Diagnosis and attribution of recent changes in vegetation productivity and the regional water balance for the Pan-Arctic basin and Alaska
Ke
Zhang, The University of Montana, zhang@ntsg.umt.edu
John
S.
Kimball, The University of Montana, johnk@flbs.umt.edu
(Presenting)
Scott
Goetz, Woods Hole Research Center, sgoetz@whrc.org
We applied a satellite based production efficiency model (PEM) using an integrated AVHRR and MODIS FPAR/LAI time series with a regionally corrected NCEP/NCAR reanalysis surface meteorology and NASA/GEWEX solar radiation inputs to assess annual terrestrial net primary productivity (NPP) for the pan-Arctic basin and Alaska from 1983 to 2005. We also developed a satellite based evapotranspiration (ET) algorithm using GIMMS NDVI with the above meteorology inputs to estimate ET over the region. We then applied these data with in situ measurements and global precipitation records (GPCC, GPCP) to analyze changes in the regional water balance (P-ET) and the effects of natural climate oscillations (AO and PDO) on vegetation productivity and water balance patterns and anomalies.
Warming in the Boreal-Arctic region is significantly reducing the low temperature constraints on NPP by 0.43% per year (P<0.001), whereas a positive trend in vegetation moisture constraints of 0.49% per year (P=0.04) are offsetting potential benefits of a longer growing season and contributing to recent drought related disturbances in NPP. Generally positive trends in ET, precipitation and available river discharge measurements imply that the pan-Arctic terrestrial water cycle is intensifying. Increasing water deficits occurred in some boreal and temperate grasslands, consistent with regional drought records and recent satellite observations of vegetation productivity decreases. Mean annual NPP showed a positive growth trend of 0.34% per year (P=0.002) from 1983 to 2005 but with recent, large NPP declines from regional drought. The AO and PDO influence NPP by regulating the low temperature and moisture constraints to photosynthesis. Relatively strong, negative PDO phases from 1998-2002 coincided with prolonged regional drought and recent widespread water deficit and NPP declines in boreal and temperate grassland regions.
Presentation Type: Poster
Poster Session: Ecosystems Science
NASA TE Funded Awards Represented:
Kimball, John
Development of a Satellite-based Terrestrial Carbon Flux Model in Support of SMAP Carbon Cycle Science