U.S. Department of the InteriorU.S. Geological Survey

Fact Sheet 2012–3123 October 2012

Famine Early Warning Systems Network—Informing Climate Change Adaptation Series

A Climate Trend Analysis of Senegal

Printed on recycled paper

19Conclusions

12°

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1990–2009 Observed

1960–1989 Observed

Major cropsurplus area

2010–2039 Predicted

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1960–1989 Observed

2010–2039 Predicted

Ziguinchor Ziguinchor

Major cropsurplus area

Figure 1. Climate change in Senegal: The left map shows the average location of the June–September 500-millimeter rainfall isohyets for 1960–1989 (light brown), 1990–2009 (dark brown), and 2010–2039 (predicted, orange). The green polygons in the foreground show the main crop surplus regions for millet and maize. The right map shows analogous changes for the June–September 30 degrees Celsius air temperature isotherms.

• Summer rains have remained steady in Senegal over the past 20 years but are 15 percent below the 1920–1969 average.

• Temperatures have increased by 0.9° Celsius since 1975, amplifying the effect of droughts.

• Cereal yields are low but have been improving.

• The amount of farmland per person is low and declin-ing rapidly.

• Current population and agriculture trends could lead to a 30 percent reduction in per capita cereal production by 2025.

shares740kilometersofcommonborder.Senegal’spopulation,estimatedat13.0millionin2011,isabout58percentrural.Theannualpopulationgrowthrateis2.5percent(CIA,2011),withanestimateddoublingtimeof27years.Agricultureemploys77percentoftheeconomicallyactivepopulaceandaccountsfor12.4percentofthegrossdomesticproduct.Agricultureismainlyrainfedanddependsheavilyupontheseasonalrain-fallamountsanddistribution.Foodstaples—millet,sorghum,maize,andrice—aregrownfordomesticconsumption,andcottonandgroundnutaregrownforexport.Cropproductionissubjecttodroughtandthreatsfrompestssuchasdesertlocusts.Senegalisanetimporterofcerealcrops.ThenorthernpartofSenegalischaracterizedbygreaterrainfallvariability,theleastdiversifiedrainfedagriculture,andextensiveherdingthatisrel-ativelymoreimportantthancropproduction.Thisregionisthemostaffectedbydrought,anditspopulationisoftenexposedtofoodinsecurity.

Thisbriefreport,drawingfromamultiyeareffortbytheU.S.AgencyforInternationalDevelopment(USAID)Fam-ineEarlyWarningSystemsNetwork(FEWSNET),examinesrecenttrendsinrainfallandairtemperatures.Theseanalysesarebasedonqualitycontrolledstationobservations.

Food Security Context

Senegal(area:196,722squarekilometers)isboundedbytheAtlanticOcean,Mauritania,Mali,Guinea,andGuinea-Bis-sau.TheGambiaisalmostentirelysurroundedbySenegaland

Figure 2. Observed and projected change in June–September rainfall and temperature for 1960–2039 (top), together with smoothed rainfall and air temperature time series for June–September for southern and north-central Senegal (bottom). Mean rainfall and temperature are based on the 1920–1969 time period.

Less than -150Less than -50

Less than -10

EXPLANATIONChange in rainfall, in millimeters

EXPLANATION

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Less than 1.25Change in temperature, in degrees Celsius

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Rainfall Remains Below Normal

RainfallinSenegaldeclinedrapidlybetween1950andthemid-1980s,andpartiallyrecoveredinthe1990s.Between2000and2009,however,therecoveryslowed,andthe2000–2009meanremainedabout15percentlowerthanthe1920–1969mean.Thepost-1980srainfallincreasesareprobablyduetothewarmingofthenorthAtlanticOcean(Hoerlingandothers,2006);asthenortherntropicalAtlantichasincreasedintemper-atureoverthisperiod,thishasdrawnthesummerrainsfurthernorth,increasingrainfallintheSahel.Theserainfallchangescanbevisualizedinthreeways:asareductionoftheareasreceivingadequaterainfallforviableagriculturallivelihoods,asmapsofanticipatedchangesinrainfall,andastimeseriesplots.

SenegalreceivesmostofitsrainbetweenJuneandSep-tember,andrainfalltotalsofmorethan500millimeters(mm)duringthisseasontypicallyprovideenoughwaterforcropsandlivestock.Between1960and1989,theregionreceiving(onaverage)thismuchrainduringJune–Septemberisshowninlightbrownintheleftpaneloffigure1andshouldbeunder-stoodtoliebeneaththedarkbrownandorangeareas.Duringthepast20years,thisregionhasretreatedsouthwardbyabout30kilometers,inalineroughlyevenwithDakar,thecapitalcity.Thisretreathaslikelyaffectedtheimportantcropgrow-ingregionsnearthecitiesofThiesandDiourbel,animportantpeanutgrowingregion(seetheObjectivesandMethodssectionforplacenamesmentionedhere).Intheeastofthecountry,the500mmcontourhasretreatedacrossaregioncategorizedbysylvo-pastoralistlivelihoods.

Rainfallreductionsandtemperatureincreasescanbevisu-alizedbycombiningtheobserved1960–2009changeswithpre-dicted2010–2039changes,basedonpersistenceoftheobservedtrends(fig.2,toppanels).Rainfalldecreasesrangefrom-150to-50mmacrossmuchofthecountry;thewesternandeasternportionsofthecountryremainsubstantiallybelowthe1960–1989average.ThewesternregionsofreducedrainfallcoincidewiththedenselypopulatedregionsofThies,Diourbel,andKaolack(seetheObjectivesandMethodssectionforpopulationtotalsandregionnames).Observedchanges(thoseoccurringbetween1960and2009)accountfor63percentofthechangemagnitudes.Asecondareaofsubstantialrainfalldeclinesliesinthesoutheastofthecountry,intheTambacoundaregion.

Smoothedtimeseries(fig.2,lowerpanel,10-yearrun-ningmeans)of1900–2009rainfall,extractedforcropgrow-ingregionsinSenegal,showthatrainfallrecoveredsincethemid-1980sbuthasnotincreasedoverthepastdecade,and2000–2009rainfallremainssubstantially(15percent)belowthe1920–1969mean.Thesetimeserieswerebasedoncropgrow-ingregionsincentralandnorthernSenegal(Thies,Diourbel,Matam,Fatick,andKaolack)andsouthernSenegal(Tamba-coundaandKolda).TheObjectivesandMethodssectionhasapopulationmapwithregionnames.

Much Warmer Air Temperatures

Since1975,temperatureshaveincreasedbyalmost0.9°Celsius(°C)acrossmuchofSenegal.Thistransitiontoanevenwarmerclimatecouldreducecropharvestsandpastureavailability,amplifyingtheimpactofdroughts.Assumingtheobservedtrendspersist,wecancreateacompositeofobservedandanticipatedairtemperaturechanges(fig.2,toprightpanel).Again,observedchangesaloneaccountfor63percentofthechangemagnitudes.Senegalisbecomingsubstantiallyhotter.Timeseriesofairtemperaturedata(fig.2,lowerpanel)showthatthemagnitudeofrecent(post-1975)warmingislargeandunprecedentedwithinthepast110years.Weestimatethatthe1975to2009warminghasbeenmorethan0.7°CforSenegalduringtheJune–Septemberrainyseason.Giventhatthestan-darddeviationofannualairtemperaturesintheseregionsislow(0.4°C),theseincreasesrepresentaverylarge(+1.2standarddeviations)changefromtheclimaticnorm.Suchwarming,inregionswithveryhighaverageairtemperatures,canamplifytheimpactofwatershortages.

Figure 3. Landscan 2008 population (ORNL, 2010) for Senegal along with Gridded Population of the World estimates (CIESIN, 2010) of 1990 to 2010 population change in millions of people.

Less than 1.5Less than 3.0

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EXPLANATIONPopulation, in millions

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Louga +0.3M

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Tambacounda +0.3M

Kolda +0.4M

Diourbel +0.4M

Saint-Louis +0.3M

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Population Growth Has Not Been Matched by Agricultural Development

In2011,theestimatedpopulationofSenegalwas13.0mil-lion(CIA,2011).Senegalhasapopulationgrowthrateof2.5percent;atthisratethepopulationwilldoubleevery27years.Between1990and2010,thepopulationofSenegalincreased64percent,withthelargestincreasesinpopulation(fig.3)occurringinDakar(+1million),Thies(+0.6million),andKaolack(+0.5million).Thispopulationexpansionwillplaceincreasingstressonlimitednaturalresources.AnalysisofcropstatisticsfromtheFoodandAgricultureOrganizationoftheUnitedNations(FAO,2011)suggeststhatincreasesincropyieldshavenotkeptpacewithpopulationgrowth.Betweenthe1960sand2000s,theamountoffarmlandperpersonhasdeclinedby300percent(from~0.3hectaresperpersonto~0.1hectaresperperson),whileyieldshaveonlyincreasedby~70percent.Acontinuationofthesetrendswillbeunfavorablefornationalfoodsecurity;projectionsfor2025basedonthesetrendssuggestthatSenegalwillproduce30percentlesscerealcropsperperson.

Some Implications For Food Security and Adaptation

Theresultspresentedheredepictacombinationofrecentrainfallvariationsandairtemperatureincreases.Whiletherain-fallincreasesfromthe1980sto1990shelpedimproveyields,theseyieldincreaseshavebeenoffsetbylargedeclinesintheamountoffarmlandperperson.Forthepast10years,however,rainfallhasremainedsteady,anditremainstobeseenifthe

earlierrainfallincreaseswillpersist.Theseasurfacetempera-turegradientoftheAtlanticOceanswingsslowlyfromnorthtosouthonatimescaleofdecades,andareversalofthecurrentstatecouldleadtoanotherprecipitousSahelianrainfalldecline,adeclineaugmentedbytheeffectsofwarmerairtemperatures.Giventhepotentialforsuchadecline,raisingyieldsinwetterareasmaybeamoreviableoptionthanextendingagricultureintomoremarginalareas.TherapidpopulationexpansioninThies,Diourbel,andKaolack,heavilypopulatedregionsthatareimportantcropproducingareas,combinedwithfurtherdryingandwarming,couldleadtoincreasedfoodinsecurityintheseregions.

Objectives and Methods

TheFEWSNETInformingClimateChangeAdaptationseriesseekstoguideadaptationeffortsbyprovidingsubnationaldetailonthepatternsofclimatetrendsalreadyobservedinanappropriatelydocumentedrecord.Whethertheseobservedtrendsarerelatedtonaturalclimatevariations,globalwarming,orsomecombinationofthetwoislessimportantthanknowingnowwheretofocusadaptationefforts.

TheseFEWSNETreportsrelyonrigorousanalysisofstationdata,combinedwithattributionstudiesusingobservedclimatedata.ThisbriefreportexaminesSenegalrainfallandtemperaturetrendsforthelast110years(1900–2009)usingobservationsfrom98rainfallgaugesand13airtemperaturestationsfortheprimaryrainyperiod,June–September.Thedatawerequalitycontrolled,andthemean1960–1989andmean1990–2009stationvaluescalculated.Thedifferencebetweenthesemeanswasconvertedinto1960–2009trendobserva-tionsandinterpolatedusingarigorousgeo-statisticaltechnique(kriging).Krigingproducesstandarderrorestimates,whichcanbeusedtoassesstherelativespatialaccuracyoftheidentifiedtrends.Dividingthetrendsbytheassociatederrorsallowsustoidentifytherelativecertaintyofourestimates(Funkandothers,2005;Verdinandothers,2005;BrownandFunk,2008;FunkandVerdin,2009;Funkandothers,2012).Readersinterestedinmoreinformationcanfindthesepublicationsathttp://early-warning.usgs.gov/fews/reports.php.

ThisreportwaswrittenbyChrisFunk(USGS),JimRow-land(USGS),AlkhalilAdoum(UCSB),GaryEilerts(USAID),JamesVerdin(USGS),andLibbyWhite(UCSB).Itbuildsuponamultiyearresearchproject(seereferences)carriedoutunderaUSAID-fundedFEWSNETagreementwithUSGS.

References

Brown,M.E.,andFunk,C.C.,2008,Foodsecurityunderclimatechange:Science,v.319,p.580–581.(Alsoavailableonlineatftp://chg.geog.ucsb.edu/pub/pubs/Science_2008.pdf.)

CIA(CentralIntelligenceAgency),2011,TheWorldFactbook,accessedDecember15,2011,athttps://www.cia.gov/library/publications/the-world-factbook/geos/sg.html.

CIESIN(CenterforInternationalEarthScienceInformationNetwork),2010,Griddedpopulationoftheworld,version3,accessedMay5,2010,athttp://sedac.ciesin.columbia.edu/gpw/.

FAO(FoodandAgricultureOrganizationoftheUnitedNations),2011,FAOSTAT:AccessedDecember15,2011,athttp://faostat.fao.org.

Funk,C.,Senay,G.,Asfaw,A.,Verdin,J.,Rowland,J.,Kore-cha,D.,Eilerts,G.,Michaelsen,J.,Amer,S.,andChoular-ton,R.,2005,RecentdroughttendenciesinEthiopiaandequatorial-subtropicaleasternAfrica:Washington,DC,U.S.AgencyforInternationalDevelopment.(Alsoavailableathttp://earlywarning.usgs.gov/fews/pubs/FEWSNET_2005.pdf.)

Publishing support provided by the Rolla Publishing Service Center

FunkC.,andVerdin,J.P.,2009,Real-timedecisionsupportsystems–TheFamineEarlyWarningSystemNetwork,inGebremichael,M.,andHossain,F.,eds.,Satelliterainfallapplicationsforsurfacehydrology:Netherlands,Springer,p.295–320.(Alsoavailableonlineathttp://earlywarning.usgs.gov/fews/pubs/SatelliteRainfallApplications_2010.pdf.)

Funk,C.,Michaelsen,J.,andMarshall,M.,2012,Mappingrecentdecadalclimatevariationsinprecipitationandtemper-atureacrossEasternAfricaandtheSahel,chap.14inWard-low,B.,Anderson,M.,andVerdin,J.,eds.,Remotesensingofdrought—Innovativemonitoringapproaches:TaylorandFrancis,25p.(Alsoavailableathttp://earlywarning.usgs.gov/fews/pubs/mapping_decadal_variations.pdf.)

Hoerling,M.,Hurrell,J.,Eischeid,J.,andPhillips,A.,2006,Detectionandattributionoftwentieth-centurynorthernandsouthernAfricanrainfallchange:JournalofClimatology,v.19,p.3,989–4,008.

ORNL(OakRidgeNationalLaboratory),2010,Landscan2008population,accessedMay5,2010,athttp://www.ornl.gov/sci/landscan/.

Verdin,J.P.,Funk,C.C.,Senay,G.B.,andChoularton,R.,2005,Climatescienceandfamineearlywarning:PhilosophicalTransactionsoftheRoyalSocietyB–BiologicalSciences,v.360,no.1463,p.2,155–2,168.(Alsoavailableathttp://earlywarning.usgs.gov/fews/pubs/RoyalSociety.pdf.)