1. 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
Agriculture and Agri-food Canada
15th EMS Conference, Sept. 2015, Sofia, Bulgaria 1

2. 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

3. 15 Prairie stations:
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

4. Prairie Station Locations
Station Name
Station ID
Province
Latitude
Longitude
Elevation (m)
Red Deer*
Alberta
52.18
905
Calgary*
51.11
1084
Lethbridge†
49.63
929
Medicine Hat
50.02
717
Grande Prairie*
55.18
669
Regina*
Saskatchewan
50.43
578
Moose Jaw
50.33
577
Estevan*
49.22
581
Swift Current†
50.3
817
Prince Albert*
53.22
428
Saskatoon*
52.17
504
Portage-Southport
Manitoba
49.9
-98.27
270
Winnipeg*†
49.82
-97.23
239
The Pas*†
53.97
-101.1

5. 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

6. 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

7. 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: /jgrd.50593

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

9. Clouds: Warm & Cold Climates
Cold-snow <0oC Transition Warm-noSnow >0oC
250,000 days (Prairies: 650 station-years: )
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: /2013JD

10. 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

11. 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

12. 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

13. 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

14. Change in Cropping (SK)
Ecodistrict mean for 50-km around station
Saskatchewan:
25% drop in ‘SummerFallow’
Split at 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: /2013JD020717

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

16. 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: /2013JD020717

17. 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”

18. 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