (for expansion of production or to mitigate the impacts of climate change) are limited.
Fig. 3. Average blue water consumption, m3/t, (solid) and water scarcity footprint (hatched) for potato production in Great Britain.
T.M. Hess et al. / Journal of Cleaner Production 87 (2015) 666e674 Table 5 Blue water consumption, Mm3, for potato production and proportion of blue water consumption from catchments classified according to water resource status in England & Wales.
East of England South East East Midlands West Midlands Yorkshire and the Humber North East Wales South West North West Total
BWC Mm3
Over abstracted
Over licensed
No water available
Water available
29.5 2.5 7.8 6.5 5.0
39% 54% 35% 33% 15%
24% 15% 7% 11% 22%
33% 23% 48% 51% 61%
5% 9% 10% 5% 2%
0.3 0.4 0.8 0.5 56.4
0% 0% 7% 0% 35%
3% 35% 17% 30% 19%
0% 45% 30% 58% 40%
97% 20% 45% 13% 7%
Fig. 4 shows the area of potato production in catchments of water bodies at risk of failure to meet Good Ecological Status due to abstraction pressure for regions of GB. It shows that a larger area of Scottish production is in catchments of higher water risk than any region in England. However, because the BWC per ton in Scotland is lower (i.e., most of the water requirements of the potatoes in Scotland are met by rainfall) the volume of water consumed from high risk catchments is considerably lower than the East of England, but comparable to the Yorkshire and the Humber region in England. 4. Discussion The need for water for irrigation for potato cultivation varies across GB reflecting the range of climatic conditions under which potatoes are grown, and even in the East of England, the driest part of the country, 20% of the cropped area is reported as not irrigated. Water resource availability also varies significantly and as a result the potential impact of potato production on water scarcity, and the water related supply-chain risk, varies considerably across the country. Although the East of England accounts for about a third of the national area of potato cultivation, it accounts for more than half of the national blue water consumption for potato cultivation, whereas Scotland accounts for 15% of the area but only 6% of the total blue water consumption (Fig. 5). When weighted for water
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scarcity, the East of England is responsible for 56% of the potential national impact compared to <1% in Scotland. Although the South East of England accounts for only 3% of the area of cultivation, it has a disproportionate share of the national impact due to higher water scarcity in the region. The WSIr does not always identify the same hotspots as the CAMS water resource availability status. The potato growing areas of the South East have the highest WSIr (0.366) and the highest proportion of production in catchments that are over abstracted or over licensed. In the North East (WSIr ¼ 0.120) none of the production is from catchments that are over abstracted and only 3% from over licenced catchments in contrast to Yorkshire and the Humber, with a similar WSIr (0.140), where 36% of the production area is in over abstracted or over licenced catchments. This suggests the global-scale map of Pfister et al. (2009) may not adequately reflect the local nature of water scarcity. A number of issues have been associated with the WSI is based on the Water GAP 2 global hydrological model: 1. Scale: The Water GAP 2 model was not intended for application at small scales, and aimed to provide a global overview rather than specific details about water resource impacts (Alcamo et al., 2003b). Similarly, annual average water balances conceal significant seasonal variations. 2. Validation: The Water GAP 2 model was tested using data from 724 river gauging stations globally (Alcamo et al., 2003b) and had at least a satisfactory fit for most of Europe, however only a very limited area of south east England was included in the validation dataset. Therefore, there could be considerable uncertainty in the modelled WTA ratios for the rest of GB. 3. Withdrawal and consumption: WTA ratios may not be the appropriate indicators when assessing impact as they do not take account of environmental flows (Hoekstra and Mekonnen, 2011). 4. In industrialised countries large proportions of withdrawals are used but not consumed, returning water to the supplying water body. This may account for the apparent severe water stress in the North West, which has the same, or more extreme, values of WSI as Southern Spain and North Africa whereas the local resource assessment shows few over abstracted catchments. For this reason a consumption-to-availability ratio may be a more meaningful indicator of water scarcity (Boulay et al., 2011).
Fig. 4. Potato area (000 ha) and BWC (Mm3) for potatoes from catchments of water bodies at risk of failure to meet Good Ecological Status due to abstraction pressure in GB.
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Fig. 5. Relative area of production of potatoes, blue water consumption and contribution to water scarcity for regions of Great Britain.
5. Indices derived at the basin scale fail to differentiate between upstream and downstream water use (Jeswani and Azapagic, 2011). Water consumption may have a lower impact on water scarcity where there are fewer downstream uses. The hotspot approach suffers from its qualitative nature. There is no definition of what is a large volumetric water footprint. Such value judgements are open to interpretation which could lead to varying and inconsistent impact assessments. However, as shown in this case study, it allows the identification of places where there is potential for environmental damage resulting from water consumption which may be useful to direct further, more detailed studies. Although this study has followed commonly used methodologies used to estimate the potential contribution of agriculture to water scarcity (e.g. Chapagain and Hoekstra, 2007; Ridoutt et al., 2010; Jefferies et al., 2012) it suffers from a number of limitations: 1. The assessments only indicate the ‘potential’ contribution to water scarcity and local practice and regulation may mitigate such damage. For example, many potato growers in water stressed areas abstract during the winter and store the water in on-farm reservoirs for summer use to supplement summer
abstraction, accounting for about 20% of annual abstraction (Weatherhead, pers. com.). 2. The assessment is based on average climate data. The biggest impact on water scarcity and risk to production will not be in average years, but in dry years when both demand for irrigation water is higher and water resource availability is lower. 3. The focus on water consumption recognises that a proportion of the irrigation water withdrawn is returned to the environment, and only the proportion lost to evapotranspiration is assumed to have been lost. However, return of drainage water may not occur until the winter following abstraction. The impact on water scarcity in the short-term is therefore related to abstraction rather than consumption.
5. Conclusion This study has estimated the average annual blue water consumption for the cultivation of potatoes in GB at 61 Mm3, equivalent to 11 m3/t. However, as potatoes tend to be grown in the parts of the country where water resources are under more stress, water used for irrigating potatoes has the potential to generate a disproportionate impact on local water scarcity. If the WSI is used
T.M. Hess et al. / Journal of Cleaner Production 87 (2015) 666e674
to weight the water consumption according to water stress, this volume of water is equivalent to 115 Mm3 of water drawn equally from across the country. The East of England is a particular hotspot for potato production accounting for more than half of the potential impact on water scarcity and more than half of the potato production in this region is from catchments classified as over abstracted or over licenced. As identified by Kounina et al. (2013), there is, as yet, no preferred method for characterising the impacts of water withdrawal or consumption. Whilst the global-scale map of Pfister et al. (2009) has identified regions of potato production in GB where water withdrawal may be have a greater of lesser impact, the casestudy has shown how local information on water resource availability can provide a deeper and richer understanding of catchment specific vulnerability than may be derived from the global perspective an LCA database. Similarly, national or basin level assessments of water scarcity may be not appropriate for assessing the actual impacts of water use as there may be considerable local differences within a nation or basin. This emphasises the highly localised nature of water scarcity and the need to select an impact assessment method that is most relevant to the objectives of the study (Kounina et al., 2013). In the future, there is likely to be greater need to quantify the impact of a supply chain on the water environment in order to understand water-related risk and to support product assurance schemes or certification (Postle et al., 2011). Whilst estimates of water scarcity may identify where there is potential for water use to be having a greater impact, it fails to identify actual impact. For example, the potential impact of water withdrawal, and associated supply chain risk, may be mitigated by careful management onfarm water management (Hess et al., 2010) and especially the use of on-farm storage to allow abstraction at times of high flow (Weatherhead et al., 2010). This broad-scale assessment, however, provides a basis for targeting local data collection and support to growers to adapt to climate change and mitigate water related risks. Acknowledgements The authors would like to thank Potato Council (a division of the Agriculture & Horticulture Development Board) for the provision of statistical data on potato production in Great Britain. References €ll, P., Henrichs, T., Kaspar, F., Lehner, B., Ro €sch, T., Siebert, S., 2003a. Alcamo, J., Do Global estimates of water withdrawals and availability under current and future “business-as-usual” conditions. Hydrol. Sci. J. 48 (3), 339e348. €ll, P., Henrichs, T., Kaspar, F., Lehner, B., Ro €sch, T., Siebert, S., 2003b. Alcamo, J., Do Development and testing of the WaterGAP 2 global model of water use and availability. Hydrol. Sci. J. 48 (3), 317e337. Allan, J.A., 1998. Virtual water: a strategic resource. Global solutions to regional deficits. Groundwater 36 (4), 545e546. Berger, M., Finkbeiner, M., 2010. Water footprinting: how to address water use in life cycle assessment? Sustainability 2 (4), 919e944. ^nes, L., Margni, M., 2011. Regional Boulay, A.-M., Bulle, C., Bayart, J.-B., Desche characterization of freshwater use in LCA: modeling direct impacts on human health. Environ. Sci. Technol. 45, 8948e8957. Brown, A., Matlock, M., 2011. A Review of Water Scarcity Indices and Methodologies. Water Paper no. 106. The Sustainability Consortium, The University of Arkansas. Chapagain, A.K., Hoekstra, A.Y., 2007. The water footprint of coffee and tea consumption in the Netherlands. Ecol. Econ. 64 (1), 109e118. Chapagain, A.K., Hoekstra, A.Y., Savenije, H.H.G., Gautam, R., 2006. The water footprint of cotton consumption: an assessment of the impact of worldwide consumption of cotton products on the water resources in the cotton producing countries. Ecol. Econ. 60, 186e203. Comprehensive Assessment of Water Management in Agriculture, 2007. Water for Food, Water for Life: a Comprehensive Assessment of Water Management in Agriculture. Earthscan, and Colombo: International Water Management Institute, London.
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Irrigation. Reference Book 138, fifth ed. Her Majesty's Stationery Office, London. Mekonnen, M.M., Hoekstra, A.Y., 2010. A global and high-resolution assessment of the green, blue and grey water footprint of wheat. Hydrol. Earth Syst. Sci. 14 (7), 1259e1276. Met Office, 2012. 1981e2010 Climate Averages accessed on 13/05/2013 at. http:// www.metoffice.gov.uk/climate/uk/averages/19812010/. i Canals, L., Chenoweth, J., Chapagain, A., Orr, S., Antόn, A., Clift, R., 2009. Mila Assessing freshwater use impacts in LCA: Part I e inventory modelling and characterisation factors for the main pathways. Int. J. Life Cycle Assess. 14 (1), 28e42.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Comparing local and global water scarcity information in determining the water scarcity footprint of potato cultivation in Great Britain T.M. Hess a, *, A.T. Lennard a, b, A. Daccache a a b
Cranfield Water Science Institute, Cranfield University, Bedfordshire MK43 0AL, UK School of Environmental Sciences, University of Liverpool, Liverpool L69 7ZT, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 May 2014 Received in revised form 29 September 2014 Accepted 24 October 2014 Available online 31 October 2014
In Great Britain (GB), more water is abstracted from surface and groundwater resources for the irrigation of potatoes than for any other crop. This abstraction occurs in the driest catchments and at the driest times of year, and therefore has the potential to exacerbate pressures on water supplies and aquatic ecology. The water scarcity footprint is a metric that describes the impact of an activity on the water scarcity in a locality. In this paper, we use the concept to estimate the volume of blue water consumed in potato production in an average year for the potato growing regions of GB. This has been contextualised by weighting the water consumption according to a global map of water scarcity (Ridoutt and Pfister, 2010) and a local assessment of water resource availability (Environment Agency, 2002). Average blue water consumption for the cultivation of potatoes in Great Britain is 61 Mm3 per year, equivalent to 11 m3/t. The global map of water scarcity was shown to be insufficient for identifying “hotspots”, however the combination of water consumption estimates and local water resource availability assessments allowed the identification of catchments where potato production may be contributing to water scarcity. The East of England was identified as a “hotspot” of water related risk for potato production due to the large area of production, high irrigation need and the fact that many of the catchments are already over abstracted or over licenced. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Blue water Impact assessment Potato Water footprint Water risk Water scarcity
1. Introduction Global supplies of freshwater are increasingly under pressure. Population growth, continuing industrialisation and the need for increased agricultural production all exacerbate stresses on this vital resource. The World Economic Forum identified water crises, resulting from mismanagement and increased competition, as the third highest risk of global concern (WEF, 2014). Given that agriculture accounts for >70% of global freshwater withdrawals, (Comprehensive Assessment of Water Management in Agriculture (2007)) the sustainable use of freshwater for food production is an increasing concern for governments, businesses and society. Water use for agriculture has the potential to cause environmental harm through the exploitation and potential pollution of water resources (Hess et al., 2014) whilst the security of water resources creates a risk for food supply chains (Kelly, 2014). It is therefore critical to examine water use, water availability and associated
* Corresponding author. Tel.: þ44 1234 750111. E-mail address: t.hess@cranfield.ac.uk (T.M. Hess). http://dx.doi.org/10.1016/j.jclepro.2014.10.075 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
environmental impacts of agriculture to aid understanding for current and future resource management and to assess water related risk in food supply chains. The term ‘water footprint’ was introduced by Hoekstra and Hung (2002) as an analogy to the ‘ecological footprint’ developed by Wackernagel and Rees (1996) and built on the concept of virtual water proposed by Allan (1998). It was defined as the life-cycle water consumption of a commodity or product, and was an indicator of the human appropriation of water associated with production. The concept has been applied to a range of commodities and products - for example, cotton (Chapagain et al., 2006); tea and coffee (Chapagain and Hoekstra, 2007); bio-energy (GerbensLeenes et al., 2009); food-waste (Ridoutt et al. 2010); and wheat (Mekonnen and Hoekstra, 2010). Whilst this provides an indication of the human appropriation of the global water resources, it reveals little on the impact on the environment or other water users, or the risk to agriculture associated with water availability. During the early phases of water footprinting, impact assessments were largely disregarded (Hoekstra et al., 2011) and water footprints based on total volume of water consumed have been criticised for being ‘misleading and confusing’ (Ridoutt and Pfister, 2010:117), lacking environmental relevance (Ridoutt and Huang, 2012) and
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disregarding the impacts of water resources on livelihoods, other natural resources, or environmental amenities (Wilchens, 2011). It is common to differentiate between water that is withdrawn from surface or groundwater resources (blue water) and rainfall that is used at the point where it falls (green water) (Falkenmark, 1995). This differentiation is important as, generally, green water has little, or no, alternative use except for environmental uses, whereas blue water use is in competition with other industrial, domestic and environmental uses. However, the blue water consumed in the production of a commodity may have come from different sources (rivers, groundwater and reservoirs); in different locations (regions, countries); and been withdrawn at different times (seasons). A total blue water consumption estimate would not distinguish between these different withdrawals and Pfister and Hellweg (2009) perceived the blue water footprint as simply a water “shoesize”. In order to evaluate the impact of production on water scarcity, the blue water consumption must be put into the context of the water resources at the place of withdrawal. For example, 100 m3 of water taken from a water-stressed catchment is likely to have a higher impact on other water uses than an equivalent volume taken from a catchment where water is abundant. Reducing blue water consumption in areas of water scarcity will release water for other uses and understanding the volumes and sources of water consumed in the production of goods in relation to local water scarcity can help businesses mitigate the risks presented by water scarcity (Hoekstra, 2014). Qualitative and quantitative water footprint impact assessment methods have been developed using various water stress or water scarcity indices to identify the vulnerability of the water sources where withdrawal is located. In a study of the water footprint of the Netherlands, van Oel et al. (2008) identified ‘hotspots’ where the volumetric water footprints were large and water scarcity was high. This comparison showed that the biggest impact of Dutch consumption was not necessarily in those countries where the water footprint was largest. Pfister and Hellweg (2009) suggested that weighting is required to express volumes of water consumed in terms of potential impact on water scarcity and several studies have developed impactorientated water footprints as part of Life Cycle Analysis (LCA) studies (Berger and Finkbeiner, 2010). Many indicators have been used to characterise volumetric water footprints based on human water requirements, water resources or environmental requirements (see Kounina et al., 2013; Brown and Matlock, 2011; White, 2012; UNEP, 2012; for reviews) and Jeswani and Azapagic (2011) showed how using different methods results in a huge i Canals variation in the interpretation of water footprints. Mila et al. (2009) developed Life Cycle Impact Assessment (LCIA) characterisation factors based on the environmental water stress indicator (EWSI) (Smakhtin et al., 2004) to estimate how consumptive water use can impact water availability and affect ecosystems. The freshwater ecosystem impact (FEI) is a measure of ‘ecosystemequivalent’ water and is expressed in ecosystem equivalent volumes (Mil a i Canals et al., 2009). The withdrawal-to-availability (WTA) ratio (Alcamo et al., 2003a) is a representative proxy for water scarcity (Kounina et al., 2013) and many studies (e.g. Ercin et al., 2011; Jefferies et al., 2012; Gerbens-Leenes and Hoekstra, 2012) have used global maps of WTA to compare alternative locations. Ridoutt and Pfister (2010) developed a Water Stress Index (WSI) calculated using the WTA ratio from the Water GAP 2 model (Alcamo et al., 2003b). The WSI was calculated from the WTA ratio corrected by a variation factor that considers the variability of annual and monthly precipitation and how strongly flows are regulated in the basin (Pfister et al., 2009). The volume of blue
667
water consumed was weighted by the WSI value of the basin where the consumption was located to produce an impact-orientated water footprint. The weighted consumption can also be normalised by the global average WSI (e.g. Ridoutt et al., 2010; De Boer et al., 2013) or the average WSI for the country of production (Page et al., 2012) to express the consumption as an H2O equivalent (H2Oeq) of freshwater water use at a global or national level respectively. A water footprint that considers only the impact of water consumption on water scarcity is known as a “water scarcity footprint” (ISO, 2014). Although agriculture accounts for <2% of total freshwater withdrawals in Great Britain (GB, i.e., England, Wales & Scotland), irrigation potentially has a large impact on water resources. By definition, its use is restricted to a few months and the driest years when resources are most constrained; it is concentrated in the driest areas of the country; and it is a consumptive use e that is, water is not returned to the environment in the short term. As a result, irrigation can be the largest abstractor in some catchments in some dry summers. More water is used for the irrigation of potatoes than any other crop in GB and potatoes account for 43% of the total irrigated area and 54% of irrigation water use in England and Wales1 (Defra, 2011). Potato production has the potential to contribute to local water scarcity more than any other crop. Nationally, 127,000 ha are planted with potatoes across mainland GB, with an average (2004e2013) annual production of 5.7 Mt and a yield of 44.6 t/ha (Potato Council, 2014). Although potatoes can be grown without irrigation in many regions of GB, supplementary irrigation is often used to ensure crop yield and particularly quality. As yield is a function of many agronomic factors including planting date, variety, soil type and location and there is no significant difference in the average yield between irrigated and non-irrigated potatoes in GB. This paper aims to estimate the potential impact of potato production on water scarcity in GB and to identify the regions where water related risks are greatest. It will determine the total water consumption of ware potato cultivation in GB and compare impact assessment based on global water scarcity maps with local water resource assessment in order to test whether global water scarcity maps can adequately capture local water resource vulnerability. 2. Material and methods 2.1. Water consumption Although potatoes are grown in all regions of GB, cultivation is concentrated in particular areas where soil and climate conditions are favourable (Daccache et al., 2012). Thirteen locations were identified in the areas where potato cultivation is concentrated (Fig. 1) and crop evapotranspiration for potatoes was estimated using the CROPWAT 8.0 software (FAO, 2009) and average (1981e2010) monthly climate data (Met Office, 2012) (Table 1). Average annual blue (BWC) and green (GWC) water consumption from evapotranspiration (m3/t) were estimated for each location using the methods presented by Hoekstra et al. (2011) and recommended by Hess (2010) for temperate climates. Main crop potatoes in the UK are usually planted from mid-March to mid-May and are harvested from mid-August to mid-November; therefore a planting date of 1st April has been selected with a season length of 175 days. Crop development stages and crop parameters were estimated from FAO (2012). The dominant soil types across all the growing sites are either loamy, sandy loams or sandy soils,
1
Comparable figures are not available for Scotland.
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Fig. 1. a) Potato growing areas (green) and location of representative weather stations (C) and b) regions in Great Britain. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
therefore a sandy loam with a maximum rooting depth of 0.7 m and an available water capacity of 150 mm/m was chosen as a representative soil type for all growing locations. A typical irrigation schedule was defined as an application of 25 mm when the soil moisture deficit reaches 25 mm which is typical for supplementary irrigation of main crop potatoes in the GB (MAFF, 1982). Typically, at harvest 80% of the mass of potatoes is water which equates to 0.8 m3/t of incorporated water to be added to the evapotranspiration in addition to the indirect, or virtual, water associated with inputs (such as agrochemicals, fertilizers and energy). Water consumption of inputs are generally insignificant compared to evapotranspiration and have been ignored. Therefore the BWC of potato production includes only consumed irrigation water. In order to extrapolate the BWC from the 13 locations to all growing locations, a regression was performed between the station BWC and the average (1961e1990) maximum potential soil
Table 1 Location of representative climate stations and long-term average annual reference evapotranspiration, ETo, rainfall and maximum potential soil water deficit, PSMDmax. Site Blackpool Boulmer Cambridge High Mowthorpe Leuchars Marham Ross-on-Wye Shawbury St Mawgan Tenby Waddington Wattisham Wye
Latitude N
Longitude E
Annual ETo, mm
Annual rain, mm
PSMDmax mm
53.77 55.41 52.19 54.10 56.40 52.65 51.91 52.79 50.43 51.67 53.18 52.12 51.19
3.04 1.60 0.13 0.64 2.86 0.57 2.58 2.66 4.99 4.71 0.52 0.96 0.94
648.3 593.1 729.4 610.0 632.6 698.1 714.0 684.7 639.6 628.6 672.7 713.9 645.6
818.3 689.3 568.1 751.4 690.9 652.6 733.7 659.9 1017.4 1110.9 614.4 613.8 741.1
76.1 54.8 217.0 90.6 105.4 164.9 154.4 132.9 86.1 51.9 167.2 202.4 161.8
moisture deficit (PSMDmax) which has been shown to be a useful agroclimatic indicator that is well correlated with irrigation need (Knox et al., 1997). The location and area of ware potato cultivation in GB in 2009 was determined from survey data of 106,000 ha (Potato Council, Pers. Com.) which also recorded whether or not the crop was irrigated. The regression was used to estimate the BWC for each irrigated location. For rain-fed locations, BWC was assumed to be zero. Average blue water consumption for each region (BWCr) was estimated from.
BWCr ¼
Pi¼n
i¼1 ðBWCi Areai Þ Pi¼n i¼1 Areai
(1)
where, BWCr is the blue water consumption in region r, m3/t BWCi is the estimated blue water consumption at location i, m3/t Areai is the area of cultivation at location i, ha 2.2. Contribution to water scarcity An impact-orientated quantitative assessment, based on global maps of water withdrawals and availability from the Water GAP 2 model (Alcamo et al., 2003b) was used to assess the water scarcity footprint following the approach outlined by Ridoutt and Pfister (2010). The Water Stress Index (WSI) is defined as a logistic function of the modified withdrawal-to-availability ratio (WTA*)
WSI ¼
1 *
1 þ e6:4WTA
1 0:01
(2)
1
A WSI < 0.1 represents “low”; 0.1 WSI < 0.5 “moderate” and WSI 0.5 “severe” water stress on a global scale (Pfister et al., 2009). A global map of WSI (www.ifu.ethz.ch) was used to derive WSI for each growing location.
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The average WSI for potato growing areas of each region of GB was calculated as the average of the WSI for each grower location (WSIi) in a region, weighted by the area of production (areai).
WSIr ¼
Pi¼1
WSIr is the average water stress index of the potato growing locations in region r. The potential contribution to water scarcity is the product of production, blue water consumption and WSI. BWC in each region (BWCr) was weighted by the WSIr and normalised by dividing by the national average WSI (Ridoutt et al., 2010; Page et al., 2012) to produce a water scarcity footprint (WSFr) expressed as an equivalent (m3 H2Oeq) of freshwater water use at a national level.
WSIr WSIaverage
Definition
Water is likely to be available at all flows including low flows. Restrictions may apply. No water available No water is available for further licensing at low flows. Water may be available at higher flows with appropriate restrictions. Over-licensed Current actual abstraction is such that no water is available at low flows. If existing licences were used to their full allocation they could cause unacceptable environmental damage at low flows. Water may be available at high flows, with appropriate restrictions. Over-abstracted Existing abstraction is causing unacceptable damage to the environment at low flows. Water may still be available at high flows, with appropriate restrictions. Water available
where
WSFr ¼ BWCr
Table 2 Definition of water resource availability in Catchment abstraction management strategies. Water resource availability status
i¼n WSIi areai Pi¼1 i¼n areai
669
(3)
where WSFr is the contribution to water scarcity in region i, m3 H2Oeq WSIaverage is the national average WSI ¼ 0.082.
2.3. Hotspot identification Hotspot identification may be useful in a business context to identify areas for further investigation and prioritise response strategies (Jefferies et al., 2012) and provide useful information for focussing water risk mitigation strategies. Hotspots are locations where the blue water consumption is large and water scarcity is high (Hoekstra et al., 2011). In these locations, water related risks are highest. Hotspots were identified by comparing the BWCi to the water resource status at each location. In England and Wales, local assessments of water resource availability were carried out as part of the Catchment Abstraction Management Strategies (CAMS) (Environment Agency, 2010). Each major catchment has been divided into Water Resource Management Units (WRMUs) and the water availability status of surface and groundwater was determined, based on a water balance of each WRMU (Environment Agency, 2002). This included the quantification of river flows, groundwater recharge, abstractions and discharges back into water bodies and a hydro-ecological environmental weighting based on the ecological sensitivity of rivers to abstraction. Water resource availability was categorised according to ability of the water body to support further water withdrawals (Table 2). The hotspot analysis has been applied to England and Wales only as Scotland was not covered by CAMS. However, all water bodies in GB have been assessed for ecological status and pressures for the Water Framework Directive. Water bodies where pressure from abstraction has been identified can be compared across GB. Grower locations in catchments of water bodies at risk of failure to meet good ecological status in part due to pressures from abstraction (Scotland) or “at risk” or “probably at risk” (England and Wales) have been identified. This allows water risk in Scottish potato growing locations to be compared with hotspots in England and Wales.
evapotranspiration of the production area and is largest at Cambridge (86 m3/t) and smallest at Boulmer (67 m3/t). Whilst there is little variation in the volume of green water consumed per ton of production (62.6 ± 1.6 m3/t), the potential blue water consumption exhibits a wide variation. In an average year, the blue water consumption of a fully irrigated crop accounts for a quarter to a fifth of the total water consumption at Cambridge (29%), Wattisham (27%), Ross-on-Wye (26%), Marham (23%), Wye (22%), Shawbury (22%) and Waddington (19%). At these sites, it is likely that, if available, irrigation would be used in most years in order to ensure quality of production and yield. Blue water accounts for a smaller proportion of the total at Leuchars (15%), High Mowthorpe (13%) and Boulmer (10%). At Blackpool (9%), St Mawgan (7%) and Tenby (3%) it may not be economic to invest in irrigation and irrigation may only be used on some farms in dry summers if equipment is available. In South West and North West less than 25% of the potato growing area was recorded as being irrigated (Table 3). The relationship between BWC and PSMDmax was described by;
BWC ¼ 0:15PSMDmax 3:69 R2 ¼ 0:91; p < 0:001
(5)
Taking into account the proportion of the crop that is actually irrigated, the average blue water consumption for potatoes in GB is 11 m3/t, but there is a large range from 19 m3/t for potatoes grown in the East of England to 2 m3/t for potatoes grown in the North West (Fig. 3). Given a total production of 5.68 Mt, an estimated 61 Mm3 of water is consumed (as opposed to withdrawn) from freshwater resources for irrigation of potatoes in GB in an average year.
3. Results 3.1. Water consumption The BWC and GWC for each site are presented in Fig. 2. The total water consumption depends largely on the potential
Fig. 2. Estimated blue and green water consumption, m3/t, of an irrigated potato crop at thirteen locations in Great Britain.
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Table 3 Annual potato production, % irrigated and water stress index (WSI) for regions of Great Britain. Region
Production, Mt
% Irrigated
BWC, Mm3
WSIa
East of England South East East Midlands West Midlands Yorkshire and the Humber North East Wales Scotland South West North West Total
1.65 0.16 0.81 0.77 0.73 0.06 0.08 0.83 0.33 0.27 5.68
80% 68% 51% 53% 47% 65% 65% 61% 17% 22% 58%
32.2 2.7 8.5 7.1 5.4 0.3 0.4 3.5 0.9 0.5 61.4
0.164 0.366 0.139 0.098 0.140 0.120 0.088 0.017 0.040 0.667 0.148
a Average WSI for potato growing locations within the region, weighted by area of production.
3.2. Contribution to water scarcity The average WSI for potato growing locations in GB is 0.148, compared to an average for all GB of 0.082 (Table 3), suggesting that potatoes tend to be grown in areas that are more water-stressed than the average for the country. Therefore, water used for irrigating potatoes has a disproportional impact on national water scarcity. WSIr ranges from 0.017 in Scottish potato growing areas to 0.667 for potato growing areas in the North West. On this basis, 1 m3 of water abstracted in the North West, for example, has about 40 times the impact on water scarcity of an equivalent volume abstracted in Scotland. The WSFr, expressed per ton potatoes, is 21 m3 H2Oeq and ranges from 83 m3 H2Oeq t1 in the South East e where the need for irrigation is higher and there is moderate water stress (WSIr ¼ 0.366) e to <1 m3 H2Oeq t1 in Scotland (Fig. 3). Although the WSI shows potato growing regions in the North West to have “severe water stress” (WSIr ¼ 0.667) the region has the lowest irrigation requirement, such that the water scarcity footprint per ton of potatoes (17 m3 H2Oeq) is lower than that of the South East, East Midlands and East of England. The national WSF of GB potato cultivation is equivalent to 115 Mm3 H2Oeq, i.e., equivalent to 115 Mm3 of water drawn equally from across GB. More than half of this (65 Mm3 H2Oeq) is due to
Table 4 Average water stress index and proportion of area of production in catchments classified according to water resource status in England & Wales. WSIr
Over Over No water Water abstracted licensed available available
East of England 0.164 34% South East 0.366 50% East Midlands 0.139 36% West Midlands 0.098 23% Yorkshire and the Humber 0.140 10% North East 0.120 0% Wales 0.088 0% South West 0.040 14% North West 0.667 1% Total 0.667 25%
23% 18% 8% 9% 26% 3% 21% 6% 21% 17%
35% 27% 44% 62% 59% 0% 66% 24% 46% 45%
8% 6% 12% 6% 5% 97% 13% 56% 33% 13%
potato production in the East of England, where a large area of production (z30% of national production) coincides with a high irrigation need and “moderate” water scarcity (WSIr ¼ 0.164). Although a significant proportion of national production is from Scotland (z15%) the low level of water scarcity (WSIr ¼ 0.017) and lower irrigation need means that it only contributes less than 1% of the total WSF (Fig. 3). 3.3. Hotspot identification When comparing the location of potato production with the resource availability status, 17% and 25% of the potato production areas (Table 4) are in WRMUs defined as over abstracted (i.e., where abstraction is causing unacceptable damage to the environment at low flows) or over licenced (i.e., where unacceptable damage could be caused if all abstractors used their full licensed amount) respectively. These account for 35% and 19% of the blue water consumption in potato production (Table 5) respectively. The East of England is clearly identified as a hotspot with the largest contribution to national BWC and 62% of the water consumed coming from WRMUs that are either over abstracted or over licenced. Potato production in the East of England is therefore potentially vulnerable to drought and the potential for increased abstraction (for expansion of production or to mitigate the impacts of climate change) are limited.
Fig. 3. Average blue water consumption, m3/t, (solid) and water scarcity footprint (hatched) for potato production in Great Britain.
T.M. Hess et al. / Journal of Cleaner Production 87 (2015) 666e674 Table 5 Blue water consumption, Mm3, for potato production and proportion of blue water consumption from catchments classified according to water resource status in England & Wales.
East of England South East East Midlands West Midlands Yorkshire and the Humber North East Wales South West North West Total
BWC Mm3
Over abstracted
Over licensed
No water available
Water available
29.5 2.5 7.8 6.5 5.0
39% 54% 35% 33% 15%
24% 15% 7% 11% 22%
33% 23% 48% 51% 61%
5% 9% 10% 5% 2%
0.3 0.4 0.8 0.5 56.4
0% 0% 7% 0% 35%
3% 35% 17% 30% 19%
0% 45% 30% 58% 40%
97% 20% 45% 13% 7%
Fig. 4 shows the area of potato production in catchments of water bodies at risk of failure to meet Good Ecological Status due to abstraction pressure for regions of GB. It shows that a larger area of Scottish production is in catchments of higher water risk than any region in England. However, because the BWC per ton in Scotland is lower (i.e., most of the water requirements of the potatoes in Scotland are met by rainfall) the volume of water consumed from high risk catchments is considerably lower than the East of England, but comparable to the Yorkshire and the Humber region in England. 4. Discussion The need for water for irrigation for potato cultivation varies across GB reflecting the range of climatic conditions under which potatoes are grown, and even in the East of England, the driest part of the country, 20% of the cropped area is reported as not irrigated. Water resource availability also varies significantly and as a result the potential impact of potato production on water scarcity, and the water related supply-chain risk, varies considerably across the country. Although the East of England accounts for about a third of the national area of potato cultivation, it accounts for more than half of the national blue water consumption for potato cultivation, whereas Scotland accounts for 15% of the area but only 6% of the total blue water consumption (Fig. 5). When weighted for water
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scarcity, the East of England is responsible for 56% of the potential national impact compared to <1% in Scotland. Although the South East of England accounts for only 3% of the area of cultivation, it has a disproportionate share of the national impact due to higher water scarcity in the region. The WSIr does not always identify the same hotspots as the CAMS water resource availability status. The potato growing areas of the South East have the highest WSIr (0.366) and the highest proportion of production in catchments that are over abstracted or over licensed. In the North East (WSIr ¼ 0.120) none of the production is from catchments that are over abstracted and only 3% from over licenced catchments in contrast to Yorkshire and the Humber, with a similar WSIr (0.140), where 36% of the production area is in over abstracted or over licenced catchments. This suggests the global-scale map of Pfister et al. (2009) may not adequately reflect the local nature of water scarcity. A number of issues have been associated with the WSI is based on the Water GAP 2 global hydrological model: 1. Scale: The Water GAP 2 model was not intended for application at small scales, and aimed to provide a global overview rather than specific details about water resource impacts (Alcamo et al., 2003b). Similarly, annual average water balances conceal significant seasonal variations. 2. Validation: The Water GAP 2 model was tested using data from 724 river gauging stations globally (Alcamo et al., 2003b) and had at least a satisfactory fit for most of Europe, however only a very limited area of south east England was included in the validation dataset. Therefore, there could be considerable uncertainty in the modelled WTA ratios for the rest of GB. 3. Withdrawal and consumption: WTA ratios may not be the appropriate indicators when assessing impact as they do not take account of environmental flows (Hoekstra and Mekonnen, 2011). 4. In industrialised countries large proportions of withdrawals are used but not consumed, returning water to the supplying water body. This may account for the apparent severe water stress in the North West, which has the same, or more extreme, values of WSI as Southern Spain and North Africa whereas the local resource assessment shows few over abstracted catchments. For this reason a consumption-to-availability ratio may be a more meaningful indicator of water scarcity (Boulay et al., 2011).
Fig. 4. Potato area (000 ha) and BWC (Mm3) for potatoes from catchments of water bodies at risk of failure to meet Good Ecological Status due to abstraction pressure in GB.
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Fig. 5. Relative area of production of potatoes, blue water consumption and contribution to water scarcity for regions of Great Britain.
5. Indices derived at the basin scale fail to differentiate between upstream and downstream water use (Jeswani and Azapagic, 2011). Water consumption may have a lower impact on water scarcity where there are fewer downstream uses. The hotspot approach suffers from its qualitative nature. There is no definition of what is a large volumetric water footprint. Such value judgements are open to interpretation which could lead to varying and inconsistent impact assessments. However, as shown in this case study, it allows the identification of places where there is potential for environmental damage resulting from water consumption which may be useful to direct further, more detailed studies. Although this study has followed commonly used methodologies used to estimate the potential contribution of agriculture to water scarcity (e.g. Chapagain and Hoekstra, 2007; Ridoutt et al., 2010; Jefferies et al., 2012) it suffers from a number of limitations: 1. The assessments only indicate the ‘potential’ contribution to water scarcity and local practice and regulation may mitigate such damage. For example, many potato growers in water stressed areas abstract during the winter and store the water in on-farm reservoirs for summer use to supplement summer
abstraction, accounting for about 20% of annual abstraction (Weatherhead, pers. com.). 2. The assessment is based on average climate data. The biggest impact on water scarcity and risk to production will not be in average years, but in dry years when both demand for irrigation water is higher and water resource availability is lower. 3. The focus on water consumption recognises that a proportion of the irrigation water withdrawn is returned to the environment, and only the proportion lost to evapotranspiration is assumed to have been lost. However, return of drainage water may not occur until the winter following abstraction. The impact on water scarcity in the short-term is therefore related to abstraction rather than consumption.
5. Conclusion This study has estimated the average annual blue water consumption for the cultivation of potatoes in GB at 61 Mm3, equivalent to 11 m3/t. However, as potatoes tend to be grown in the parts of the country where water resources are under more stress, water used for irrigating potatoes has the potential to generate a disproportionate impact on local water scarcity. If the WSI is used
T.M. Hess et al. / Journal of Cleaner Production 87 (2015) 666e674
to weight the water consumption according to water stress, this volume of water is equivalent to 115 Mm3 of water drawn equally from across the country. The East of England is a particular hotspot for potato production accounting for more than half of the potential impact on water scarcity and more than half of the potato production in this region is from catchments classified as over abstracted or over licenced. As identified by Kounina et al. (2013), there is, as yet, no preferred method for characterising the impacts of water withdrawal or consumption. Whilst the global-scale map of Pfister et al. (2009) has identified regions of potato production in GB where water withdrawal may be have a greater of lesser impact, the casestudy has shown how local information on water resource availability can provide a deeper and richer understanding of catchment specific vulnerability than may be derived from the global perspective an LCA database. Similarly, national or basin level assessments of water scarcity may be not appropriate for assessing the actual impacts of water use as there may be considerable local differences within a nation or basin. This emphasises the highly localised nature of water scarcity and the need to select an impact assessment method that is most relevant to the objectives of the study (Kounina et al., 2013). In the future, there is likely to be greater need to quantify the impact of a supply chain on the water environment in order to understand water-related risk and to support product assurance schemes or certification (Postle et al., 2011). Whilst estimates of water scarcity may identify where there is potential for water use to be having a greater impact, it fails to identify actual impact. For example, the potential impact of water withdrawal, and associated supply chain risk, may be mitigated by careful management onfarm water management (Hess et al., 2010) and especially the use of on-farm storage to allow abstraction at times of high flow (Weatherhead et al., 2010). This broad-scale assessment, however, provides a basis for targeting local data collection and support to growers to adapt to climate change and mitigate water related risks. Acknowledgements The authors would like to thank Potato Council (a division of the Agriculture & Horticulture Development Board) for the provision of statistical data on potato production in Great Britain. References €ll, P., Henrichs, T., Kaspar, F., Lehner, B., Ro €sch, T., Siebert, S., 2003a. Alcamo, J., Do Global estimates of water withdrawals and availability under current and future “business-as-usual” conditions. Hydrol. Sci. J. 48 (3), 339e348. €ll, P., Henrichs, T., Kaspar, F., Lehner, B., Ro €sch, T., Siebert, S., 2003b. Alcamo, J., Do Development and testing of the WaterGAP 2 global model of water use and availability. Hydrol. Sci. J. 48 (3), 317e337. Allan, J.A., 1998. Virtual water: a strategic resource. Global solutions to regional deficits. Groundwater 36 (4), 545e546. Berger, M., Finkbeiner, M., 2010. Water footprinting: how to address water use in life cycle assessment? Sustainability 2 (4), 919e944. ^nes, L., Margni, M., 2011. Regional Boulay, A.-M., Bulle, C., Bayart, J.-B., Desche characterization of freshwater use in LCA: modeling direct impacts on human health. Environ. Sci. Technol. 45, 8948e8957. Brown, A., Matlock, M., 2011. A Review of Water Scarcity Indices and Methodologies. Water Paper no. 106. The Sustainability Consortium, The University of Arkansas. Chapagain, A.K., Hoekstra, A.Y., 2007. The water footprint of coffee and tea consumption in the Netherlands. Ecol. Econ. 64 (1), 109e118. Chapagain, A.K., Hoekstra, A.Y., Savenije, H.H.G., Gautam, R., 2006. The water footprint of cotton consumption: an assessment of the impact of worldwide consumption of cotton products on the water resources in the cotton producing countries. Ecol. Econ. 60, 186e203. Comprehensive Assessment of Water Management in Agriculture, 2007. Water for Food, Water for Life: a Comprehensive Assessment of Water Management in Agriculture. Earthscan, and Colombo: International Water Management Institute, London.
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