Frozen season impacts on northern high latitude vegetation growth under cold temperature and moisture constraints

Youngwook Kim, University of Montana-NTSG/FLBS, youngwook.kim@ntsg.umt.edu (Presenter)
John S Kimball, University of Montana, johnk@ntsg.umt.edu
Ke Zhang, University of Montana, ke.zhang@umontana.edu
Kamel Didan, The University of Arizona, didan@email.arizona.edu
Kyle McDonald, The City College of New York, kmcdonald2@ccny.cuny.edu

The duration of the frozen season strongly influences vegetation dormancy and productivity at higher latitudes and upper elevations where frozen temperatures are a major constraint to plant growth. The landscape freeze-thaw (FT) signal from satellite microwave remote sensing is closely linked to frozen temperature constraints to vegetation phenology, productivity, land-atmosphere trace gas exchange and surface water mobility. We developed a consistent global record of daily landscape FT dynamics at moderate (~25-km) spatial resolution using a temporal change classification of overlapping 37 GHz frequency brightness temperatures (Tb) from AM and PM overpass retrievals of the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) sensor records. A temporally consistent and continuous long-term (from 1979) FT record was created that distinguishes daily frozen, non-frozen and transitional (AM frozen and PM non-frozen) conditions. The FT record is used to quantify variability and regional trends in frozen seasons and transitional frost days over the northern high latitude (NHL) domain. The ecological significance of these changes is evaluated against atmospheric CO2 seasonal cycles, satellite NDVI summer growth anomalies and estimated moisture and temperature constraints to productivity determined from global meteorological reanalysis. The FT metrics show a significant mean regional trend toward shorter (-2.4 days per decade; p<0.001) frozen seasons over the 30+ year record, driven largely by earlier spring thawing (-2.1 days per decade; p<0.001). A declining frozen season coincides with regional warming and is predominantly enhancing vegetation growth in cold temperature constrained regions, while these effects are reversed or reduced in more moisture constrained areas. Shorter frozen seasons increase the atmospheric CO2 seasonal amplitude by enhancing ecosystem productivity and CO2 emissions.

Presentation: 2013_Poster_Kim_54_28.pdf (520k)

Presentation Type:  Poster

Session:  Poster Session 2-B   (Wed 4:30 PM)

Associated Project(s): 

• Related Activity or Previously Funded TE Activity

Poster Location ID: 54