for UK potato production - AHDB Potatoes · and irrigated potato production in England and Wales. Figure 5 Projected changes in land suitability for rainfed potato production from

Climate change and potatoesThe risks, impacts and opportunitiesfor UK potato production

Impacts on yield and water use

Climate risks to production

Photosynthesis is the driving force inproduction and governed by incoming levelsof solar radiation. However, the productionpotential is also influenced by temperatureand water availability, technology, fertiliserand crop losses. As well as the directimpacts of climate change (i.e. rainfall andtemperature), potatoes will also beparticularly sensitive to various indirecteffects, including changes in the agriculturalpotential of soils, as this effects the availabilityof water to plants and impinges on other landmanagement practices (e.g. trafficability forseed bed preparation, spraying, harvesting).

Increases in atmospheric CO2 concentrationwill also impact on crop growth by increasingthe resource efficiencies for radiation, waterand nitrogen. As a consequence, for mostcrops grown in northern Europe including

potatoes, future warmer temperatures andelevated CO2 levels are expected to result inmore favourable growing conditions,although of course there will also be somenegative consequences.

The latest climate projections (UKCP09) forthe UK suggest drier summers with highertemperatures (Figure 1) and reduced rainfall(Figure 2). But note the uncertainty aroundthese ‘mean’ projections (the dotted lines). Ingeneral, at higher latitudes a rise intemperature tends to increase thedevelopmental rate of the crop and extendsthe length of the growing season, resulting ina positive impact on crop production. On theother hand, reduced summer rainfall is likelyto increase soil moisture deficits reducingyield under rain-fed regimes and increasingthe need for supplemental irrigation.

In the future, higher summer temperatures and elevated CO2 levels shouldprovide more favourable growing conditions. But reduced summer rainfall,coupled with an increased frequency of extreme events and higher energy andfertiliser costs, will inevitably threaten rainfed and irrigated yields.

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Climate change will influence the way potato crops develop,grow and yield. It will also impact on the viability of rainfedpotato production and demand for supplemental irrigation

Figure 1 Projected changes in mean summertemperature (2020s to 2080s), for the low and highemissions for a farm site in Suffolk. Dotted lines representextreme probabilities.

Figure 2 Projected changes in mean summer rainfall(2020s to 2080s), for the low and high emissions for afarm site in Suffolk. Dotted lines represent extremeprobabilities.

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Future potato yields

To assess yield impacts, a potato crop growthmodel was used. This simulates the daily growthand development using information on climate,soil, management and cultivar. The model wasfirst calibrated using field data from three farms (inNorfolk, Suffolk and Lincolnshire) and anexperimental farm (CUF) to check that themodelled yields accurately reflected thoseobserved on-farm. Future potato yields were thensimulated for each farm for selected emissionsscenarios in the 2050s.

The projections showed only minor increases inpotato yield (+ 3 to 7%), mainly in response to theincreased radiation levels and highertemperatures. Farm production levels were foundto be limiting due to current water and fertilisermanagement practices. But when futureproduction assumed an optimal (unconstrained)irrigation and fertiliser regime then future averageyields on-farm increased by +13 to 16%.

For growers, climate change presentsan opportunity to increase potatoyield, but getting the right amount(and timing) of both water andfertiliser applications will be key. Toachieve this, growers will need betterinformation to manage climateuncertainty and match crop demandsto environmental conditions.

Future irrigation needs

Changes in climate mean supplemental irrigationis likely to become more widespread, particularlyon varieties where scab control for skin finish isimportant. For a pre-pack Maris Piper, thecombined effects of reduced rainfall (–7 to –12%)and increased crop evapotranspiration led to asignificant increase in future irrigation need (depthsapplied), ranging from +14 to 30% (Figure 3).

Clearly, these increases could have major costimplications – both on production (water andenergy), water resources and existinginfrastructure (e.g. reservoirs, pumps). Currentirrigation system capacities are typically designedfor a ‘design’ dry year (i.e. 80% probability of non-

exceedance). But Figure 3 shows that a future‘average’ year (i.e. blue 50% probability) could bemuch drier than a current ‘design’ dry year (i.e.black 80% probability).

Without adaptation, existing irrigationschemes could have insufficientcapacity to meet future irrigationneeds in approximately 50% of years,with serious consequences for potatoyield, quality and farm income.

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Figure 3 Projected future changes in annual irrigation need (mm) for pre-pack Maris Piper.

Impacts on landsuitability and soilmanagement

Land suitability classes

Four classes are frequently used by soil scientistsand growers to assess land suitability for potatoproduction - well, moderate, marginal andunsuited. Well suited has a high and sustainableproduction potential from year to year withadequate opportunity to establish the crop inaverage years at or near the optimum sowingtime. Harvesting is rarely restricted by poorground conditions. Moderately suited is wherepotential production is variable from year to yeardue to a shortage of soil water to sustain fullgrowth, or poor conditions at crop establishment.Marginally suited has a potential production thatis variable from year to year with considerablerisks, high costs, or difficulties in maintainingcontinuity of output, due to climate interactingwith soil properties, disease or pests. Forpotatoes, the criteria for unsuited land relatemainly to climate, gradient and stoniness.

Three factors are then used to distinguishbetween unsuited and suitable land; namely,potential soil moisture deficit (which reflectsagroclimate conditions), accumulatedtemperature and slope.

These identify areas where either climaticconditions (extreme cold and/or wet areas) and/orsoil characteristics (stoniness and sloping relief)would limit production. Finally, the ‘suitable’ landclass (i.e. well, moderate, or marginal) is thendetermined according to its trafficability anddroughtiness, the former measured as machinerywork days (MWD) and the latter from data on soilavailable water.

Current land suitability

By combining all these variables with nationaldatasets on soils and climate, it is possible tomap current land suitability for rainfed potatoes -and then compare this against the locations ofPCL registered growers involved in rainfedproduction (Figure 4).

Future land suitability

By imposing data on climate change, a mapshowing ‘future’ land suitability can be produced(Figure 5). This shows that in many areas, rainfedproduction will become increasingly risky.However, with supplemental irrigation, around85% of the total arable land in central and easternEngland would remain suitable for production,although most of this is in catchments wherewater resources are already over-licensed and/orover-abstracted. The expansion of irrigatedcropping is thus likely to be constrained by wateravailability. The growth in water demand due tothe switch from rainfed to irrigated cropping is

likely to be much larger than the increase in needof the currently irrigated potato crops.

In some regions rainfed production willbecome limiting – our results suggestthat by the 2050s, the area of land thatis currently well or moderately suitedfor rainfed production will decline by74% and 95% under the “most likely”climate projections for the low andhigh emissions scenario, due toincreased droughtiness.

Grower implications - variety choice

The full impacts of climate change on landsuitability are clearly more complex than the basicmaps shown here, but the results agree well withqualitative judgement. For example, based onPCL data, the cost of production would not becovered by the crop value when maincrop yieldsfall below 30 t/ha. This would set a limit for rainfedproduction in the dry regions and those havingcoarse and easily drained soils. A restricted watersupply during crucial times can also damagetuber quality to the extent that certain varietieswould be rejected by the market. This wouldforce growers to shift to varieties less susceptibleto scab or towards the processing market. Anyreduction in irrigation availability or reduction inrainfall would severely affect the profitability ofcrops such as Maris Piper and Maris Peer, whereskin finish is crucial for packing. Determinate

Changes in soils and agroclimatic conditions will influence cultivar choice,agronomic husbandry practices, and the economics of production. If rainfedproduction becomes limiting due to excessive droughtiness, then securingaccess to water for irrigation will become essential.


Climate change will affect the agricultural potential of soils bymodifying soil water balances, with consequences for potatoland suitability, trafficability and workability

crops, i.e. those that only produce a limited leafarea and have short periods of active root growthand some less-determinate varieties are verysensitive to water restrictions during mid-latecanopy expansion. Current widely grownexamples include Estima, Lady Rosetta andSaturna. Absence of rain or irrigation during theseperiods can cause premature senescence with alarge yield loss. For this reason, rainfed or limitedirrigation production with these varieties under

these climate change projections is likely to bereduced for risk of crop failure. However, the yieldresponse to irrigation of many of these varieties islarge so they will continue to be grown whereirrigation is less limited.

Production in rainfed areas is thus likely to changeto varieties that are able to either (a) survive earlydrought periods, so that they can use rainfall laterin the season (e.g. Maris Piper, King Edward,

Markies, Russet Burbank or Rooster) or (b)partition dry matter towards tuber productionduring periods of drought rather than canopyproduction which makes them more efficient inproducing yield per unit of water (e.g. Hermes orDesiree).


Current (2010) Future (2050s)

Figure 4 Current location of PCL registered rainfedand irrigated potato production in England and Wales.

Figure 5 Projected changes in land suitability for rainfedpotato production from the current baseline (2010) to thefuture (2050s). Notice how the areas of well suited landfor rainfed potatoes (green areas) shrink dramatically.

Adaptation – copingwith greater climateuncertainty

Crop management

As with all climate change impact assessments,growers need to be wary of the results andinterpret them with caution. It is neverthelessimportant to consider the range of adaptationoptions and responses available, then weigh upthe risks and plan accordingly.

The outputs from our crop modelling assumedunchanged farm practices in the future, but inreality there will of course be some degree ofautonomous adaptation even if not plannedadaptation. For potatoes, this could includeearlier planting and harvest dates, changing tobetter adapted varieties, less dependence onsoils with low water holding capacities, cropmovement to regions with more suitableagroclimate conditions and water availability, andprobably the uptake of GM technology.

Changes in soil management

Climate change is likely to lead to the dates of thelast spring frosts becoming earlier and autumnfrosts becoming rarer and/or later, therebyextending the growing season. Planting couldtherefore take place earlier as the thermalenvironment experienced by crop canopies wouldbe more favourable. However, soils would still beat field capacity, leading to the same problems inworkability that growers currently experienceduring March and April in many regions of thecountry. Reduced rainfall and higher temperatureswill result in a depletion of organic matter,increasing the risk of structural damage tosensitive soils. Harvesting windows wouldbecome longer, thereby reducing the risk ofadverse soil conditions causing harvestingproblems or crop damage.

Land management

The land suitability maps clearly show thatgrowing rainfed potatoes in England and Waleswill become increasingly risky as a result of climatechange, and limited to a few favourable areas. Incontrast, with irrigation the land suitability hardlychanges and most of the current rainfed potatoproduction could remain in its present location, if itcould be irrigated. Although only around 1% ofwater abstraction in England and Wales is usedfor irrigated agriculture, there is limited prospect ofthe industry obtaining significant additionallicensed quantities for the summer months in theface of competing demands. However, manyexisting licences are unused or underused, sowater transfers or abstraction licence tradingbetween farms may be an option, though thereare environmental arguments against re-activating“sleeper” licences in stressed catchments.

Water management

Licences are still available for high flow (off-season)abstraction in most catchments, and recent yearshave seen a significant increase in winter filled on-farm reservoirs for irrigation use in the summer.Though expensive, this gives the grower greatersecurity of supply. It seems likely that this willbecome the preferred irrigation water source forpotatoes and other high value vegetables in thesouth and east of England. But there are stillrelatively few examples of adaptation to climatechange in the UK agricultural sector, and thatmany apparent adaptive actions have actuallybeen in response to legislative or other pressures,rather than purposeful (deliberate) adaptations toperceived climate change per se, but neverthelessthey may still be useful climate changeadaptations. The current growth in on-farmreservoirs would appear to fall into this category.

Investing in water efficiency

Once irrigation water is assured but expensive, itwill become sensible to invest more heavily in waterefficiency measures; better application methods,including drip and precision irrigation, and scientificscheduling methods will become standard. Earlierplanting and harvesting would reduce water useper unit area, but with some varieties growers mightprefer to use the longer growing season to increaseyield. There has been a steady increase in averagepotato yields over the last 40 years; with nationalconsumption roughly constant this has led to agradually reducing area planted; whether this trendcan be intensified and how far it could counteractincreasing water demand is not yet clear. Othershave suggested that irrigated production mightmove north and west as an adaptation to climatechange. Given that most of the current locationsremain suited to irrigated production this may be aslow process. Many growers have sizeableinvestment in fixed assets, and may therefore preferto remain at their present locations renting landfrom neighbours with unused or partially usedlicences as a preferred way forward.


Climate change is likely to exacerbate many of the currentchallenges already facing the potato sector. The key to tacklingthese will be in adaptation – securing access to the relevantskills, resources and knowledge to increase productionefficiency, improve management and embrace new technology

Short term coping or long term planning?

Greater uncertainty in seasonal weather patternsmeans growers need to consider short-termcoping strategies as well as longer-term strategicdevelopments to reduce their vulnerability tochanging water availability. How they respond willdepend to a large extent on their perception ofrisk and the opportunities that climate changepresents to their business. Farmers generallyhave two options; either to reduce their waterneeds or try to secure additional water supplies.

Options to reduce on-farm water needs includeinvesting in improved irrigation technology(scheduling) and equipment to increaseapplication uniformity and efficiency, usingweather forecasting to increase the effective useof rainfall, encouraging deeper rooting of crops,introducing lower water use or drought tolerantcrop varieties, decreasing the overall irrigatedarea, or modifying soil structure to improve soilmoisture retention.

Options to obtain more water include purchasingland with water, obtaining additional licensedcapacity and building on-farm storage reservoirs (either individually or shared withneighbouring farms), installing rainwaterharvesting equipment, re-using waste water fromfarm buildings, or switching water supplies topublic mains where feasible.

Many of these potentialadaptations are already ‘noregret’, in that they alreadymake sense by solvingexisting water resource issues,which then contribute to afarms' future adaptability.

Dealing with uncertainty

It is important to remember that the potentialimpacts of climate change are based on longterm projections – they are not predictions ofwhat 'will' happen but rather projections of what‘might’ happen. There is a large degree ofinherent ‘uncertainty’. Figure 6 shows, forexample, the projected changes in annual rainfall

at Cambridge together with the uncertainty (errorbars). The important message here is that theuncertainty is greater than the projected futurechange – in August, for example, it is projectedthat rainfall might decline by around 20%, but itcould range from -50% to +40%. This makesadaptation planning very difficult, particularlywhere large investments are being considered(e.g. reservoirs).


Non-climate risks and building adaptivecapacity

It is important to recognise that the UK potatoindustry also faces a range of ‘non-climate’ riskswhich many would argue present a much greaterand more immediate threat than climate change.Growers have a challenging period ahead, tryingto maintain productivity whilst controllingspiraling farm costs, particularly in relation toenergy, whilst also demonstrating compliancewith regulations associated with environmentalprotection, food safety and bio-security.

In this context, coping with immediateeconomic, environmental, technological andsocietal pressures (i.e. non-climate risks) meansthat farmers are less inclined to give climatechange the priority it deserves as a key businessrisk. But climate change will exacerbate many ofthe current challenges already facing the UKpotato sector. Building adaptive capacity isneeded to provide better grower access to newskills and knowledge to increase productionefficiency. This will require new collaborationsbetween individual growers, the PCL, and otherpublic and private sectors.

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Figure 6 Projected change (%) in mean monthly rainfall at Cambridge from the current baseline to the 2050s.

Designed & produced by Visualidentity.co.uk Printed by Taylor Bloxham Leicester who have achieved the environmental

standard ISO 14001. Printed on 9 Lives 80 Silk, Totally Chlorine-free, 80% recycled, 60% post consumer waste.

This publication forms part of a project funded by the Potato Council (R505). Theproject was undertaken by Cranfield University and Cambridge University Farm(CUF).

The authors of this publication – Jerry Knox, Andre Daccache and KeithWeatherhead (Cranfield University) and Mark Stalham (CUF) wish to make it clearthat the content of this publication and the views expressed are those of theauthors and do not necessarily represent the views or policies of the organisationslisted above.

Front cover courtesy of Dr Tim Lacey (VCS Agronomy).

Acknowledgements

The authors acknowledge the Potato Council for their funding support and thefollowing growers for providing data to the project – Tim Papworth (LF Papworth Ltd ),David Matthews (GD Matthews and Son) and Peter Youngs (ESWAG).

Note: This booklet is for information purposes only. Always seek independentprofessional advice when planning developments.

This booklet should be referenced as: Knox, J.W., Daccache, A., Weatherhead,E.K., and Stalham, M (2011). Climate change and potatoes. An informationbooklet produced for PCL (AHDB), Cranfield University.

Further information:

Booklet produced by:

Jerry KnoxCranfield Water Science Institute

Cranfield University

Cranfield

Bedfordshire MK43 0AL

T: 01234 758365

E: [email protected]

W: http://www.cranfield.ac.uk/sas/

aboutus/staff/knoxj.jsp

Andre DaccacheCranfield Water Science Institute


Cranfield


T: 01234 750111 x5572



aboutus/staff/daccachea.html

Keith WeatherheadCranfield Water Science Institute


Cranfield


T: 01234 758368



aboutus/staff/weatherheadk.jsp

Mark StalhamCambridge University Farm

Agronomy Centre

219b Huntingdon Road

Cambridge CB3 0DL

T: 01223 335088


Cranfield Water Science InstituteCranfield University

Cranfield


T: 01234 758365

W: www.cranfield.ac.uk

Potato CouncilAgriculture & Horticulture Development Board

Stoneleigh Park

Kenilworth, Warks CV8 2TL

T: 02476 692051

W: www.potato.org.uk

Copies of this booklet can also bedownloaded from the Potato Councilwebsite www.potato.org.uk

for UK potato production - AHDB Potatoes · and irrigated potato production in England and Wales. Figure 5 Projected changes in land suitability for rainfed potato production from

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