Climate challenges facing northern grasslands and ranches

Transcription

1 Climate challenges facing northern grasslands and ranches Paul C. Stoy 1, Tobias Gerken 1, Gabriel Bromley 1, Ben Poulter 2 Paul.stoy@montana.edu 1 Montana State University 2 NASA Goddard waferx.montana.edu bit.ly/stoygscholar

2 Acknowledgements Funding NSF (DEB , OIA ) Montana Wheat and Barley CommiWee The Graduate School at Montana State University USDA NIFA Hatch Data NaYonal Weather Service/NOAA CRU ECMWF IPCC U.S. Drought Monitor Kelsey Molloy & Tanja Franssen for the invitayon

3 Outline 1. Future climate trends 2. Recent (decadal) climate changes 3. The 2017 Flash Drought

4 Will the Northern Plains get warmer? Yes, and perhaps we-er, too Stoy et al. (2018) Bioscience Figure credit: Ben Poulter

5 1) Have the Northern Plains warmed in recent decades? Yes and no.

6 2) Why is there a cooling trend during summer?

7 3) Is there a large country to our north? MJJ mean temperature trend, 1970s- 2016*, ECMWF- ERA- 20 reanalysis. Figure credit: Gabriel Bromley

8 The cooling trend is most pronounced in Spring / early summer: April- May- June Canadian Prairie Ecozone NEON Northern Great Plains Figure credit: Gabriel Bromley

9 It is somewhat unique globally Northern Great Plains World Number of pixels Air temperature trend ( C / decade) Figure credit: Gabriel Bromley

10 The North American Great Plains are also now more humid MJJ mean RH trend, 1970s- present, ECMWF- ERA- 20 reanalysis. Figure credit: Gabriel Bromley

11 Glasgow receives 3x more rain in May now than it did in the 1990s Figure credit: Tobias Gerken

12 Why? Probably land use changes In the Canadian Prairies over the past 4 decades: Summer maximum temperature: - 1 C trend Precip: + 10 mm/decade trend - 6 W m - 2 summer forcing! Anthropogenic warming +2.5 W m - 2 Gameda et al., (2007) BeWs et al. (2013 a,b) Raddatz (2007)

13 There is now ca. 23 Mha less summer fallow than before Summer fallow (Mha) Canada United States Total Year

14 The largest fallow changes are in Saskatchewan Summer fallow (Mha) 16 Canada Saskatchewan Alberta 14 Manitoba Other Year

15 and North Dakota. Summer fallow (Mha) (2) (3) (1) Colorado Kansas Montana Nebraska N. Dakota Oklahoma S. Dakota Texas Other Year Is this a win- win- win scenario for regional climate, soil conserva6on, and income?

16 Cropping systems impact the water and energy fluxes that impact regional climate EvapotranspiraYon Sensible Heat Cumulative ET (mm) Winter Wheat Spring Wheat Fallow Winter Wheat Harvest Spring Wheat Harvest Cumulative H (MJ m -2 ) Winter Wheat Spring Wheat Fallow Winter Wheat Harvest Spring Wheat Harvest 50 0 April May June July Aug Sept A April May June July Aug Sept A Vick, Stoy, Tang & Gerken (2016): Measurements from the Judith Basin, MT

17 Atmospheric boundary layer (ABL) lived condensawon level (LCL) crossing is a necessary but not sufficient condiwon for convecwve precipitawon Manoli et al. (2016) (related to evapotranspirayon) See also: Findell and Eltahir (2003a,b), Juang et al. (2007a,b), Koenings et al. (2010), Porporato (2009) and many more

18 Decadal changes in surface and atmospheric condiwons at Glasgow (GGW) Gerken, Bromley & Stoy (2018) Journal of Hydrometeorology Figure credit: Tobias Gerken

19 ConvecWve likelihood is now 10% greater in NE Montana ConvecWon is sensiwve to the land surface in the early season Probability of crossing a) Bo Figure credit: T. Gerken Gerken, Bromley & Stoy (2018) Journal of Hydrometeorology

20 Alternate hypotheses Cold air incursion? Canadian Prairie Ecozone NEON Northern Great Plains Other aspects of the general circulabon No Bll agriculture (brighter surface) Other land use changes Figure credit: Gabriel Bromley Moisture advecbon (irrigabon)?

21 Example: CRP rise and fall Grassland management (data for the Upper Missouri)

22 A problem: This was the summer outlook issued last May 18

23 PrecipitaWon during the last 30 years (blue) versus last year (black) Figure credit: Tobias Gerken

24 Was the atmosphere giving us clues that drought was imminent? ConvecYve rain Unlikely é ê Likely ConvecYve triggering potenyal Near- surface dryness Last May was drier than an average August!! 30-year climatology 2017 Figure credit: Tobias Gerken

25 The running mean of days for which convecwve precip. was unlikely year mean +/- s.d. Early March was already anomalously dry in Glasgow

26 Summary. In the Northern North American Great Plains: 1) Warming except during spring / early summer; 2) ConvecYve precipitayon is coupled to land surface funcyon early in the growing season (and land management trends make precipitayon more likely); 3) The 2017 Flash drought was preceded by a breakdown of land- atmosphere feedbacks; 4) The response of land management to climate and vice versa should be further explored. Natural-Human coupling Human system Natural system Human-Natural coupling