India is drying out its terrestrial carbon: An inference by multi-model
estimation of primary productivities
Michael O'Sullivan
College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom
Author ProfileStephen Sitch
College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom
Author ProfileAbstract
Terrestrial primary productivity plays a pivotal role as a forcing
factor of atmospheric CO2 and drives biospheric carbon dynamics. India
is one of the largest GHGs emitters, yet less is understood in carbon
cycling in terrestrial ecosystems. Here we explored the trend and
magnitude of gross and net productivities of India for the last two
decades (2000 – 2019) by integrating satellite observation from MODIS,
remote sensing-based CASA model and twenty DGVMs from the TRENDY
ensemble. Preliminary results exhibited a unimodal response across the
data products with an overall positive trend and a declining decadal
trend for 2010 – 2019. Alongside, the SPEI drought severity index
across various ecological zones indicated India was more positively
sensitive to wet span than the dry. We found that the ecosystems were
drastically shifting their nature to C source with a positive trend in
the productivities and were mediated by the changing climate. The
analysis also revealed the increasing decadal amplitude of GPP by 0.0884
Pg C/Year, NBP by 0.0096 Pg C/Year, NEP by 0.0195 Pg C/Year, NPP by
0.0448 Pg C/Year and NEE by 0.0161 Pg C/Year. CASA underestimated the
magnitudes but with the temporal synchronisation of the ensemble.
Seasonal variability across the agro-ecological zones was more sensitive
and was an offset for the declining productivities in the primaeval
forests of India. The monsoon season contributed to the interannual
variability of India. Higher uncertainty in productivities was observed
in the high greening areas, whereas it contradicted NBP by reflecting a
stable trend. Our results underscore the nature of C variability in the
terrestrial ecosystems of India; and, they indicate that C release has
reacted stronger than the C uptake, which was substantially inferred
from NEE across the ecological zones.