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
± 0.013 Pg C Year–1, NBP by 0.0096 ± 0.001 Pg C Year–1, NEP by 0.0195
± 0.004 Pg C Year–1, NPP by 0.0448 ± 0.009 Pg C Year–1 and NEE by
0.0161 ± 0.004 Pg C Year–1. 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 for 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.