The Impact of Clouds, Snow Cover and Land Use on the Climate in the Canadian Prairies R. L. Desjardins, A.K. Betts and D. Worth Ray.desjardins@agr.gc.ca Agriculture and Agri-food Canada 15th EMS Conference, Sept. 2015, Sofia, Bulgaria 1

Climate data set 15 stations in the Canadian Prairies: 1953-2011 54000 days: standard error of mean small Partition by cloud cover, sub-partition by RH Wind Specific humidity DTR Precip

15 Prairie stations: 1953-2011 These are the stations on the Prairies (and up into the boreal forest – green) where we have hourly data Hourly p, T, RH, WS, WD, opaque/reflective cloud Daily precipitation and snowdepth

Prairie Station Locations Station Name Station ID Province Latitude Longitude Elevation (m) Red Deer* 3025480 Alberta 52.18 -113.62 905 Calgary* 3031093 51.11 -114.02 1084 Lethbridge† 3033880 49.63 -112.80 929 Medicine Hat 3034480 50.02 -110.72 717 Grande Prairie* 3072920 55.18 -118.89 669 Regina* 4016560 Saskatchewan 50.43 -104.67 578 Moose Jaw 4015320 50.33 -105.55 577 Estevan* 4012400 49.22 -102.97 581 Swift Current† 4028040 50.3 -107.68 817 Prince Albert* 4056240 53.22 -105.67 428 Saskatoon* 4057120 52.17 -106.72 504 Portage-Southport 5012320 Manitoba 49.9 -98.27 270 Winnipeg*† 5023222 49.82 -97.23 239 The Pas*† 5052880 53.97 -101.1

Diurnal Climate Reduce hourly data to Diurnal cycle climate daily means: Tm , RHm, OPAQm etc data at max/min: Tx and Tn Diurnal cycle climate DTR = Tx-Tn ΔRH = RHtn – RHtx

OUTLINE The land surface and the overlying atmosphere are tightly coupled systems: eg. Canadian Prairies Seasonal & diurnal climate by station/region 220,000 days of excellent data (600 years) Large seasonal and diurnal cycles Warm season climate (JJA) Two “climates” - above and below the freezing point of water (T & Q) Snow is a fast climate switch Impact of change in cropping on climate Baseline for atmospheric model evaluation Remarkable 55-yr hourly data set with opaque/reflective cloud observations

Daily Summer Climate Partitioned by Cloud and Wind DTR increases with decreasing wind Higher Q with decreasing wind Higher θEtx with decreasing wind Betts, A.K., R. Desjardins and D. Worth (2013a), Cloud radiative forcing of the diurnal cycle climate of the Canadian Prairies. J. Geophys. Res. Atmos., 118, 1–19, doi:10.1002/jgrd.50593

Prairie Warm Season Climate 12 stations: Uniform climatology Tiny variability in DTR and ΔRH

Clouds: Warm & Cold Climates Cold-snow <0oC Transition Warm-noSnow >0oC 250,000 days (Prairies: 650 station-years: 1953-2011) Freezing point of water changes everything Stratification by percentage of clouds During the cold season air is warmest under cloudy skies and fall to a minimum at sunrise During the warm season temperatures are coolest under cloudy skies and rise to an afternoon maximum under clear skies Betts, A.K., R. Desjardins, D. Worth, S. Wang and J. Li (2014a), Coupling of winter climate transitions to snow and clouds over the Prairies. J. Geophys. Res. Atmos., 119, doi:10.1002/2013JD021168.

Specific Humidity Three specific humidity regimes Cold <0oC: Snow: stable BL, no diurnal cycle Transition near freezing: diurnal cycle with an afternoon peak Warm >0oC: unstable BL Morning and late afternoon BL coupling/uncoupling Clear is ‘drier’, while cloudy is cooler/drier/flat

N-S Albedo through Winter Prairies (SK) αs: 0.2 to 0.73 Boreal forest αs: 0.1 to 0.35 MODIS: 10day, 250m, avg. to 50x50km to latitude bands CCRS product

Snowfall and Snowmelt Temperature falls 10oC with first snowfall 50 years of data for 5 stations in Sakatchewan been averaged about the date of the first lasting snowfall in Fall, which is around 15 November. We see that in less than a week the climate cools by 10 Celsius in the Fall; and warms by a similar amount in the spring, although the melt of the winter snow pack takes longer. Snow cover acts as a fast climate switch. Temperature falls 10oC with first snowfall And rises again with snowmelt Fast transitions in ‘local climate’: a ‘climate switch’ Snow reflects sunlight Reduces evaporation and water vapor

Surface temperature fall by about 10C with fresh snowfall and increase similar amount with snowmelt- 10% decrease in days with snow cover over the Canadian Prairies means climate is 1.4C warmer So what does this mean for winter temperatures? In Alberta the snow is transient because warm chinooks often melt the snow cover. As a result, mean cold season temperature depends on the fraction of days with snow cover. The slope is even larger, 14.6 C from zero snow to 100% snow days. Less snow cover in the future will mean warmer winters. Betts et al. 2014a

Change in Cropping (SK) Ecodistrict mean for 50-km around station Saskatchewan: 25% drop in ‘SummerFallow’ Split at 1991 - has summer climate changed? Betts, A.K., R. Desjardins, D. Worth and D. Cerkowniak (2013b), Impact of land-use change on the diurnal cycle climate of the Canadian Prairies. J. Geophys. Res. Atmos., 118, 11,996–12,011, doi:10.1002/2013JD020717

Three Station Mean in SK Growing season (winter warmer) Tmax cooler; RH moister DTR and ΔRH seasonal transitions

Impact on Convective Instability Growing season Lower LCL Higher θE More Precip Betts, A.K., R. Desjardins, D. Worth and D. Cerkowniak (2013b), Impact of land-use change on the diurnal cycle climate of the Canadian Prairies. J. Geophys. Res. Atmos., 118, 11,996–12,011, doi:10.1002/2013JD020717

Summary The 60-year of hourly climate data provides a nice example of land-atmosphere interactions We have shown that the land surface and the overlying atmosphere are tightly coupled systems Impact of clouds and wind on summer climate Impact of freezing point of water (T and Q) We have demonstrated the impact of snow cover Sharp transitions with snow cover: surface albedo change from 0.2 to 0.7 Snow cover is a “climate switch”

Summary Impact of more intensive agriculture on climate. Increased transpiration changed climate Cools and moistens summer climate Lowers cloud-base and increases θE (While winter climate has warmed) With the Canadian Prairie data at 15 stations We have shown the climate of a land-atmosphere system for northern latitudes. We believe that such data sets should be extremely valuable for testing and evaluating atmospheric models