DecliningSnowCoverReducesRadia4veCoolingfromHistoricLandUseChangeintheWesternGreatLakesRegionBethanyBlakely,AdrianRocha,JasonMcLachlan

DepartmentofBiologicalSciences,UniversityofNotreDame,NotreDameIN

°

LandSurfaceChanges CombinedForcing

Acknowledgements

LiteratureCited

Ques4ons

Reconstruc4ngHistoricVegeta4on

v ForestcoverhasdecreasedsinceEuropeanseMlementv Deciduous and mixed forests have mostly replacedevergreenforestswhereforestregrowthisoccurring

Figure2:Vegeta4oncoveronthe(a)historiclandscape(b)modernlandscape.Percentchangeinvegeta4oncoverisshownin(c).WeusedgriddedPublicLandSurvey(PLS)data to assign land cover classifica4ons using Interna4onal Geosphere BiosphereProgramme (IGBP) designa4ons as follows: evergreen forest ( > 60% evergreen sp.cover), deciduous forest (> 60% deciduous sp. cover), mixed forest ( > 60% forestcover,mixedcomposi4on),vegeta4onmosaic(20%-60%forestcover),andcropland/grassland(<20%forestcover).

TheMidwestintheAnthropocene

v Land use and snowcoverhavechangedin the Great LakesR e g i o n s i n c eE u r o p e a nseMlement

v These changes alterthe brightness andtemperature of theland surface withimp l i ca4ons forclimate

Figure 1: Typical land use history in theGreatLakesRegion. Landscapes (a)beforedeforesta4on, (b) immediately a_erdeforesta4on,and(c,d)today.

IwouldliketothankA.RochaandJ.McLachlanfortheirideasandguidanceonthisproject,X.YangandB.NaimifortheirMODISprocessingscripts,theMcLachlanlabundergraduatesfordigi4zingPLSdata,andS.Goringforcrea4onofthegriddedPLSproduct.ThisprojectisfundedbytheArthurJSchmiMFounda4on,thePaleonproject,andtheUniversityofNotreDame.

v How have historic changes in land usea l t e red t he a lbedo and su r f a cetemperatureoftheGreatLakesRegion?

v What are the radia2ve forcings of thesechanges and how do they offset eachother?

v Howhastheclima4callydrivendecreaseinsnowcoverimpactedtheseeffects?

Reconstruc4ngLandSurfaceTraits

SnowCoverChanges

MODISAlbedo

MODISSnow

MODISLandCover

MODISQualityControlandTen-yearAggrega4on

ReconstructedVegeta4on

MODISSurfaceTemp.

MODISLandCover

ReconstructedAlbedo ReconstructedSurfaceTemp.

Figure3:Methodologyforreconstruc4nghistoricalbedoandsurfacetemperature,calcula4ngchangessinceEuropeanseMlementandcalcula4ngradia4veforcingofthosechanges.Interpola4onsofmodernMODISdatawereusedtoassignbiophysicalproper4estothemapofhistoricallyreconstructedvegeta4on.

Albedo SurfaceTemperatureProcess

Model

Assign

AlbedoDifferencesandRadia4veForcing

SurfaceTemp.DifferencesandRadia4veForcing

Compare

•  Chen,J.,Jönsson,P.,Tamura,M.,Gu,Z.,Matsushita,B.,&Eklundh,L.(2004).Asimplemethodforreconstruc4ngahigh-qualityNDVI4me-seriesdatasetbasedontheSavitzky–Golayfilter.RemoteSensingofEnvironment,91(3–4),332-344.

•  Zhao,K.,&Jackson,R.B.(2014).Biophysicalforcingsofland-usechangesfrompoten4alforestryac4vi4esinnorthamerica.EcologicalMonographs,84(2),329-353.

a b

c d

a b

c

The nega2ve forcings of historic land use changecurrently provide a “discount” on regionalwarmingbut thesebenefits are likely todisappearwith2meas snow cover decreases and forest regrowthcon2nues

LowessInterpola4onsofMODISdata

GHCNSWE2000-2010

GHCNSWE1900-1910

ReconstructedAlbedo

Calculatedshi_insnowseasonality:

Hsnownorm-Msnownorm

Appliedto

Seasonallyshi_edAlbedo

Seasonalshi_differencesandradia4veforcing

v Surfacetemperatureforcingisstronglyposi4ve in summer and weaklynega4veinwinter.

v Net forcing from surface temperaturechangeweightedbydaylengthissmallandposi4ve(μ=+0.37W/m2)

-2°C

+2°C

Figure 6: Surface temperature differences for Winter (Jan 1),Spring (Apr 7), Summer (Jul 12), and Fall (Oct 16). Nega4vevalues (green) indicate areas where modern surfacetemperatureislowerthanhistoricsurfacetemperature.

Figure7:Seasonalprofileof radia4ve forcing for surface temperaturechange.Grayshadingdesignates10%and90%quan4les.

v Springsnowmeltisdelayed,increasingalbedoinFeb-May

v Spring forcings aretypically an ordero f m a g n i t u d elargerthanfall

v Net forcing fromthe shi_ in snows e a s o n a l i t y i sposi4ve but small(+0.45W/m2)

Figure5:Albedodifferences forWinter (Jan1), Spring (Apr7),Summer(Jul12),andFall(Oct16).Posi4vevalues(green)indicateareaswheremodernalbedo ishigher thanhistoricalbedo.

-0.3

+0.3

SurfaceTemperature

Albedo

Figure4: Seasonalprofileof radia4ve forcing foralbedochange.Grayshadingdesignates10%and90%quan4les.

Figure 8: Spring (a) and Fall (b) shi_s in Albedo due to changes in snowcover. Black lines represent historically reconstructed Albedo shi_ed toreflect historic snow cover. Red lines show non-shi_ed historicallyreconstructedAlbedo.

Figure9:Seasonalprofileofradia4veforcingforsurfacetemperaturechange.Grayshadingdesignates10%and90%quan4les.

Figure 10: Methodology for seasonalshi_inalbedobasedonchangesinsnowcover. Global Historic Climate Network(GHCN) snow water equivalents wereusedtocalculateseasonalshi_

v Surfacetemperaturechangesoffset23%ofyear-roundalbedoforcing

v Clima4cshi_sinsnowseasonalityoffset18%ofyear-roundalbedoforcing

v Combinedforcingis41%lowerthanvegeta4on-mediatedalbedoforcingalone

Figure11:Albedo(a)andtotal(b)radia4veforcingsofland use change in the Great Lakes Region. Dashedlinesindicatecomponentforcings.

Conclusions

v Albedo forcing is always nega4vewiththegreatestcoolinginwinter

v Overall radia4ve forcing fromalbedo change is large andnega4ve(μ=-1.64W/m2)

a b

a

b