Satellite detection of Northern Hemisphere Non-Frozen season changes and associated impacts to vegetation growing seasons
Abstract
The landscape freeze-thaw (FT) signal from satellite microwave remote sensing is closely linked to vegetation phenology, productivity and land-atmosphere trace gas exchange where seasonal frozen temperatures are a major constraint to plant growth. We applied a temporal change classification of 37 GHz, vertically polarized brightness temperature (Tb) measurements from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) to classify daily FT status over global land areas where seasonal frozen temperatures influence ecosystem processes. A temporally consistent, long-term (>30 year) FT record was created ensuring cross-sensor consistency through pixel-wise adjustment of the SMMR Tb record based on empirical analyses of overlapping SMMR and SSM/I measurements. The resulting FT record showed mean annual spatial classification accuracies of 91 (+/-8.6) and 84 (+/-9.3) percent for PM and AM overpass retrievals relative to air temperature measurements from global weather stations. The FT results were also compared against other measures of biosphere activity including satellite derived vegetation greenness (NDVI) and terrestrial net primary productivity (NPP), tower CO2 flux measurements and seasonal patterns of atmospheric CO2 concentrations from northern (>50°N) monitoring sites. A strong (P<0.001) increasing (0.189 days yr-1) trend in Northern Hemisphere mean annual non-frozen period is largely driven by an earlier (-0.149 days yr-1) spring thaw trend and coincides with a 0.033 °C yr-1 regional warming trend. The FT defined non-frozen period largely bounds the vegetation growing season determined from NDVI greening and net ecosystem CO2 uptake for tower sites representing major ecoregion types. Earlier spring thawing and a longer non-frozen season generally enhance atmosphere carbon sequestration and benefit vegetation growth inferred from NDVI and NPP anomalies, with greater benefits at higher (>45°N) latitudes and upper elevations. The FT record also shows a positive (0.199 days yr-1) trend in the number of transitional (AM frozen and PM non-frozen) frost days, resulting in reduced photosynthetic activity inferred from tower and NDVI measurements. The relative benefits of earlier and longer non-frozen seasons for vegetation growth and productivity under global warming may be declining due to opposing increases in disturbance, drought and frost damage related impacts. Portions of this work were conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration. Key Words: Freeze thaw, SMMR, SSM/I, climate change, global warming, MODIS, NDVI, NPP, carbon sequestration, vegetation growing season, phenology, ESDR, CDR, NASA MEaSUREs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B51M0602K
- Keywords:
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- 0426 BIOGEOSCIENCES / Biosphere/atmosphere interactions;
- 0704 CRYOSPHERE / Seasonally frozen ground;
- 1630 GLOBAL CHANGE / Impacts of global change;
- 1823 HYDROLOGY / Frozen ground