Attribution of divergent northern vegetation growth responses to lengthening non-frozen seasons using satellite optical-NIR and microwave remote sensing

Youngwook Kim, J. S. Kimball, K. Zhang, K. Didan, I. Velicogna, K. C. McDonald

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

The non-frozen (NF) season duration strongly influences the northern carbon cycle where frozen (FR) temperatures are a major constraint to biological processes. The landscape freeze-thaw (FT) signal from satellite microwave remote sensing provides a surrogate measure of FR temperature constraints to ecosystem productivity, trace gas exchange, and surface water mobility. We analysed a new global satellite data record of daily landscape FT dynamics derived from temporal classification of overlapping SMMR and SSM/I 37 GHz frequency brightness temperatures (Tb). The FT record was used to quantify regional patterns, annual variability, and trends in the NF season over northern (≥45°N) vegetated land areas. The ecological significance of these changes was evaluated against satellite normalized difference vegetation index (NDVI) anomalies, estimated moisture and temperature constraints to productivity determined from meteorological reanalysis, and atmospheric CO2 records. The FT record shows a lengthening (2.4 days decade-1; p < 0.005) mean annual NF season trend (1979-2010) for the high northern latitudes that is 26% larger than the Northern Hemisphere trend. The NDVI summer growth response to these changes is spatially complex and coincides with local dominance of cold temperature or moisture constraints to productivity. Longer NF seasons are predominantly enhancing productivity in cold temperature-constrained areas, whereas these effects are reduced or reversed in more moisture-constrained areas. Longer NF seasons also increase the atmospheric CO2 seasonal amplitude by enhancing both regional carbon uptake and emissions. We find that cold temperature constraints to northern growing seasons are relaxing, whereas potential benefits for productivity and carbon sink activity are becoming more dependent on the terrestrial water balance and supply of plant-available moisture needed to meet additional water use demands under a warming climate.

Original languageEnglish
Pages (from-to)3700-3721
Number of pages22
JournalInternational Journal of Remote Sensing
Volume35
Issue number10
DOIs
StatePublished - May 2014

Funding

This work was conducted at the University of Montana under contract to the National Aeronautics and Space Administration, with funding support provided by the NASA Terrestrial Ecology and Hydrology programmes. The FT-ESDR and VIP NDVI data records used for this investigation were provided by the National Snow and Ice Data Center (NSIDC) and the University of Arizona, with funding support provided by the NASA measures (Making Earth System Data Records for Use in Research Environments) programme. The GLOBALVIEW-CO2 data record used for this study was provided by the NOAA ESRL (Earth System Research Laboratory).

FundersFunder number
National Aeronautics and Space Administration

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